Engine Control System - Tests W/codes - DTC p0135-p0204 — Cadillac Escalade GMT400 (1998-2000)

MODEL IDENTIFICATION

Vehicle model is identified by fourth character (cars), or fifth character (trucks) of Vehicle Identification Number (VIN). VIN is stamped on metal pad on top of left end of instrument panel, near windshield. See MODEL IDENTIFICATION (CARS) table, or MODEL IDENTIFICATION (TRUCKS) table under MODEL IDENTIFICATION in INTRODUCTION article.

DTC P0135: HO2S HEATER CIRCUIT-BANK 1, SENSOR 1 (3.0L "V" BODY)

Note. For circuit reference, see appropriate wiring diagram in WIRING DIAGRAMS article.

Circuit Description

Using Heated Oxygen Sensors (HO2S) for fuel control decreases amount of time required to enter closed loop operation. Heated oxygen sensors, when used post-catalyst, ensure sufficient heat is maintained for accurate catalyst monitoring.

When ignition is turned on, switched battery voltage is supplied to HO2S heaters via main relay. ECM controls heater operation by first modulating ground circuit when sensors are cold, and then turning them on continuously after predetermined amount of time. This prevents possibility of thermal shock to sensors by controlling sensor's rate of heating. As heater reaches operating temperature, HO2S voltage responds by changing from bias voltage range to normal operation.

On cold start, ECM will track how much time it takes for HO2S voltage to go above or below bias voltage range. If ECM determines that it took too much time for HO2S to enter into normal operating range, this DTC will set. The time it takes HO2S to reach operating temperature is based on amount of airflow into engine and start-up coolant temperature.

For duplication of DTC, ensure battery voltage is 11-15.5 volts, heater output stage is active, and engine is running.

Diagnostic Procedures

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-introduction__on-board-diagnostic-obd-system-check) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Check for exhaust leaks between HO2S 1 and HO2S 2. If a leak is found, go to step 7 . If no leaks are found, go to next step.
Turn ignition off. Disconnect HO2S 1. Check for faulty harness connections. If connections are faulty, go to step 8 . If connections are okay, go to next step.
Turn ignition off. Measure sensor resistance between sensor housing and HO2S 1 heater control circuit. If resistance is less than 100 ohms, go to step 9 . If resistance is not less than 100 ohms, go to next step.
Disconnect ECM harness connector. Using a test light connected to battery positive, probe HO2S 1 heater control circuit at ECM harness connector. If test light illuminates, go to step 10 . If test light does not illuminate, go to next step.
Check for continuity in HO2S 1 heater control circuit between HO2S 1 and ECM. If continuity is present, see «DIAGNOSTIC AIDS»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p0135-p0204__diagnostic-aids) . If continuity is not present, go to step 11 .
Repair exhaust leaks as necessary. After repairs, go to step 12 .
Repair terminals as necessary. After repairs, go to step 12 .
Replace HO2S 1. After repairs, go to step 12 .
Repair short to ground. After repairs, go to step 12 .
Repair open circuit. After repairs, go to next step.
Using scan tool, clear DTCs. Start engine and operate vehicle under conditions required to set this DTC. If scan tool indicates this test ran and passed, go to next step. If scan tool does not indicate this test ran and passed, go to step 2 .
Using scan tool, select CAPTURE INFO, REVIEW INFO function. If any undiagnosed DTCs are displayed, go to applicable DTC test. If no undiagnosed DTCs are displayed, system is okay.

Diagnostic Aids

For any test that requires probing ECM or component harness connectors, use Connector Test Adapter Kit (J-35616-A). This will prevent damage to harness connector terminals. Check for the following conditions

HO2S pigtail or harness may be mispositioned and contacting exhaust system. Inspect harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, poor terminal-to-wire connection, corrosion or water intrusion.

An oxygen supply inside HO2S is necessary for proper operation. This supply of oxygen is provided through HO2S wiring harness. All HO2S wires and connections should be inspected for breaks or contamination. Repair as necessary.

DTC P0135: HO2S HEATER CIRCUIT-SENSOR 1 (3.1L "N" & "W" BODIES & 3.4L "N" BODY & "U" SERIES)

Note. For circuit reference, see appropriate wiring diagram in WIRING DIAGRAMS article.

Powertrain Control Module (PCM) runs heater test only after a cold start and only once during an ignition cycle. When engine is started, PCM monitors HO2S 1 voltage. When HO2S 1 voltage indicates a sufficiently active sensor, PCM looks at how much time has elapsed since start-up. If PCM determines that too much time was required for HO2S 1 to become active, DTC P0135 will set.

For duplication of DTC, ensure

No active misfire, fuel injector circuit, TP sensor, EVAP system, IAT sensor, MAP sensor, fuel trim, EGR, ECT sensor, MAF sensor or CKP sensor DTCs are set.
ECT and IAT is less than 95°F (35°C) at start-up.
ECT and IAT are within 42°F (6°C) of each other at start-up.
Average MAF for the sample period is less than 20 gm/s.
Battery voltage is greater than 8 volts and less than 18 volts.
HO2S 1 signal voltage remains within 150 mV of bias voltage (about 450 mV) for a greater amount of time than it should.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-introduction__on-board-diagnostic-obd-system-check) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Allow engine to completely cool down before proceeding. Turn ignition on, with engine off. Using scan tool, monitor HO2S 1 voltage. If voltage changes from about 450 mV to greater than 600 mV or from about 450 mV to less than 300 mV, see «DIAGNOSTIC AIDS»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p0135-p0204) . If voltage does not change as indicated, go to next step.
Remove and inspect fuse for HO2S 1 ignition feed circuit. If fuse is blown, go to step 15 . If fuse is okay, go to next step.
Turn ignition off. Disconnect HO2S 1 connector. With test light connected to ground, probe ignition feed circuit terminal at HO2S 1 harness connector. If test light illuminates, go to next step. If test light does not illuminate, go to step 7 .
Connect a test light between heater ground circuit and ignition feed circuit terminals at HO2S 1 harness connector. If test light illuminates, go to next step. If test light does not illuminate, go to step 8 .
Allow HO2S 1 to cool for a minimum of 10 minutes. Using DVOM, measure resistance between ignition feed circuit and heater ground circuit terminals at HO2S 1 pigtail. If resistance is 3-10 ohms, go to step 9 . If resistance is not 3-10 ohms, go to step 14 .
Repair open in HO2S 1 ignition feed circuit. After repairs, go to step 16 .
Repair open in HO2S 1 heater ground circuit. After repairs, go to step 16 .
Check for poor connection at HO2S 1 harness terminals. Repair as necessary. After repairs, go to step 16 . If terminals are okay, go to next step.
Turn ignition off. Disconnect PCM harness connectors. Measure resistance of signal circuit and ground circuit between PCM and HO2S 1 harness connector. If both readings are less than 5 ohms, go to next step. If one or both readings are 5 ohms or greater, repair open in appropriate circuit. After repairs, go to step 16 .
Check for poor signal circuit or ground circuit terminal connection at HO2S 1 harness connector. Repair as necessary. After repairs, go to step 16 . If terminals are okay, go to next step.
Check for poor HO2S 1 ground circuit terminal at PCM. Repair as necessary. After repairs, go to step 16 . If terminal is okay, go to next step.
Check for poor HO2S 1 signal circuit terminal at PCM. Repair as necessary. After repairs, go to step 16 . If terminal is okay, go to next step.
Replace HO2S 1. After repairs, go to step 16 .
Locate and repair short to ground in HO2S 1 ignition feed circuit. Replace fuse. After repairs, go to next step.
Allow engine to completely cool down before proceeding. Using scan tool, clear DTCs. Turn ignition on, with engine off. Using scan tool, monitor HO2S 1 voltage. If voltage changes from about 450 mV to greater than 600 mV or from about 450 mV to less than 300 mV, system is okay. If voltage does not change as indicated, go to step 2 .

Check for poor connection at PCM. Check for damaged wiring harness. An intermittent problem can be caused by a poor connection, rubbed-through wire insulation or broken wire inside insulation. Reviewing FAILURE RECORDS vehicle mileage since diagnostic test last failed may help determine how often condition that caused DTC to be set occurs.

DTC P0135: HO2S HEATER CIRCUIT-SENSOR 1 (3.5L "W" BODY)

Note. For circuit reference, see appropriate wiring diagram in WIRING DIAGRAMS article.

For duplication of DTC, ensure

No active fuel trim, fuel injector circuit, misfire, EVAP system, EGR, AIR, TP, IAT, MAP, ECT, CKP, or MAF sensor DTCs are set.
DTCs P0131 or P0132 are not set.
System voltage is 9-18 volts.
IAT is less than 113°F (45°C) at start-up.
ECT is less than 104°F (40°C) at start-up.
ECT and IAT are within 27°F (15°C) of each other at start-up.
Average MAF for the sample period is less than 26 gm/s.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-introduction__on-board-diagnostic-obd-system-check) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Turn ignition off. Ensure engine and HO2S 1 is completely cool. Connect scan tool. Turn ignition on, with engine off and immediately record HO2S 1 sensor voltage. Continue to monitor voltage for 2 minutes. If voltage increases or decreases by 150 mV from recorded value, go to next step. If voltage is not as specified, go to step 4 .
Condition required to set this DTC is not present at this time. Check for faulty HO2S 1 and/or intermittent HO2S 1 circuit faults. Repair as necessary. After repairs, go to step 14 . If no problem is found, see «DIAGNOSTIC AIDS»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p0135-p0204) .
Turn ignition off. Disconnect HO2S 1. Connect test light between HO2S 1 heater ignition feed and ground circuits at HO2S 1 harness connector. Turn ignition on. If test light illuminates, go to next step. If test light does not illuminate, go to step 6 .
Remove test light. Using jumper wires, jumper HO2S 1 high and low signal circuits to ground. Monitor HO2S 1 voltage with scan tool. If voltage is less than 20 mV, go to step 8 . If voltage is not less than 20 mV, go to step 7 .
Using a test light connected to ground, probe HO2S 1 heater ignition feed circuit at HO2S 1 harness connector. If test light illuminates, go to step 9 . If test light does not illuminate, go to step 10 .
Turn ignition off. Remove jumper wires from HO2S 1. Disconnect PCM harness connector containing HO2S 1 high and low signal circuits. Measure resistance of HO2S 1 high and low signal circuits between HO2S 1 and PCM harness connectors. If resistance of each circuit is less than 5 ohms, go to step 12 . If resistance of either circuit is not less than 5 ohms, go to step 11 .
Replace HO2S 1. After repairs, go to step 14 .
Repair open HO2S 1 heater ground circuit. After repairs, go to step 14 .
Repair HO2S 1 heater ignition feed circuit. After repairs, go to step 14 .
Repair circuit with high resistance. After repairs, go to step 14 .
Check for poor PCM harness connections. Repair as necessary. After repairs, go to step 14 .
Replace PCM. Program replacement PCM using required equipment. After repairs, go to next step.
Turn ignition off. Ensure engine and HO2S 1 is completely cool. Connect scan tool. Turn ignition on, with engine off and immediately record HO2S 1 sensor voltage. Continue to monitor voltage for 2 minutes. If voltage increases or decreases by 150 mV from recorded value, go to next step. If voltage is not as specified, go to step 4 .
Using scan tool, select CAPTURE INFO, REVIEW INFO function. If any undiagnosed DTCs are displayed, go to applicable DTC test. If no undiagnosed DTCs are displayed, system is okay.

DTC P0135: HO2S HEATER CIRCUIT-SENSOR 1 (3.8L "C", "F", "G", "H" & "W" BODIES)

Note. For circuit reference, see appropriate wiring diagram in WIRING DIAGRAMS article.

PCM provides about 0.45 volt reference to HO2S 1. HO2S 1 sensor signal voltage varies from about one volt when exhaust is rich to about 0.1 volt when exhaust is lean. When ignition is turned on, battery voltage is supplied to HO2S 1 heater to provide for faster sensor warm-up, thus allowing sensor to become active in a shorter period of time. PCM reads amount of time necessary for sensor to become active after start-up. If PCM determines that too much time was required for HO2S 1 to become active, DTC P0135 will set.

For duplication of DTC, ensure

No EVAP system, misfire, fuel trim, fuel injector circuit, EGR pintle position, TP, IAT, MAP, ECT, CKP, or MAF sensor DTCs are set.
Engine is running.
System voltage is 9-16 volts.
ECT and IAT is less than 95°F (35°C) at start-up.
Difference between ECT and IAT is not greater than 11°F (6°C) at start-up.
Average MAF for sample period is less than 18 gm/s.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-introduction__on-board-diagnostic-obd-system-check) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Turn ignition on, with engine off. Using scan tool, read HO2S 1 voltage. If voltage is greater than 0.6 volt or less than 0.3 volt within 2 minutes, see «DIAGNOSTIC AIDS»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p0135-p0204) . If voltage is not greater than 0.6 volt or not less than 0.3 volt within 2 minutes, go to next step.
Inspect HO2S 1 ignition feed fuse. If fuse is open, go to step 15 . If fuse is okay, go to next step.
Disconnect HO2S 1 harness connector. Connect a test light between ground and HO2S 1 ignition feed circuit. If test light illuminates, go to next step. If test light does not illuminate, go to step 7 .
Connect test light between HO2S 1 harness connector ignition feed and heater ground circuits. If test light illuminates, go to next step. If test light does not illuminate, go to step 8 .
Allow HO2S 1 to cool down for at least 10 minutes. Using DVOM, measure resistance between ignition feed and heater ground circuits at HO2S 1. If resistance is 5-10 ohms, go to step 9 . If resistance is not 5-10 ohms, go to step 14 .
Repair open in HO2S 1 ignition feed circuit. After repairs, go to step 16 .
Repair open in HO2S 1 heater ground circuit. After repairs, go to step 16 .
Check for faulty connection at HO2S 1. Repair as necessary. After repairs, go to step 16 . If connection is okay, go to next step.
Turn ignition off. Disconnect PCM harness connectors. Measure resistance of HO2S 1 signal and ground circuits. If resistance on either circuit is greater than 5 ohms, repair open or faulty connection as necessary. After repairs, go to step 16 . If resistance is 5 ohms or less, go to next step.
Check for faulty connection at HO2S 1 harness connector. Repair as necessary. After repairs, go to step 16 . If connection is okay, go to next step.
Check for faulty HO2S 1 ground circuit connection at PCM. Repair as necessary. After repairs, go to step 16 . If connection is okay, go to next step.
Check for faulty HO2S 1 signal circuit connection at PCM. Repair as necessary. After repairs, go to step 16 . If connection is okay, go to next step.
Replace HO2S 1. After repairs, go to step 16 .
Locate and repair short to ground in HO2S 1 ignition feed circuit, and then replace fuse. After repairs, go to next step.
Allow engine to cool completely. Using scan tool, clear DTCs. Turn ignition on, engine off. Read HO2S 1 voltage. If voltage is greater than 0.6 volt or less than 0.3 volt within 2 minutes, system is okay. If voltage is not greater than 0.6 volt or less than 0.3 volt within 2 minutes, go to step 2 .

Check for faulty connections or damaged harness. If connections and harness appear okay, observe scan tool while moving all related harness and connectors. A change in scan tool display indicates fault location.

DTC P0135: HO2S HEATER CIRCUIT-BANK 1, SENSOR 1 (4.0L "G" BODY & 4.6L "E" & "K" BODIES)

Note. For circuit reference, see appropriate wiring diagram in WIRING DIAGRAMS article.

This test determines if the heating element in the rear oxygen sensor is working properly. Oxygen sensor voltage is produced when the sensor reaches operating temperature and when the oxygen content of the exhaust stream is different than that in the atmosphere. The heating element is energized through the ignition signal circuit, when ignition is turned on, allowing sensor to reach operating temperature quickly. This in turn allows the PCM to enter into "closed loop" quicker. The voltage that the PCM measures on the oxygen sensor high and low inputs is called bias voltage. When bias voltage takes too long to vary (greater or less than bias voltage) after ignition is turned on, DTC P0135 will set.

For duplication of DTC, ensure

DTCs P0101, P0102, P0103, P0117, P0118 and P0134 are not set.
ECT dropped at least 50°F (10°C) from end of the last ignition cycle to the beginning of this ignition cycle.
Ignition voltage is 11 volts or greater.
Average HO2S 1 bias voltage is 352-546 mV.
Engine did not stall during test.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-introduction__on-board-diagnostic-obd-system-check) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Turn ignition on, with engine off. Disconnect HO2S 1. Using DVOM, measure voltage between sensor harness connector terminals "C" and "D". If voltage reading is greater than 10.5 volts, go to next step. If voltage reading is not greater than 10.5 volts, go to step 4 .
Using jumper wire, jumper sensor connector terminal "C" to harness connector terminal "C". Set DVOM to amp scale. Connect DVOM in series with sensor terminal "D" to sensor harness connector terminal "D". If DVOM reads 0.9-1.5 amps, go to step 5 . If amperage is not as specified, go to next step.
Measure voltage from harness connector terminal "D" to ground. If reading is 10.5 volts or greater, go to step 6 . If reading is not 10.5 volts or greater, go to step 7 .
Using scan tool, select FREEZE FRAME data and operate vehicle under the same conditions which set the DTC. If DTC resets, diagnose using DTC P0133 test. If DTC does not reset, fault is not present. See «DIAGNOSTIC AIDS»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p0135-p0204) .
Repair open in HO2S 1 ground circuit.
Repair open or short to ground in HO2S 1 ignition feed circuit.
Replace HO2S 1.

An intermittent open in HO2S ignition signal circuit or ground circuit may cause DTC to set. A malfunctioning HO2S 1 may also set DTC. DO NOT solder oxygen sensor wires.

DTC P0135: HO2S HEATER CIRCUIT BANK 1, SENSOR 1 (4.3L, 5.0L, 5.7L & 7.4L "C", "G", "K", "L", "M", "P", "S" & "T" SERIES)

Note. For circuit reference, see appropriate wiring diagram in WIRING DIAGRAMS article.

VCM supplies a voltage of about.45 volt between HO2S signal and HO2S ground circuits. HO2S varies voltage from about one volt with rich exhaust to 0.1 volt with lean exhaust. HO2S produces no voltage and acts as an open circuit when temperature is less than 600°F (316°C). An open sensor circuit or a cold sensor causes open loop operation.

HO2S heater provides for faster sensor warm-up allowing sensor to become active in a shorter period of time and remain active during long extended idle. DTC determines if HO2S heater is operating properly by monitoring amount of time necessary for HO2S to become active after start-up. When bias voltage takes too long to vary (greater or less than bias voltage) after ignition is turned on, DTC P0135 will set.

For duplication of DTC, ensure system voltage is 11.7-17 volts, MAF is less than 35 gm/s. engine run time is greater than 2 seconds, ECT and IAT is less than 91°F (33°C), and difference between ECT and IAT is less than 41°F (5°C).

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-introduction__on-board-diagnostic-obd-system-check) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Ensure engine and HO2S 1 are completely cool. Install scan tool. Turn ignition on, with engine off. Immediately record HO2S 1 voltage with scan tool. Continue monitoring voltage for 2 minutes. If HO2S 1 voltage gradually increases or decreases by 150 mV from recorded value, go to next step. If HO2S 1 voltage is not as specified, go to step 4 .
Condition required to set this DTC is not present at this time. Check for faulty HO2S 1 and/or intermittent HO2S 1 circuit faults. Repair as necessary. After repairs, go to step 14 . If no problem is found, see «DIAGNOSTIC AIDS»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p0135-p0204) .
Turn ignition off. Disconnect HO2S 1 harness connector. Connect test light between HO2S 1 heater ignition feed and heater ground circuits at HO2S 1 harness connector. Turn ignition on. If test light illuminates, go to next step. If test light does not illuminate, go to step 6 .
Remove test light. Using jumper wires, jumper HO2S 1 high and low signal circuits to ground. Monitor HO2S 1 voltage with scan tool. If voltage is less than 20 mV, go to step 8 . If voltage is not less than 20 mV, go to step 7 .
Using a test light connected to ground, probe HO2S 1 heater ignition feed circuit. If test light illuminates, go to step 9 . If test light does not illuminate, go to step 10 .
Turn ignition off. Remove jumper wires. Disconnect VCM harness connector containing HO2S 1 high and low signal circuits. Measure resistance of HO2S 1 high and low signal circuits between HO2S 1 and VCM. If resistance of each circuit is less than 5 ohms, go to step 12 . If resistance of either circuit is not less than 5 ohms, go to step 11 .
Replace HO2S 1. After repairs, go to step 14 .
Repair open HO2S 1 heater ground circuit. After repairs, go to step 14 .
Repair loss of voltage on HO2S 1 heater ignition feed circuit. After repairs, go to step 14 .
Repair circuit with high resistance. After repairs, go to step 14 .
Check for faulty VCM harness connections. Repair as necessary. After repairs, go to step 14 . If connections are okay, go to next step.
Replace VCM. Program replacement VCM using required equipment. Perform Passlock® reprogramming and CKP system variation learn procedures. After repairs, go to next step.
Ensure engine and HO2S 1 are completely cool. Install scan tool. Turn ignition on, with engine off. Immediately record HO2S 1 voltage with scan tool. Continue monitoring voltage for 2 minutes. If HO2S 1 voltage gradually increases or decreases by 150 mV from recorded value, go to next step. If HO2S 1 voltage is not as specified, go to step 4 .
Using scan tool, select CAPTURE INFO, REVIEW INFO. If any undiagnosed DTCs are displayed, go to applicable DTC test. If not additional DTCs are displayed, system is okay.

An intermittent may be caused by a poor connection, rubbed-through wire insulation or a broken wire inside insulation. Inspect harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, poor terminal to wire connection, and damaged harness. DO NOT solder HO2S wires.

DTC P0135: HO2S HEATER CIRCUIT-BANK 1, SENSOR 1 (4.8L, 5.3L & 6.0L "C" & "K" SERIES)

Note. For circuit reference, see appropriate wiring diagram in WIRING DIAGRAMS article.

For duplication of DTC, ensure

DTCs P0101, P0102, P0103, P0112, P0113, P0117, P0118, P0121, P0122, P0123, P0125, P0200, P0335, P0336, P0351-P0358 or P1258 are not set.
IAT and ECT temperature are less than 122°F (50°C) and are within 46°F (8°C) of each other at start-up.
Ignition voltage is 10-18 volts.
AIR, EGR and catalyst diagnostics are not active.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-introduction__on-board-diagnostic-obd-system-check) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Ensure engine and HO2S 1 are completely cool. Turn ignition on. Using scan tool, monitor HO2S 1 voltage. If voltage changes from about 450 mV to less than 300 mV or greater than 700 mV, see «DIAGNOSTIC AIDS»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p0135-p0204) . If voltage does not change as specified, go to next step.
Check for open in fuse that supplies current to HO2S 1 heater circuit. If fuse is open, go to step 11 . If fuse is okay, go to next step.
Disconnect HO2S 1 harness connector. Using a test light connected to ground, probe HO2S 1 heater ignition feed circuit. If test light illuminates, go to next step. If test light does not illuminate, go to step 7 .
Connect test light between HO2S 1 heater ignition feed and heater ground circuits at HO2S 1 harness connector. If test light illuminates, go to next step. If test light does not illuminate, go to step 8 .
Measure resistance of HO2S 1 between heater ignition feed and heater ground circuits. If resistance is 3.5-14.0 ohms, go to step 9 . If resistance is not as specified, go to step 10 .
Repair open HO2S 1 heater ignition feed circuit. After repairs, go to step 12 .
Repair open HO2S 1 heater ground circuit. After repairs, go to step 12 .
Check for faulty HO2S 1 harness connections. Repair as necessary. After repairs, go to step 12 . If connections are okay, go to next step.
Replace HO2S 1. After repairs, go to step 12 .
Repair short to ground in HO2S 1 heater ignition feed circuit. Replace fuse. After repairs, go to next step.
Using scan tool, clear DTCs. Start engine and allow it to reach normal operating temperature. Operate vehicle under conditions required to set this DTC. If scan tool indicates this test ran and passed, go to next step. If scan tool does not indicate this test ran and passed, go to step 2 .
Using scan tool, select CAPTURE INFO, REVIEW INFO. If any undiagnosed DTCs are displayed, go to applicable DTC test. If not additional DTCs are displayed, system is okay.

DTC P0135: HO2S HEATER CIRCUIT-BANK 1, SENSOR 1 (5.7L "F" & "Y" BODIES)

Note. For circuit reference, see appropriate wiring diagram in WIRING DIAGRAMS article.

PCM supplies a bias voltage (about 450 mV) on HO2S signal high and low circuits. When ignition is turned on, battery voltage is supplied to HO2S heater. As heater reaches operating temperature, HO2S voltage responds by changing from a bias voltage range to normal operation (less than 300 mV). Depending on exhaust gas content, it is possible for HO2S voltage to increase to more than 450 mV.

PCM will run heater test only on a cold start and once during ignition cycle. When engine is started, PCM will determine how much time it takes HO2S voltage to go from above or below bias range threshold. If PCM detects that it took too much time to enter into normal operating range, DTC P0135 will set. The time it takes HO2S to reach operating temperature is based on amount of air that flows into engine.

For duplication of DTC, ensure

DTCs P0101, P0102, P0103, P0112, P0113, P0117, P0118, P0121, P0122, P0123, P0125, P0200, P0335, P0336, P0351-P0358 or P1258 are not set.
IAT and ECT are less than 122°F (50°C) and are within 46°F (8°C) of each other at start-up.
Ignition voltage is 10-18 volts.
AIR, EGR and catalyst diagnostics are not active.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-introduction__on-board-diagnostic-obd-system-check) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Turn ignition on, with engine off. Using scan tool, select ENGINE 1 DATA LIST and monitor HO2S 1 voltage. If HO2S 1 voltage changes from bias voltage to greater than 700 mV or less than 300 mV, see «DIAGNOSTIC AIDS»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p0135-p0204) . If HO2S voltage does not respond as indicated, go to next step.
Check HO2S 1 ignition feed fuse. If fuse is faulty, go to step 11 . If fuse is okay, go to next step.
Raise and support vehicle. Disconnect HO2S connector. Connect test light to chassis ground and probe ignition feed circuit at HO2S 1 harness connector. If test light illuminates, go to next step. If test light does not illuminate, go to step 7 .
Connect test light between ignition feed and heater ground circuits at HO2S 1 harness connector. If test light illuminates, go to next step. If test light does not illuminate, go to step 8 .
Using DVOM, measure resistance between ignition feed and heater ground circuits at HO2S 1. If resistance is 3.5-14.0 ohms, go to step 9 . If resistance is not as specified, go to step 10 .
Repair open in HO2S 1 ignition feed circuit. After repairs, go to step 12 .
Repair open in HO2S 1 heater ground circuit. After repairs, go to step 12 .
Check for poor terminal connection at HO2S 1 harness connector. Repair as necessary. After repairs, go to step 12 . If connections are okay, go to next step.
Replace HO2S 1. After repairs, go to step 12 .
Locate and repair short to ground in HO2S ignition feed circuit and replace fuse. After repairs, go to next step.
Using scan tool, clear DTCs. Start and warm engine to normal operating temperature. Select DTC, SPECIFIC, and then enter DTC P0135. Operate vehicle within conditions for setting this DTC. If scan tool indicates that this test ran and passed, go to next step. If scan tool does not indicate that this test ran and passed, go to step 2 .
Using scan tool, select CAPTURE INFO, REVIEW INFO function. If any undiagnosed DTCs are displayed, go to applicable DTC test. If no undiagnosed DTCs are displayed, system is okay.

Using FREEZE FRAME and/or FAILURE RECORDS data may aid in locating intermittent condition. If DTC cannot be duplicated, information included in this data can be useful in determining how many miles since DTC has set.

The FAIL COUNTER and PASS COUNTER can also be used to determine how many ignition cycles diagnostic reported a pass and/or fail condition. Operate vehicle within same freeze frame conditions (RPM, load, vehicle speed, temperature, etc.) that are noted. This will isolate when DTC failed.

The heater diagnostic will only run on a cold start and only once per ignition cycle. Oxygen supply inside HO2S is necessary for proper operation and is provided through HO2S wires. Check all HO2S wires and connections for breaks or contamination.

DTC P0136: HO2S CIRCUIT-BANK 1, SENSOR 2 (3.0L "V" BODY)

Note. For circuit reference, see appropriate wiring diagram in WIRING DIAGRAMS article.

Heated Oxygen Sensor (HO2S) is a wide range-type sensor that calculates amount of oxygen in exhaust stream more accurately than a toggling-type sensor. This HO2S operates more like an air fuel sensor. ECM supplies.28 volt to sensor and uses this voltage as a reference to amount of oxygen in exhaust system. When system is lean, oxygen level will be high and reference voltage will also be high. When oxygen level is low, reference voltage will also be low. ECM monitors variation in voltage and attempts to maintain voltage constant by increasing or decreasing amount of current flow to HO2S. Using this information allows ECM to maintain proper air/fuel ratio.

If ECM detects low HO2S voltage for an extended period of time, DTC P0136 will set. For duplication of DTC, ensure no EVAP system DTCs are set, rear HO2S are in closed loop, secondary AIR diagnostic is not running, engine is running, low fuel is not indicated, and battery voltage is greater than 11 volts.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-introduction__on-board-diagnostic-obd-system-check) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Start engine and run to normal operating temperature. Using scan tool, monitor HO2S 2 voltage. If HO2S 2 voltage on scan tool remains less than 399 mV, go to step 4 . If HO2S 2 voltage on scan tool does not remain less than 399 mV, go to next step.
Turn ignition on, with engine off. Review FREEZE FRAME data for this DTC and note parameters. Clear DTCs. Turn ignition off for 15 seconds. Start engine and operate vehicle as close to conditions recorded in FREEZE FRAME as possible. Check for DTCs. If DTC P0136 is set, go to next step. If DTC P0136 is not set, see «DIAGNOSTIC AIDS»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p0135-p0204) .
Turn ignition on, with engine off. Disconnect HO2S 2 connector. Check for signs of water or corrosion. Repair as necessary. If HO2S 2 voltage value on scan tool is 375-525 mV, go to step 14 . If HO2S 2 voltage value on scan tool is not 375-525 mV, go to next step.
Using DVOM, measure voltage between ground and signal circuit at HO2S 2 harness connector. If voltage is 900-1100 mV, go to next step. If voltage is not 900-1100 mV, go to step 11 .
Using DVOM, measure voltage between ground and low circuit at HO2S 2 harness connector. If voltage is 700-800 mV, go to step 22 . If voltage is not 700-800 mV, go to next step.
Continue to monitor voltage from HO2S 2 low circuit between harness connector and ground. Disconnect 3 other HO2S. As each sensor is disconnected, recheck voltage on DVOM. If disconnecting one of the other sensors restores voltage to 700-800 mV, go to step 14 . If disconnecting the other sensors does not restore voltage to 700-800 mV, go to next step.
Leave all HO2S disconnected. Turn ignition off. Disconnect ECM harness connectors located in engine compartment relay center. Turn ignition on. Using DVOM, measure voltage between ground and HO2S 2 low circuit at ECM harness connector. If any voltage is present, go to step 15 . If no voltage is present, go to next step.
Using DVOM, check harness continuity of HO2S 2 low circuit. If continuity is present, go to next step. If continuity is not present, go to step 16 .
Using DVOM, check harness continuity between HO2S 2 low circuit and ground. If continuity is present, go to step 17 . If continuity is not present, go to step 21 .
Leave all HO2S disconnected. Turn ignition off. Disconnect ECM harness connectors located in engine compartment relay center. Turn ignition on. Using DVOM, measure voltage between ground and HO2S 2 signal circuit at ECM harness connector. If any voltage is present, go to step 18 . If no voltage is present, go to next step.
Using DVOM, check harness continuity of HO2S 2 signal circuit. If continuity is present, go to next step. If continuity is not present, go to step 19 .
Using DVOM, check harness continuity between HO2S 2 signal circuit and ground. If continuity is present, go to step 20 . If continuity is not present, go to step 21 .
Replace shorted HO2S 2. After repairs, go to step 23 .
Repair short to voltage in HO2S 2 low circuit. After repairs, go to step 23 .
Repair open or high resistance in HO2S 2 low circuit. After repairs, go to step 23 .
Repair short to ground in HO2S 2 low circuit. After repairs, go to step 23 .
Repair short to voltage in HO2S 2 signal circuit. After repairs, go to step 23 .
Repair open or high resistance in HO2S 2 signal circuit. After repairs, go to step 23 .
Repair short to ground in HO2S 2 signal circuit. After repairs, go to step 23 .
Check for poor connections and terminal tension at ECM harness connectors. Repair as necessary. After repairs, go to step 23 . If connections and terminals are okay, go to next step.
Replace ECM. New ECM must be programmed with theft deterrent module frequency code currently on vehicle. After repairs, go to next step.
Using scan tool, clear DTCs. Turn ignition off for 15 seconds. Start engine and operate vehicle as close to conditions recorded in FREEZE FRAME as possible. Check for DTCs. If DTC P0136 is set, go to step 2 . If DTC P0136 is not set, go to next step.
If other DTCs were present during OBD system check and have not been diagnosed, go to applicable DTC. If no other DTCs are present, system is okay.

HO2S pigtail or harness may be mispositioned and contacting exhaust system. Inspect harness connectors for backed-out terminals, improper mating, broken locks, improperly formed or damaged terminals, poor terminal-to-wire connection, corrosion or water intrusion.

Inspect for poor ECM to engine grounds. If fuel pressure is too low, this DTC may set. Check for lean injectors. Inspect for disconnected or damaged vacuum hoses and for vacuum leaks at intake manifold, throttle body and crankcase ventilation system.

An exhaust leak may cause outside air to be pulled into exhaust gas stream past HO2S, causing this DTC to set. Check for exhaust leaks near HO2S.

Check for fuel contamination. Water, even in small amounts can be delivered to fuel injectors. Water can cause a lean condition to be indicated. Excessive alcohol in fuel can also cause this condition.

DTC P0137: HO2S CIRCUIT-LOW VOLTAGE-SENSOR 2 (1.9L SATURN)

Note. For circuit reference, see appropriate wiring diagram in WIRING DIAGRAMS article.

When the rear (No. 2) Heated Oxygen Sensor (HO2S) temperature reaches about 600°F (316°C), it becomes an electrical source that responds to the oxygen content in the exhaust. PCM produces a bias voltage of about 450 mV on the oxygen sensor circuit. When sensor is cold, its internal resistance is extremely high; therefore the PCM recognizes the bias as an open circuit. As the sensor warms up, the internal resistance decreases. When sensor reaches about 600°F (316°C), it starts producing a voltage based on the oxygen content in the exhaust stream.

DTC P0137 will set if HO2S 2 voltage is less than 25 mV for 100 seconds or when HO2S 2 voltage is less than 291 mV in the power enrichment mode for 30 seconds when system is in "closed loop" mode, no other engine sensor or misfire DTCs have been set or commanded air/fuel ratio is about 14.7:1. HO2S 2 signal is continuously monitored once these conditions are met.

Connect scan tool. Operate engine at 1500 RPM. Ensure ECT reading is greater than 140°F (60°C). Monitor HO2S 2 reading. If HO2S 2 reading is constantly less than 100 mV, go to next step. If HO2S 2 reading is not constantly less than 100 mV, problem is intermittent. See «DIAGNOSTIC AIDS»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p0135-p0204) .
Disconnect HO2S 2 harness connector. Check HO2S 2 reading. If HO2S 2 reading is 391-491 mV, replace sensor. If HO2S 2 reading is not 391-491 mV, go to next step.
Turn ignition off. Disconnect PCM harness connector J3. Using a test light connected to battery positive, probe HO2S 2 signal circuit terminal. If test light illuminates, check signal circuit for short to ground or shorted to HO2S 2 ground circuit. If test light does not illuminate, replace PCM.

Use scan tool to review malfunction history diagnostic information. This data can be used to duplicate a problem. If a front O2S DTC and a rear HO2S 2 DTC are set, diagnose the front O2S fault first. A diagnosed front O2S DTC may lead to a mechanical or fuel system failure which set the rear HO2S 2 DTC.

DTC P0137: HO2S CIRCUIT-LOW VOLTAGE-SENSOR 2 (2.2L "J" BODY, 2.2L "S" SERIES & 2.4L "J" & "N" BODIES)

Note. For circuit reference, see appropriate wiring diagram in WIRING DIAGRAMS article.

The Heated Oxygen Sensor 2 (HO2S 2), located rear of catalytic converter, produces an output signal relative to oxygen storage capacity of catalytic converter. HO2S 2 signal is less active than signal produced by front oxygen sensor. DTC P0137 will set if HO2S 2 voltage remains less than 22 mV for 150 seconds.

For duplication of DTC, ensure

DTCs P0105, P0107, P0108, P0112, P0113, P0117, P0118, P0122, P0123, P0171, P0200, P0300, P0301, P0302, P0303, P0304, P0335, P0440, P0442, P0446, P0506, P0507, P0601, P0602 or P1441 are not set.
Airflow is greater than 5.5 gm/s.
ECT is greater than 104°F (40°C).
TP sensor angle is 5-50 percent for 4 seconds.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-introduction__on-board-diagnostic-obd-system-check) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Turn ignition on, with engine off. Using scan tool, observe HO2S 2 voltage. If voltage is less than 200 mV, go to step 4 . If voltage is not less than 200 mV, go to next step.
Turn ignition on, with engine off. Using scan tool, review FREEZE FRAME data and note parameters. Start engine and operate vehicle within conditions required for setting this DTC, and as close to conditions recorded in FREEZE FRAME as possible. Using scan tool, observe HO2S 2 voltage. If voltage is less than 40 mV, go to next step. If voltage is not less than 40 mV, go to step 8 .
Turn ignition off. Disconnect HO2S 2 connector. Connect a jumper wire between ground and ground circuit terminal at HO2S 2 harness connector. Turn ignition on, with engine off. If voltage is 350-550 mV, go to step 7 . If voltage is not 350-550 mV, go to next step.
Turn ignition off. Disconnect PCM harness connectors. Check HO2S 2 signal circuit for a short to ground or a short to sensor ground circuit. Repair as necessary. After repairs, go to step 8 . If circuit is okay, go to next step.
Replace PCM. Program replacement PCM using required equipment. After repairs, go to step 8 .
Replace HO2S 2. After repairs, go to next step.
Using scan tool, clear DTCs. Start engine and allow it to idle. Ensure engine is at normal operating temperature. Operate vehicle within conditions required for setting this DTC. Select SPECIFIC DTC function, and then enter DTC P0137. If scan tool indicates this test ran and passed, go to next step. If scan tool does not indicate this test ran and passed, go to step 2 .
If any other DTCs are set, diagnose DTCs as necessary. If no other DTCs are set, system is okay.

Inspect exhaust system for leaks. Check oxygen sensor pigtail wire for breaks, contamination or grounding on exhaust manifold. Check for intermittent short to ground in HO2S 2 signal circuit wire. DO NOT attempt to repair damaged oxygen sensor connector or wiring. If damage is detected, replace oxygen sensor.

DTC P0137: HO2S CIRCUIT-LOW VOLTAGE-SENSOR 2 (3.1L "N" & "W" BODIES & 3.4L "N" BODY & "U" SERIES)

Note. For circuit reference, see appropriate wiring diagram in WIRING DIAGRAMS article.

Three-Way Catalyst (TWC) system is used to control emissions. PCM uses signal from Heated Oxygen Sensor 2 (HO2S 2) behind TWC to read efficiency of TWC. PCM will set DTC P0137 if TWC oxygen storage capacity is less than a predetermined threshold.

For duplication of DTC, ensure

No active misfire, fuel injector circuit, EVAP system, fuel trim, EGR system, TP, IAT, MAP, ECT, MAF or CKP sensor DTCs are set.
Closed loop commanded air/fuel ratio is 14.5-14.8:1.
Throttle angle is 3-40 percent.
HO2S 2 signal voltage remains less than 10 mV during normal closed loop operation.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-introduction__on-board-diagnostic-obd-system-check) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Start engine and allow it to reach operating temperature. Operate vehicle under conditions required to set DTC. Using scan tool, read HO2S 2 voltage. If voltage remains less than 100 mV, go to step 4 . If voltage is not specified, go to next step.
Turn engine off. Turn ignition on, engine off. Using scan tool, read and record FAILURE RECORDS data. Operate vehicle within conditions noted in FAILURE RECORDS data. Using scan tool, read SPECIFIC DTC. If scan tool displays DTC P0137 FAILED THIS IGN, go to next step. If scan tool does not display DTC P0137 FAILED THIS IGN, see «DIAGNOSTIC AIDS»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p0135-p0204) .
Disconnect HO2S 2 harness connector. Connect a jumper wire between HO2S 2 harness connector ground circuit and chassis ground. If voltage is about 450 mV, see «DIAGNOSTIC AIDS»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p0135-p0204) . If voltage is not as specified, go to next step.
Turn ignition off. Disconnect PCM harness connectors. Check HO2S 2 sensor harness connector signal circuit for short to ground or short to sensor ground. If short is found, go to next step. If circuit is okay, go to step 7 .
Repair circuit as necessary. After repairs, go to step 8 .
Replace PCM. Program replacement PCM using required equipment. After repairs, go to next step.
Turn ignition on, engine off. Using scan tool, read and record FAILURE RECORDS data, and clear DTCs. Operate vehicle within conditions noted in FAILURE RECORDS data. Using scan tool, select SPECIFIC DTC INFO for DTC P0137. If scan tool displays DTC P0137 FAILED THIS IGN, go to step 2 . If scan tool does not display DTC P0137 FAILED THIS IGN, system is okay.

Ensure HO2S 2 sensor harness is routed correctly and not contacting exhaust system. Check for faulty PCM grounds. Check fuel system. See BASIC FUEL SYSTEM CHECKS in appropriate BASIC DIAGNOSTIC PROCEDURES article. Perform injector balance test. See appropriate SYSTEM & COMPONENT TESTING article.

Check for vacuum leaks at intake manifold, throttle body, EGR system and crankcase ventilation system. Check for exhaust leaks in front of HO2S 2. Disconnect MAF sensor connector and see if lean condition is corrected. If lean condition is corrected, replace MAF sensor. Check for fuel contamination.

DTC P0137: HO2S CIRCUIT-LOW VOLTAGE-SENSOR 2 (3.8L "C", "F", "G", "H" & "W" BODIES)

Note. For circuit reference, see appropriate wiring diagram in WIRING DIAGRAMS article.

Three-Way Catalyst (TWC) system is used to control emissions. PCM uses signal from Heated Oxygen Sensor 2 (HO2S 2) located behind TWC to read efficiency of TWC. PCM will set DTC P0137 if TWC oxygen storage capacity is less than a predetermined threshold.

For duplication of DTC, ensure no EVAP system, EGR pintle position, misfire, fuel trim, fuel injector circuit, TP, IAT, MAP, ECT, CKP or MAF sensor DTCs are set, closed loop commanded air/fuel ratio is 14.5-14.8:1, and TP angle is 3-40 percent.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-introduction__on-board-diagnostic-obd-system-check) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Start engine and allow it to reach operating temperature. Operate vehicle under conditions required to set DTC. Using scan tool, read HO2S 2 voltage. If voltage remains less than 10 mV, go to step 4 . If voltage does not remain less than 10 mV, go to next step.
Turn ignition on, engine off. Using scan tool, read and record FAILURE RECORDS data. Operate vehicle within conditions noted in FAILURE RECORDS data. Using scan tool, read SPECIFIC DTC. If scan tool displays DTC P0137 FAILED THIS IGN, go to next step. If scan tool does not display DTC P0137 FAILED THIS IGN, see «DIAGNOSTIC AIDS»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p0135-p0204) .
Disconnect HO2S 2 harness connector. Connect a jumper wire between HO2S 2 harness connector ground circuit and chassis ground. If voltage is about 450 mV, see «DIAGNOSTIC AIDS»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p0135-p0204) . If voltage is not about 450 mV, go to next step.
Turn ignition off. Disconnect PCM harness connectors. Check HO2S 2 sensor harness connector signal circuit for short to ground or short to sensor ground. Repair as necessary. After repairs, go to step 7 . If circuit is okay, go to next step.
Replace PCM. Program replacement PCM using required equipment. After repairs, go to next step.
Turn ignition on, with engine off. Using scan tool, read and record FAILURE RECORDS data, and clear DTCs. Operate vehicle within conditions noted in FAILURE RECORDS data. Using scan tool, select SPECIFIC DTC INFO for DTC P0137. If scan tool displays DTC P0137 FAILED THIS IGN, go to step 2 . If scan tool does not display DTC P0137 FAILED THIS IGN, system is okay.

DTC P0137: HO2S CIRCUIT-LOW VOLTAGE-BANK 1, SENSOR 2 (4.8L, 5.3L & 6.0L "C" & "K" SERIES & 5.7L "F" & "Y" BODIES)

Note. For circuit reference, see appropriate wiring diagram in WIRING DIAGRAMS article.

PCM supplies about 450 millivolts (mV) between HO2S high and low signal circuits. The HO2S voltage ranges from about 1000 mV when exhaust is rich to about 10 mV when exhaust is lean. PCM monitors and stores sensor voltage information and evaluates voltage samples to determine amount of time sensor voltage is out of range. If PCM detects HO2S voltage is less than predetermined voltage, DTC P0137 will set.

For duplication of DTC, ensure

DTCs P0101, P0102, P0103, P0112, P0113, P0117, P0118, P0121, P0122, P0123, P0125, P0200, P0335, P0336, P0351-P0358 or P1258 are not set.
AIR, EGR and catalyst diagnostics not active.
Ignition voltage is greater than 9 volts.
Fuel system is operating in "closed loop".
Fuel trim learn is enabled.
TP sensor angle is between 2 and 70 percent.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-introduction__on-board-diagnostic-obd-system-check) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Start and warm engine to normal operating temperature. Operate vehicle under conditions required to set DTC. Using scan tool, select ENGINE 1 DATA LIST and monitor HO2S voltage. If HO2S 2 voltage is fixed less than 80 mV, go to step 4 . If HO2S voltage is not fixed less than 80 mV, go to next step.
Turn ignition on, with engine off. Using scan tool, review FREEZE FRAME and/or FAILURE RECORDS data and note parameters. Turn ignition off for about 15 seconds. Start engine and operate vehicle within conditions required for this diagnostic to run, and as close to conditions recorded in FREEZE FRAME/FAILURE RECORDS as possible. Select DTC function, and then enter DTC P0137. If scan tool indicates that this test failed this ignition, go to next step. If scan tool does not indicate that this test failed this ignition, see «DIAGNOSTIC AIDS»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p0135-p0204) .
Disconnect HO2S 2 connector. Connect a fused jumper wire between PCM connector (harness side), HO2S 2 low circuit and ground. If sensor voltage is 350-550 mV, see «DIAGNOSTIC AIDS»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p0135-p0204) . If sensor voltage is not 350-550 mV, go to next step.
Turn ignition off. Disconnect PCM harness connector C1. Check HO2S 2 signal circuit for short to ground or short to sensor ground circuit. Repair as necessary. After repairs, go to next step. If circuit(s) are okay, go to step 7 .
Repair HO2S 2 signal circuit. After repairs, go to step 8 .
Replace PCM. Program replacement PCM using required equipment. After repairs, go to next step.
Using scan tool, clear DTCs. Start and warm engine to normal operating temperature. Select DTC, SPECIFIC, and then enter DTC P0137. Operate vehicle within conditions for setting this DTC. If scan tool indicates that this test ran and passed, go to next step. If scan tool does not indicate that this test ran and passed, go to step 2 .
Using scan tool, select CAPTURE INFO, REVIEW INFO function. If any undiagnosed DTCs are displayed, go to applicable DTC test. If no undiagnosed DTCs are displayed, system is okay.

Check HO2S pigtail wire for breaks, contamination or grounding on exhaust manifold. Check for intermittent ground in signal wire between sensor connector and sensor.

Check for lean injector(s). Perform injector balance test. See appropriate SYSTEM & COMPONENT TESTING article. Check for fuel contamination, improper fuel pressure or exhaust leak, especially near HO2S. Check for vacuum or crankcase leak, causing a lean condition.

DTC P0137: HO2S CIRCUIT-LOW VOLTAGE-BANK 1, SENSOR 2 (5.0L, 5.7L & 7.4L "C", "G", "K" & "P" SERIES)

Note. For circuit reference, see appropriate wiring diagram in WIRING DIAGRAMS article.

VCM supplies a voltage of about.45 volt between HO2S 2 signal and HO2S 2 ground circuits. HO2S 2 varies voltage from about one volt with rich exhaust to.1 volt with lean exhaust. HO2S 2 produces no voltage and acts as an open circuit when temperature is less than 600°F (316°C). DTC P0137, DTC P0138, an open sensor circuit or a cold sensor causes open loop operation. DTC P0137 determines if HO2S 2 or circuit is shorted low by checking for a lean condition during steady throttle and power enrichment.

For duplication of DTC, ensure no misfire, EVAP system, TP, IAT, MAP, ECT or MAF sensor DTCs are set, no intrusive tests are in progress, no device control active, and system voltage is greater than 9 volts.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-introduction__on-board-diagnostic-obd-system-check) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Install scan tool. Warm engine to normal operating temperature. Place transmission in Park or Neutral. Apply parking brake. Increase engine speed to 1200 RPM. Using scan tool, monitor HO2S 2 voltage. If HO2S 2 voltage is fixed at less than 26 mV on 5.0L and 5.7L, or 86 mV on 7.4L, go to step 4 . If HO2S 2 voltage is not as specified, go to next step.
DTC is intermittent. If no additional DTCs are set, see «DIAGNOSTIC AIDS»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p0135-p0204) . If any additional DTCs are set, go to applicable DTC test.
Turn ignition off. Disconnect HO2S 2 harness connector. Connect a jumper wire between ground and low circuit at HO2S 2 harness connector. Turn ignition on, with engine off. Monitor HO2S 2 voltage using scan tool. If voltage is 351-551 mV, go to next step. If voltage is not 351-551 mV, go to step 6 .
Check for conditions causing sensor to detect a lean condition (exhaust leaks, vacuum leaks, fuel system, etc.). Repair as necessary. After repairs, go to step 10 . If no problem is found, go to step 8 .
Turn ignition off. Remove jumper wire. Disconnect VCM harness connector containing HO2S 2 high signal circuit. Measure resistance between HO2S 2 high signal circuit and ground, and then between HO2S 2 high signal circuit and HO2S 2 low circuit. If resistance is infinite for both measurements, go to step 9 . If resistance is not infinite for both measurements, go to next step.
Repair HO2S 2 high signal circuit for short to ground or short to HO2S 2 low circuit. After repairs, go to step 10 .
Replace HO2S 2. After repairs, go to step 10 .
Replace VCM. Program replacement VCM using required equipment. Perform Passlock® reprogramming and CKP system variation learn procedures. After repairs, go to next step.
Using scan tool, clear DTCs. Start and warm engine to normal operating temperature. Select DTC, SPECIFIC, and then enter this DTC. Operate vehicle within the conditions for setting this DTC. If scan tool indicates that this test ran and passed, go to next step. If scan tool does not indicate that this test ran and passed, go to step 2 .
Using scan tool, select CAPTURE INFO, REVIEW INFO. If any undiagnosed DTCs are displayed, go to applicable DTC test. If no undiagnosed DTCs are displayed, system is okay.

Using scan tool, observe Long Term (LT) fuel trim values at different RPM and air flow conditions. Scan tool should display fuel trim cells so that LT fuel trim values can be check in each cell to determine when DTC may have set. If DTC is set, LT fuel trim values will be about 158 or greater.

Check for mispositioned HO2S 2 wire pigtail contacting exhaust manifold. Check for intermittent ground in wire between connector and sensor. Check for poor VCM to engine block ground. Check for lean fuel injectors. Check for water near in-tank fuel pump inlet that may be delivered to injectors. Water causes a lean exhaust and can cause DTC to set.

System will be lean if fuel pressure is too low. Monitor fuel pressure while driving vehicle at various speeds and loads to verify pressure. Check for an exhaust leak that can cause outside air to be pulled into exhaust and past sensor. Check for vacuum or crankcase leaks that can cause a lean condition and possibly high idle. If all above checks are okay, HO2S 2 is faulty. DO NOT solder HO2S 2 wires.

DTC P0138: HO2S CIRCUIT-VOLTAGE HIGH-SENSOR 2 (1.9L SATURN)

Note. For circuit reference, see appropriate wiring diagram in WIRING DIAGRAMS article.

When Heated Oxygen Sensor 2 (HO2S 2) temperature reaches about 600°F (316°C), it becomes an electrical source that responds to the oxygen content in the exhaust. PCM produces a bias voltage of about 450 mV on the oxygen sensor circuit. When sensor is cold, its internal resistance is extremely high, therefore the PCM recognizes the bias as an open circuit. As the sensor warms up, the internal resistance decreases. When sensor reaches about 600°F (316°C), it starts producing a voltage based on the oxygen content in the exhaust stream.

DTC P0138 will set if HO2S 2 voltage is greater than 1.065 volts for 100 seconds or when HO2S 2 voltage is greater than 587 mV in the decel fuel cut-off mode for 30 seconds when system is in "closed loop" mode, no other engine sensor or misfire DTCs have been set or commanded air/fuel ratio is about 14.7:1. HO2S 2 signal is continuously monitored once these conditions are met.

Connect scan tool. Operate engine at 1500 RPM. Ensure ECT reading is greater than 140°F (60°C). Monitor HO2S 2 reading. If HO2S 2 reading is constantly greater than 900 mV, go to next step. If HO2S 2 reading is not constantly greater than 900 mV, problem is intermittent. See «DIAGNOSTIC AIDS»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p0135-p0204) .
Disconnect HO2S 2 harness connector. Check HO2S 2 reading. If HO2S 2 reading is 391-491 mV, check sensor heater circuit for short to ground or replace faulty sensor. If HO2S 2 reading is not 391-491 mV, go to next step.
Using DVOM, measure voltage on HO2S 2 high signal circuit at sensor harness connector. If voltage is greater than 750 mV, high signal circuit is shorted to voltage. If voltage is not greater than 750 mV, terminal connections or PCM are faulty.

DTC P0138: HO2S CIRCUIT-VOLTAGE HIGH-SENSOR 2 (2.2L "J" BODY, 2.2L "S" SERIES & 2.4L "J" & "N" BODIES)

Note. For circuit reference, see appropriate wiring diagram in WIRING DIAGRAMS article.

The Heated Oxygen Sensor 2 (HO2S 2), located at rear of catalytic converter, produces an output signal relative to oxygen storage capacity of catalytic converter. HO2S 2 signal is less active than signal produced by front oxygen sensor. If HO2S 2 voltage remains greater than 1042 mV for 50-75 seconds, DTC P0138 will set.

For duplication of DTC, ensure

DTCs P0105, P0107, P0108, P0112, P0113, P0117, P0118, P0122, P0123, P0171, P0200, P0300, P0301, P0302, P0303, P0304, P0335, P0440, P0442, P0446, P0506, P0507, P0601, P0602 or P1441 are not set.
Airflow is greater than 5.5 gm/s.
ECT is greater than 104°F (40°C).
TP sensor angle is 5-50 percent for 4 seconds.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-introduction__on-board-diagnostic-obd-system-check) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Turn ignition on, with engine off. Using scan tool, observe HO2S 2 voltage. If voltage is greater than 1042 mV, go to step 4 . If voltage is not greater than 1042 mV, go to next step.
Turn ignition on, with engine off. Using scan tool, review FREEZE FRAME data and note parameters. Start engine and operate vehicle within conditions required for setting this DTC, and as close to conditions recorded in FREEZE FRAME as possible. Using scan tool, observe HO2S 2 voltage. If voltage is greater than 1042 mV, go to next step. If voltage is not greater than 1042 mV, go to step 9 .
Turn ignition off. Disconnect HO2S 2 harness connector. Disconnect PCM harness connectors. Using a DVOM, measure voltage between ground and signal circuit terminal at HO2S 2 harness connector. If voltage is zero volts, go to next step. If voltage is not zero volts, go to step 6 .
Reconnect PCM harness connectors. Turn ignition on, engine off. Using a jumper wire, jumper HO2S 2 ground circuit and signal circuit to ground. If voltage is less than 100 mV, go to step 7 . If measured voltage is not less than 100 mV, go to step 8 .
Repair short to voltage in HO2S 2 signal circuit. After repairs, go to step 9 .
Replace HO2S 2. After repairs, go to step 9 .
Replace PCM. Program replacement PCM using required equipment. After repairs, go to next step.
Using scan tool, clear DTCs. Start engine and allow it to idle. Ensure engine is at normal operating temperature. Operate vehicle within conditions required for setting this DTC. Select SPECIFIC DTC function, and then enter DTC P0138. If scan tool indicates this test ran and passed, go to next step. If scan tool does not indicate this test ran and passed, go to step 2 .
If any other DTCs are set, diagnose DTCs as necessary. If no other DTCs are set, system is okay.

Check oxygen sensor pigtail wire for breaks and contamination. Check for intermittent short to voltage in HO2S 2 ground circuit wire. DO NOT attempt to repair damaged oxygen sensor connector or wiring. If damage is detected, replace oxygen sensor. Check for an overly rich condition or contaminated HO2S 2.

DTC P0138: HO2S CIRCUIT-HIGH VOLTAGE-BANK 1, SENSOR 2 (3.0L "V" BODY)

Note. For circuit reference, see appropriate wiring diagram in WIRING DIAGRAMS article.

Heated Oxygen Sensor 2 (HO2S 2) is a wide range-type sensor that calculates amount of oxygen in exhaust stream more accurately than a toggling-type sensor. This HO2S operates more like an air fuel sensor. ECM supplies.28 volt to sensor and uses this voltage as a reference to amount of oxygen in exhaust system. When system is lean, oxygen level will be high and reference voltage will also be high. When oxygen level is low, reference voltage will also be low. ECM monitors variation in voltage and attempts to maintain voltage constant by increasing or decreasing amount of current flow to HO2S 2. Using this information allows ECM to maintain proper air/fuel ratio.

If ECM detects that HO2S 2 voltage is greater than 1.08 volts for more than.5 second, DTC P0138 will set. For duplication of DTC, ensure engine is running and battery voltage is greater than 11 volts.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-introduction__on-board-diagnostic-obd-system-check) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Start and warm engine to normal operating temperature. Using scan tool, monitor HO2S 2 voltage. If voltage remains greater than 1083 mV, go to step 4 . If voltage does not remain greater than 1083 mV, go to next step.
Turn ignition on, with engine off. Review FREEZE FRAME data for this DTC and note parameters. Clear DTCs. Turn ignition off for 15 seconds. Operate vehicle as close to conditions recorded in FREEZE FRAME as possible. Check for DTCs. If DTC P0138 is set, go to next step. If DTC P0138 is not set, see «DIAGNOSTIC AIDS»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p0135-p0204) .
Turn ignition on, with engine off. Disconnect HO2S 2 harness connector. Check for signs of water or corrosion. Observe HO2S 2 voltage on scan tool. If voltage is 375-525 mV, go to step 14 . If voltage is not 375-525 mV, go to next step.
Measure voltage between ground and signal circuit at HO2S 2 harness connector. If voltage is 900-1200 mV, go to next step. If voltage is not 900-1200 mV, go to step 11 .
Measure voltage between ground and low circuit at HO2S 2 harness connector. If voltage is 700-800 mV, go to step 22 . If voltage is not 700-800 mV, go to next step.
Continue to monitor voltage on HO2S 2 low circuit between harness connector and ground. Disconnect the 3 other HO2S harness connectors. As each sensor is disconnected, recheck voltage on DVOM. If disconnecting the other sensors restores voltage to 700-800 mV, go to step 14 . If disconnecting the other sensors does not restore voltage to 700-800 mV, go to next step.
Leave all HO2S 2 harness connectors disconnected. Turn ignition off. Disconnect ECM harness connectors. Turn ignition on. Measure voltage between ground and HO2S 2 low circuit at ECM harness connector. If any voltage is present, go to step 15 . If no voltage is present, go to next step.
Check for continuity in HO2S 2 low circuit between ECM and HO2S 2. If continuity is present, go to next step. If continuity is not present, go to step 16 .
Check for continuity between HO2S 2 low circuit and ground. If continuity is present, go to step 17 . If continuity is not present, go to step 21 .
Leave HO2S 2 disconnected. Turn ignition off. Disconnect ECM harness connectors located in engine compartment relay center. Turn ignition on. Check for voltage between ground and HO2S 2 signal circuit at ECM harness connector. If any voltage is present, go to step 18 . If no voltage is present, go to next step.
Check for continuity in HO2S 2 signal circuit between ECM and HO2S 2. If continuity is present, go to next step. If continuity is not present, go to step 19 .
Check for continuity between HO2S signal circuit and ground. If continuity is present, go to step 20 . If continuity is not present, go to step 21 .
Replace shorted HO2S 2. After repairs, go to step 23 .
Repair short to voltage in HO2S 2 low circuit. After repairs, go to step 23 .
Repair open or high resistance in HO2S 2 low circuit. After repairs, go to step 23 .
Repair short to ground in HO2S 2 low circuit. After repairs, go to step 23 .
Repair short to voltage in HO2S 2 signal circuit. After repairs, go to step 23 .
Repair open or high resistance in HO2S 2 signal circuit. After repairs, go to step 23 .
Repair short to ground in HO2S 2 signal circuit. After repairs, go to step 23 .
Check for poor connections and terminal tension at ECM harness connectors. Repair as necessary. After repairs, go to step 23 . If connections and terminals are okay, go to next step.
Replace ECM. New ECM must be programmed with theft deterrent module frequency code currently on vehicle. After repairs, go to next step.
Using scan tool, clear DTCs. Turn ignition off for 15 seconds. Start engine and operate vehicle as close to conditions recorded in FREEZE FRAME as possible. Check for DTCs. If DTC P0138 is set, go to step 2 . If DTC P0138 is not set, go to next step.
If other DTCs were present during OBD system check and have not been diagnosed, go to applicable DTC. If no other DTCs are present, system is okay.

HO2S 2 pigtail or harness may be mispositioned and contacting exhaust system. Inspect harness connectors for backed-out terminals, improper mating, broken locks, improperly formed or damaged terminals, poor terminal-to-wire connection, corrosion or water intrusion.

An oxygen supply inside HO2S 2 is necessary for proper operation. This supply of oxygen is provided through HO2S 2 wiring harness. All HO2S 2 wires and connections should be inspected for breaks or contamination. Repair as necessary. Inspect for poor ECM to engine ground connection.

DTC P0138: HO2S CIRCUIT-HIGH VOLTAGE-SENSOR 2 (3.1L "N" & "W" BODIES & 3.4L "N" BODY & "U" SERIES)

Note. For circuit reference, see appropriate wiring diagram in WIRING DIAGRAMS article.

The Heated Oxygen Sensor 2 (HO2S 2), located at rear of catalytic converter, produces an output signal relative to oxygen storage capacity of catalytic converter. HO2S 2 signal is less active than signal produced by front oxygen sensor. If HO2S 2 signal voltage remains excessively high for an extended period of time, DTC P0138 will set.

For duplication of DTC, ensure

No active misfire, fuel injector circuit, TP sensor, EVAP, IAT sensor, MAP sensor, fuel trim, EGR, ECT sensor, MAF sensor or CKP sensor DTCs are set.
Engine coolant temperature is greater than 149°F (65°C).
TP sensor angle is 3-40 percent.
Closed loop commanded air/fuel ratio is 14.5-14.8:1.
HO2S 2 signal voltage remains greater than 999 mV during normal closed loop operation, or greater than 200 mV during deceleration fuel mode operation.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-introduction__on-board-diagnostic-obd-system-check) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Start engine and allow it to reach normal operating temperature. Operate vehicle under conditions required to set DTC. Using scan tool, monitor HO2S 2 voltage. If voltage remains greater than 999 mV, go to step 4 . If voltage does not remain greater than 999 mV, go to next step.
Turn ignition on, with engine off. Using scan tool, review FREEZE FRAME data and note parameters. Start engine and operate vehicle within conditions required for setting this DTC, and as close to conditions recorded in FREEZE FRAME as possible. Monitor SPECIFIC DTC info for DTC P0138 until DTC P0138 test runs. If scan tool indicates test failed this ignition, go to next step. If scan tool does not indicated test failed this ignition, see «DIAGNOSTIC AIDS»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p0135-p0204) .
Disconnect HO2S 2 harness connector. Connect a jumper wire between ground and sensor ground circuit terminal at HO2S 2 harness connector. If voltage is about 450 mV, see «DIAGNOSTIC AIDS»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p0135-p0204) . If voltage is not about 450 mV, go to next step.
Turn ignition off. Disconnect PCM harness connector. Turn ignition on. Measure voltage between ground and HO2S 2 signal circuit terminal at PCM harness connector. If voltage is greater than 999 mV, go to next step. If voltage is not greater than 999 mV, go to step 7 .
Repair short to voltage in HO2S 2 signal circuit. After repairs, go to step 8 .
Replace PCM. Program replacement PCM using required equipment. After repairs, go to next step.
Using scan tool, clear DTCs. Turn ignition on, with engine off. Using scan tool, review FREEZE FRAME data and note parameters. Start engine and operate vehicle within conditions required for setting this DTC, and as close to conditions recorded in FREEZE FRAME as possible. Monitor SPECIFIC DTC info for DTC P0138 until DTC P0138 test runs. If scan tool indicates test failed this ignition, go to step 2 . If scan tool does not indicate test failed this ignition, system is okay.

Check if fuel pressure is too high. PCM can compensate for some increase; however, if fuel pressure is too high, DTC will set. Check for leaking injector(s) or faulty fuel pressure regulator. See appropriate SYSTEM & COMPONENT TESTING article. Check EVAP system for fuel saturation. Check MAF sensor. Check oxygen sensor for silicone contamination. Check TP sensor. See appropriate SYSTEM & COMPONENT TESTING article.

DTC P0138: HO2S CIRCUIT-HIGH VOLTAGE-SENSOR 2 (3.8L "C", "F", "G", "H" & "W" BODIES)

Note. For circuit reference, see appropriate wiring diagram in WIRING DIAGRAMS article.

For duplication of DTC, ensure no active EVAP system, misfire, fuel trim, fuel injector circuit, EGR pintle position, TP, IAT, MAP, ECT, CKP or MAF sensor DTCs are set, closed loop commanded air/fuel ratio is 14.5-14.8:1, and throttle angle is 3-40 percent.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-introduction__on-board-diagnostic-obd-system-check) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Start engine and allow it to reach normal operating temperature. Operate vehicle under conditions required to set DTC. Using scan tool, read HO2S 2 voltage. If voltage remains greater than 999 mV, go to step 4 . If voltage does not remain greater than 999 mV, go to next step.
Turn ignition on. Using scan tool, read and record FAILURE RECORDS data. Operate vehicle within conditions noted in FAILURE RECORDS data. Using scan tool, select SPECIFIC DTC INFO for DTC P0138. If scan tool displays DTC P0138 FAILED THIS IGN, go to next step. If scan tool does not display DTC P0138 FAILED THIS IGN, see «DIAGNOSTIC AIDS»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p0135-p0204) .
Disconnect HO2S 2 harness connector. Connect a jumper wire between HO2S 2 harness connector ground circuit and chassis ground. If voltage is about 450 mV, see «DIAGNOSTIC AIDS»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p0135-p0204) . If voltage is not about 450 mV, go to next step.
Turn ignition off. Disconnect PCM harness connectors. Turn ignition on. Using DVOM, measure voltage between PCM harness connector HO2S 2 signal circuit and chassis ground. If voltage is greater than 999 mV, go to next step. If voltage is not greater than 999 mV, go to step 7 .
Repair short to voltage in HO2S 2 signal circuit. After repairs, go to step 8 .
Replace PCM. Program replacement PCM using required equipment. After repairs, go to next step.
Turn ignition on, engine off. Using scan tool, read and record FAILURE RECORDS data, and clear DTCs. Operate vehicle within conditions noted in FAILURE RECORDS data. Using scan tool, select SPECIFIC DTC INFO for DTC P0138. If scan tool displays DTC P0138 FAILED THIS IGN, go to step 2 . If scan tool does not display DTC P0138 FAILED THIS IGN, system is okay.

Ensure HO2S 2 sensor harness is routed correctly and not contacting exhaust system. Check for open or short in HO2S 2 signal or ground circuits. Check for internally shorted HO2S 2. Check HO2S 2 for silicone (powdery white deposit) contamination. Check for faulty PCM grounds. Check fuel system. See BASIC FUEL SYSTEM CHECKS in appropriate BASIC DIAGNOSTIC PROCEDURES article. Perform injector balance test. See appropriate SYSTEM & COMPONENT TESTING article.

Check EVAP canister for fuel saturation. Disconnect MAF sensor connector and see if rich condition is corrected. If rich condition is corrected, replace MAF sensor. Check for fuel in fuel pressure regulator vacuum line.

DTC P0138: HO2S CIRCUIT-HIGH VOLTAGE-BANK 1, SENSOR 2 (4.3L "C" & "K" SERIES)

Note. For circuit reference, see appropriate wiring diagram in WIRING DIAGRAMS article.

Three-Way Catalyst (TWC) system is used to control emissions. VCM uses signal from Heated Oxygen Sensor 2 (HO2S 2) behind TWC to read efficiency of TWC. VCM will set DTC P0137 if TWC oxygen storage capacity is less than a predetermined threshold.

For duplication of DTC, ensure no active EVAP system, TP, IAT, MAP, ECT or MAF sensor DTCs are set, no intrusive tests are in progress, no device controls are active, and system voltage is 11.7-18 volts.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-introduction__on-board-diagnostic-obd-system-check) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Start engine and allow it to reach normal operating temperature. Using scan tool, read HO2S 2 voltage. If voltage remains greater than 994 mV, go to step 4 . If voltage does not remain greater than 994 mV, go to next step.
DTC is intermittent. If any additional DTCs are set, go to applicable DTC test. If no other DTCs are set, see «DIAGNOSTIC AIDS»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p0135-p0204) .
Turn ignition off. Disconnect HO2S 2 harness connector. Using a jumper wire, jumper HO2S 2 low circuit to ground. Turn ignition on. Monitor HO2S 2 voltage with scan tool. If voltage is 351-551 mV, go to next step. If voltage is not 351-551 mV, go to step 6 .
HO2S 2 is detecting a rich exhaust condition. Check for contaminated HO2S 2 or any conditions causing a rich condition. Repair as necessary. After repairs, go to step 10 . If no problem is found, go to step 8 .
Turn ignition off. Remove jumper wire. Disconnect VCM harness connector containing HO2S 2 high signal circuit. Turn ignition on. Measure voltage between ground and HO2S 2 high signal circuit at VCM harness connector. If voltage is greater than 20 mV, go to next step. If voltage is not greater than 20 mV, go to step 9 .
Repair short to voltage in HO2S 2 high signal circuit. After repairs, go to step 10 .
Replace HO2S 2. After repairs, go to step 10 .
Replace VCM. Program replacement VCM using required equipment. Perform Passlock® reprogramming and CKP variation learn procedures. After repairs, go to next step.
Using scan tool, clear DTCs. Start engine and operate vehicle under conditions required to set DTC. If scan tool indicates this test ran and passed, go to next step. If scan tool does not indicate this test ran and passed, go to step 2 .
If scan tool displays any additional undiagnosed DTCs, go to applicable DTC test. If scan tool does not display any additional undiagnosed DTCs, system is okay.

Ensure HO2S 2 sensor harness is routed correctly and not contacting exhaust system. Check for open or short in HO2S 2 signal or ground circuits. Check for internally shorted HO2S 2. Check HO2S 2 for silicone (powdery white deposit) contamination. Check for faulty VCM grounds. Check fuel system. See BASIC FUEL SYSTEM CHECKS in appropriate BASIC DIAGNOSTIC PROCEDURES article. Perform injector balance test. See appropriate SYSTEM & COMPONENT TESTING article.

DTC P0138: HO2S CIRCUIT-HIGH VOLTAGE-BANK 1, SENSOR 2 (4.8L, 5.3L & 6.0L "C" & "K" SERIES)

Note. For circuit reference, see appropriate wiring diagram in WIRING DIAGRAMS article.

For duplication of DTC, ensure

DTCs P0101, P0102, P0103, P0112, P0113, P0117, P0118, P0121, P0122, P0123, P0125, P0200, P0335, P0336, P0351-P0358 and P1258 are not set.
Ignition voltage is greater than 9 volts.
Fuel system is operating in closed loop.
AIR, EGR and catalyst diagnostics are not active.
Deceleration fuel cut-off mode is enabled for more than 3 seconds.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-introduction__on-board-diagnostic-obd-system-check) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Start engine and allow it to reach normal operating temperature. Increase engine speed to 1200 RPM. Monitor HO2S 2 voltage on scan tool. If voltage is greater than 930 mV, go to step 4 . If voltage is not greater than 930 mV, go to next step.
Turn ignition on, with engine off. Using scan tool, review FREEZE FRAME data and note parameters. Turn ignition off for 15 seconds. Start engine and operate vehicle within conditions required for setting this DTC, and as close to conditions recorded in FREEZE FRAME as possible. Monitor SPECIFIC DTC info for DTC P0138 until DTC P0138 test runs. If scan tool indicates test failed this ignition, go to next step. If scan tool does not indicated test failed this ignition, see «DIAGNOSTIC AIDS»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p0135-p0204) .
Turn ignition on, with engine off. Monitor HO2S 2 voltage with scan tool. If voltage is greater than 930 mV, go to next step. If voltage is not greater than 930 mV, see «DIAGNOSTIC AIDS»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p0135-p0204) .
Remove HO2S 2 heater fuse while monitoring HO2S 2 voltage. If voltage drops to 350-550 mV, go to next step. If voltage does not drop to 350-550 mV, go to step 7 .
Reinstall fuse. Disconnect HO2S 2 harness connector. Using a jumper wire, jumper HO2S 2 low circuit to ground. Monitor HO2S 2 voltage on scan tool. If voltage is 350-550 mV, go to step 10 . If voltage is not 350-550 mV, go to step 8 .
Turn ignition off. Disconnect PCM harness connector C1. Disconnect HO2S 2 harness connector. Turn ignition on. Check for voltage on HO2S 2 signal circuit at PCM harness connector. If any voltage is present, go to next step. If no voltage is present, go to step 9 .
Repair short to voltage in HO2S 2 signal circuit. After repairs, go to step 11 .
Replace PCM. Program replacement PCM using required equipment. After repairs, go to step 11 .
Replace HO2S 2. After repairs, go to next step.
Using scan tool, clear DTCs. Start engine and operate vehicle under conditions required to set DTC. If scan tool indicates this test ran and passed, go to next step. If scan tool does not indicate this test ran and passed, go to step 2 .
If scan tool displays any additional undiagnosed DTCs, go to applicable DTC test. If scan tool does not display any additional undiagnosed DTCs, system is okay.

DTC P0138: HO2S CIRCUIT-HIGH VOLTAGE-BANK 1, SENSOR 2 (5.0L, 5.7L & 7.4L "C", "G", "K" & "P" SERIES)

Note. For circuit reference, see appropriate wiring diagram in WIRING DIAGRAMS article.

VCM supplies a voltage of about.45 volt between HO2S 2 signal and HO2S 2 ground circuits. HO2S 2 varies voltage from about one volt with rich exhaust to 0.1 volt with lean exhaust. HO2S 2 produces no voltage and acts as an open circuit when temperature is less than 392°F (200°C). DTC P0138 determines if HO2S 2 or circuit is shorted high by checking for a rich condition during steady throttle.

For duplication of DTC, ensure

No misfire, EVAP system, ECT, IAT, MAF, MAP or TP sensor DTCs are set.
No intrusive tests are in progress.
No device controls are active.
System voltage is greater than 9 volts.
System is operating in closed loop.
Air/fuel ratio is 14.5-14.8:1.
Throttle position is 0-50 percent.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-introduction__on-board-diagnostic-obd-system-check) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Warm engine to normal operating temperature. Place gear selector in Park or Neutral. Apply parking brake. Increase engine speed to 1200 RPM. Monitor HO2S 2 voltage using scan tool. If voltage is fixed at greater than 994 mV on 5.0L and 5.7L, or 976 mV on 7.4L, go to next step. If voltage is not as specified, go to step 4 .
DTC is intermittent. If no additional DTCs are set, see «DIAGNOSTIC AIDS»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p0135-p0204) . If any additional DTCs are set, diagnose affected DTCs.
Turn ignition off. Disconnect HO2S 2 connector. Using a jumper wire, jumper HO2S 2 low circuit to ground. Turn ignition on, with engine off. Monitor HO2S 2 voltage with scan tool. If voltage is 351-551 mV, go to next step. If HO2S 2 voltage is not 351-551 mV, go to step 6 .
HO2S 2 is detecting a rich condition. Check for contaminated HO2S 2 or conditions causing sensor to detect a rich condition. Repair as necessary. After repairs, go to step 10 . If no problem is found, go to step 8 .
Turn ignition off. Remove jumper wire. Disconnect VCM harness connector containing HO2S 2 high signal circuit. Turn ignition on, with engine off. Measure voltage between ground and HO2S 2 high signal circuit at VCM harness connector. If voltage is greater than 20 mV, go to next step. If voltage is not greater than 20 mV, go to step 9 .
Repair short to voltage in HO2S 2 high signal circuit. After repairs, go to step 10 .
Replace HO2S 2. After repairs, go to step 10 .
Replace VCM. Program replacement VCM using required equipment. Perform Passlock® reprogramming and CKP system variation learn procedures. After repairs, go to next step.
Using scan tool, clear DTCs. Start and warm engine to normal operating temperature. Select DTC, SPECIFIC, and then enter this DTC. Operate vehicle within the conditions for setting this DTC. If scan tool indicates that this test ran and passed, go to next step. If scan tool does not indicate that this test ran and passed, go to step 2 .
Using scan tool, select CAPTURE INFO, REVIEW INFO. If any undiagnosed DTCs are displayed, go to applicable DTC test. If no additional DTCs are displayed, system is okay.

System will be rich if fuel pressure is too high. VCM can compensate for some increase in fuel pressure, but if pressure is too high, DTC may set. Check for rich or leaking injector. Check for fuel contaminated oil. Check for fuel saturation in EVAP canister purge. If full of fuel, check canister control and hoses. Check for leaking fuel pressure regulator diaphragm by checking vacuum line to regulator for fuel.

Check for an intermittent TP sensor output that will cause system to go rich due to false indication of throttle moving. Check for false rich indication due to silicone contamination of HO2S 2 indicated by DTC accompanied by lean driveability conditions and a powdery white deposit on sensor.

Check for internally shorted HO2S 2 as indicated by a voltage of greater than one volt on scan tool. Disconnect HO2S 2. If voltage changes from greater than one volt to about.45 volt, replace HO2S 2. DO NOT solder HO2S 2 wires.

DTC P0138: HO2S CIRCUIT-HIGH VOLTAGE-BANK 1, SENSOR 2 (5.7L "F" & "Y" BODIES)

Note. For circuit reference, see appropriate wiring diagram in WIRING DIAGRAMS article.

PCM supplies a bias voltage (about 450 mV) on HO2S 2 high and low signal circuits. Oxygen sensor voltage ranges from 10 mV when exhaust is lean to 1000 mV when exhaust is rich. PCM monitors and stores HO2S 2 voltage information. PCM then evaluates voltage samples to determine amount of time HO2S 2 voltage was out of range. PCM will compare stored HO2S 2 voltage samples taken each sample period and determine if majority of samples are fixed at greater than operating range. If PCM detects that voltage is greater than a predetermined voltage, DTC P0138 will set.

For duplication of DTC, ensure

DTCs P0101, P0102, P0103, P0112, P0113, P0117, P0118, P0121, P0122, P0123, P0125, P0200, P0335, P0336, P0351-P0358 or P1258 are not set.
Ignition voltage is greater than 9 volts.
Fuel system is operating in closed loop.
AIR, EGR and catalyst diagnostics are not active.
TP sensor angle is 2-70 percent.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-introduction__on-board-diagnostic-obd-system-check) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Start and warm engine to normal operating temperature. Increase engine speed to about 1200 RPM. Using scan tool, select ENGINE 1 DATA LIST and monitor HO2S 2 display. If voltage is greater than 930 mV, go to step 4 . If voltage is not greater than 930 mV, go to next step.
Turn ignition on, with engine off. Using scan tool, review FREEZE FRAME and/or FAILURE RECORDS data and note parameters. Turn ignition off for about 15 seconds. Start engine and operate vehicle within conditions required for this diagnostic to run, and as close to conditions recorded in FREEZE FRAME/FAILURE RECORDS as possible. Select DTC function, and then enter DTC P0138. If scan tool indicates that this test failed this ignition, go to next step. If scan tool does not indicate that this test failed this ignition, see «DIAGNOSTIC AIDS»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p0135-p0204) .
Turn ignition on, with engine off. Monitor HO2S 2 voltage with scan tool. If voltage is 350-550, go to next step. If voltage is not 350-550 mV, see «DIAGNOSTIC AIDS»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p0135-p0204) .
While monitoring HO2S 2 voltage, remove HO2S 2 heater fuse. If voltage drops to within a range of 350-550 mV with power to heater disconnected, go to next step. If voltage does not drop to within specified range, go to step 7 .
Reinstall fuse. Disconnect HO2S 2 harness connector. Using a jumper wire, jumper HO2S 2 low circuit to ground. Monitor HO2S 2 voltage with scan tool. If voltage is 350-550 mV, go to step 10 . If voltage is not 350-550 mV, go to step 8 .
Turn ignition off. Disconnect PCM harness connector C1. Disconnect HO2S 2 harness connector. Turn ignition on. Check for voltage between ground and HO2S 2 signal circuit at PCM harness connector. If voltage is present, go to next step. If no voltage is present, go to step 9 .
Repair short to voltage in HO2S 2 signal circuit. After repairs, go to step 11 .
Replace PCM. Program replacement PCM using required equipment. After repairs, go to step 11 .
Replace HO2S 2. After repairs, go to next step.
Using scan tool, clear DTCs. Start and warm engine to normal operating temperature. Select DTC, SPECIFIC, and then enter DTC P0138. Operate vehicle within conditions for setting this DTC. If scan tool indicates that this test ran and passed, go to next step. If scan tool does not indicate that this test ran and passed, go to step 2 .
Using scan tool, select CAPTURE INFO, REVIEW INFO function. If any undiagnosed DTCs are displayed, go to applicable DTC test. If no undiagnosed DTCs are displayed, system is okay.

Check for HO2S 2 wires grounding against exhaust manifold. Oxygen supply inside HO2S 2 is necessary for proper operation. This supply of oxygen is provided through HO2S 2 wires. Inspect all wires and terminals for breaks or contamination.

Check for rich fuel injector(s) or excessively high fuel pressure. Perform injector balance test. See appropriate SYSTEM & COMPONENT TESTING article. Check for saturated EVAP canister or incorrectly installed MAF sensor. Disconnect MAF sensor and observe if rich condition is corrected. Check for leaking fuel pressure regulator or leaking regulator vacuum hose. Check TP sensor. An intermittent TP sensor output will cause system to go rich.

DTC P0139: HO2S CIRCUIT-SLOW RESPONSE-BANK 1, SENSOR 2 (3.0L "V" BODY)

Note. For circuit reference, see appropriate wiring diagram in WIRING DIAGRAMS article.

If ECM detects that HO2S 2 voltage is.401-.519 volts for more than one minute, DTC P0139 will set. For duplication of DTC, ensure engine is running and battery voltage is greater than 11 volts.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-introduction__on-board-diagnostic-obd-system-check) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Ensure HO2S 2 is properly installed. Check for damaged HO2S 2 wiring or corroded terminal connections. Repair as necessary. After repairs, go to step 23 . If no problem is found, go to next step.
Turn ignition on, with engine off. Disconnect HO2S 2 harness connector. Measure voltage between ground and signal circuit at HO2S 2 harness connector. If voltage is about 900 mV, go to next step. If voltage is not about 900 mV, go to step 10 .
Measure voltage between ground and low circuit at HO2S 2 harness connector. If voltage is 700-800 mV, go to next step. If voltage is not 700-800 mV, go to step 6 .
Using a fused jumper wire, jumper HO2S 2 signal circuit to ground. Monitor HO2S 2 voltage with scan tool. If voltage is between -400 mV and -410 mV, go to step 20 . If voltage is not as specified, go to step 22 .
Continue monitoring HO2S 2 voltage while disconnecting each remaining oxygen sensor. If disconnecting one of the sensors restores voltage to 700-800 mV, go to step 13 . If voltage is not restored to 700-800 mV with all sensors disconnected, go to next step.
Leave all oxygen sensors disconnected. Turn ignition off. Disconnect ECM harness connectors. Turn ignition on. Check for voltage between battery ground and HO2S 2 low circuit at ECM harness connector. If any voltage is present, go to step 14 . If no voltage is present, go to next step.
Check HO2S 2 low circuit for continuity between HO2S 2 and ECM. If continuity is present, go to next step. If continuity is not present, go to step 15 .
Check HO2S 2 low circuit for continuity to battery ground. If continuity is present, go to step 16 . If continuity is not present, go to step 21 .
Leave HO2S 2 disconnected. Turn ignition off. Disconnect ECM harness connectors. Turn ignition on. Check for voltage between battery ground and HO2S 2 signal circuit at ECM harness connector. If any voltage is present, go to step 17 . If no voltage is present, go to next step.
Check HO2S 2 signal circuit for continuity between HO2S 2 and ECM. If continuity is present, go to next step. If continuity is not present, go to step 18 .
Check HO2S 2 signal circuit for continuity to battery ground. If continuity is present, go to step 19 . If continuity is not present, go to step 21 .
Replace shorted HO2S 2. After repairs, go to step 23 .
Repair short to voltage in HO2S 2 low circuit. After repairs, go to step 23 .
Repair open or high resistance in HO2S 2 low circuit. After repairs, go to step 23 .
Repair short to ground in HO2S 2 low circuit. After repairs, go to step 23 .
Repair short to voltage in HO2S 2 signal circuit. After repairs, go to step 23 .
Repair open or high resistance in HO2S 2 signal circuit. After repairs, go to step 23 .
Repair short to ground in HO2S 2 signal circuit. After repairs, go to step 23 .
Replace HO2S 2. After repairs, go to step 23 .
Check ECM for poor harness connections. Repair as necessary. After repairs, go to step 23 . If connections are okay, go to next step.
Replace ECM. Program replacement ECM using required equipment. Ensure ECM is programed with frequency code of theft deterrent module. After repairs, go to next step.
Using scan tool, clear DTCs. Start and warm engine to normal operating temperature. Select DTC, SPECIFIC, and then enter DTC P0139. Operate vehicle within conditions for setting this DTC. If scan tool indicates that this test ran and passed, go to next step. If scan tool does not indicate that this test ran and passed, go to step 2 .
Using scan tool, select CAPTURE INFO, REVIEW INFO function. If any undiagnosed DTCs are displayed, go to applicable DTC test. If no undiagnosed DTCs are displayed, system is okay.

HO2S 2 pigtail or harness may be mispositioned and contacting exhaust system. Inspect harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, poor terminal-to-wire connection, corrosion or water intrusion.

DTC P0140: HO2S CIRCUIT-INSUFFICIENT ACTIVITY-SENSOR 2 (1.9L SATURN)

Note. For circuit reference, see appropriate wiring diagram in WIRING DIAGRAMS article.

When Heated Oxygen Sensor 2 (HO2S 2) temperature reaches about 600°F (316°C), it becomes an electrical source that responds to the oxygen content in the exhaust. PCM produces a bias voltage of about 450 mV on the oxygen sensor circuit. When sensor is cold, its internal resistance is extremely high; therefore, the PCM recognizes the bias as an open circuit. As the sensor warms up, the internal resistance decreases. When sensor reaches about 600°F (316°C), it starts producing a voltage based on the oxygen content in the exhaust stream.

DTC P0140 will set if HO2S 2 voltage is 391-491 mV for 90 seconds when engine is at normal operating temperature, engine is running for more than one minute, and no other engine sensor or misfire DTCs have been set or commanded air/fuel ratio is about 14.7:1. HO2S 2 signal is continuously monitored once these conditions are met.

If DTC P0140 and P0141 are both set, diagnose DTCs first using DTC P0141 test. Operate engine for 3 minutes or greater. Connect scan tool. Ensure ECT is at greater than 140°F (60°C). Increase engine speed to 3000 RPM. Monitor HO2S 2 voltage. HO2S 2 voltage should vary greater than and less than 450 mV. If voltage is varies as specified, problem is intermittent. See «DIAGNOSTIC AIDS»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p0135-p0204) . If voltage does not vary as specified, go to next step.
Turn engine off. Turn ignition on. Disconnect HO2S 2 harness connector. Using a jumper wire, jumper HO2S 2 harness connector terminals "A" and "B" together. If scan tool reads less than 100 mV, check tightness of harness connector terminals. If scan tool reads 100 mV or greater, go to next step.
Remove jumper wire. Connect jumper wire between HO2S 2 harness connector terminal "B" and chassis ground. If scan tool reads less than 100 mV, check for open in ground circuit between sensor and chassis ground. If scan tool does not read less than 100 mV, go to next step.
Remove jumper wire. Measure voltage on HO2S 2 signal circuit at harness connector terminal "B". If voltage is 300-600 mV, replace PCM. If voltage is greater than 600 mV, check for open ground circuit, terminal tightness or faulty PCM. If voltage is less than 300 mV, check for open signal circuit, terminal tightness or faulty PCM.

If DTC P0141 is also present, diagnose this DTC first. An inoperative heater may cause the sensor to cool down, causing DTC to set. PCM will not perform a catalyst monitor test if DTC P0140 is present.

Use scan tool to review malfunction history diagnostic information. This data can be used to duplicate a problem. Check tightness of harness connector terminals. Normal scan tool readings in closed loop will show the oxygen sensor voltage varying between 100 mV and 999 mV. DTC can set or cause false oxygen sensor readings if the oxygen sensor ground is loose.

DTC P0140: HO2S CIRCUIT-INSUFFICIENT ACTIVITY-SENSOR 2 (2.2L "J" BODY, 2.2L "S" SERIES & 2.4L "J" & "N" BODIES)

Note. For circuit reference, see appropriate wiring diagram in WIRING DIAGRAMS article.

The Heated Oxygen Sensor 2 (HO2S 2), located at rear of catalytic converter, produces an output signal relative to oxygen storage capacity of catalytic converter. HO2S 2 signal is less active than signal produced by front oxygen sensor. DTC P0140 will set if HO2S 2 signal voltage remains at 425-460 mV for a predetermined amount of time.

For duplication of DTC, ensure

DTCs P0105, P0107, P0108, P0112, P0113, P0117, P0118, P0122, P0123, P0171, P0200, P0300, P0301, P0302, P0303, P0304, P0335, P0440, P0442, P0446, P0506, P0507, P0601, P0602 or P1441 are not set.
Airflow is greater than 5.5 gm/s.
ECT is greater than 104°F (40°C).
TP sensor angle is 4-56 percent.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-introduction__on-board-diagnostic-obd-system-check) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Ensure engine is at normal operating temperature. Start engine. Increase engine speed to 1200 RPM for 2 minutes. Observe HO2S 2 voltage. If voltage is 425-460 mV, go to step 4 . If voltage is not 425-460 mV, go to next step.
Turn ignition on, with engine off. Using scan tool, review FREEZE FRAME data and note parameters. Start engine and operate vehicle within conditions required for setting this DTC, and as close to conditions recorded in FREEZE FRAME as possible. Observe HO2S 2 voltage. If voltage is 425-460 mV, go to next step. If voltage is not 425-460 mV, go to step 11 .
Turn ignition on, with engine off. Disconnect HO2S 2 harness connector. Connect a jumper wire between ground and signal circuit and ground circuit terminals at HO2S 2 harness connector. If voltage is less than 100 mV, go to next step. If voltage is not less than 100 mV, go to step 6 .
Turn ignition off. Check for open or poor connection at HO2S 2 harness connector. Repair as necessary. After repairs, go to step 11 . If circuit is okay, go to step 7 .
Turn ignition off. Remove jumper wire. Using a test light connected to battery positive, probe ground circuit at HO2S 2 harness connector. If test light illuminates, go to step 8 . If test light does not illuminate, go to step 9 .
Replace HO2S 2. After repairs, go to step 11 .
Check HO2S 2 signal circuit for an open or poor connection. Repair as necessary. After repairs, go to step 11 . If circuit is okay, go to step 10 .
Repair open in HO2S 2 ground circuit. After repairs, go to step 11 .
Replace PCM. Program replacement PCM using required equipment. After repairs, go to next step.
Using scan tool, clear DTCs. Start engine and allow it to idle. Ensure engine is at normal operating temperature. Operate vehicle within conditions required for setting this DTC. Select SPECIFIC DTC function, and then enter DTC P0140. If scan tool indicates this test ran and passed, go to next step. If scan tool does not indicate this test ran and passed, go to step 2 .
If any other DTCs are set, diagnose DTCs as necessary. If no other DTCs are set, system is okay.

Check oxygen sensor pigtail wire for breaks and contamination. An intermittent problem can be caused by misrouted harness, rubbed-through wire insulation or broken wire inside insulation. Check for intermittent open in HO2S 2 signal circuit wire. DO NOT attempt to repair damaged oxygen sensor connector or wiring. If damage is detected, replace oxygen sensor.

DTC P0140: HO2S CIRCUIT-INSUFFICIENT ACTIVITY-BANK 1, SENSOR 2 (3.0L "V" BODY)

Note. For circuit reference, see appropriate wiring diagram in WIRING DIAGRAMS article.

For duplication of DTC, ensure engine is running and battery voltage is greater than 11 volts.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-introduction__on-board-diagnostic-obd-system-check) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Inspect for corrosion on HO2S terminals. Ensure HO2S is securely installed. Check terminal tension and for damaged wiring. Repair as necessary. After repairs, go to step 23 . If no problem is found, go to next step.
Turn ignition on, with engine off. Disconnect HO2S 2 harness connector. Using DVOM, measure voltage between ground and signal circuit at HO2S 2 harness connector. If voltage is about 900 mV, go to next step. If voltage is not about 900 mV, go to step 10 .
Using DVOM, measure voltage between ground and low circuit at HO2S 2 harness connector. If voltage is 700-800 mV, go to next step. If voltage is not 700-800 mV, go to step 6 .
Using a fused jumper wire, jumper HO2S 2 harness connector signal circuit to ground. Using scan tool, monitor HO2S 2 voltage. If HO2S 2 voltage on scan tool is -400 mV to -410 mV, go to step 20 . If HO2S 2 voltage value on scan tool is not -400 mV to -410 mV, go to step 22 .
Continue to monitor voltage from HO2S 2 low circuit between harness connector and ground. Disconnect the 3 other HO2S. As each sensor is disconnected, recheck voltage. If disconnecting the other sensors restores voltage to 700-800 mV, go to step 13 . If disconnecting the other sensors does not restore voltage to 700-800 mV, go to next step.
Leave all HO2S disconnected. Turn ignition off. Disconnect ECM harness connector located in engine compartment relay center. Turn ignition on. Using DVOM, check voltage between ground and HO2S 2 low circuit at ECM harness connector. If voltage is present, go to step 14 . If no voltage is present, go to next step.
Using DVOM, check harness continuity of HO2S 2 low circuit. If continuity is present, go to next step. If continuity is not present, go to step 15 .
Using DVOM, check harness continuity between HO2S 2 low circuit and ground. If continuity is present, go to step 16 . If continuity is not present, go to step 21 .
Leave all HO2S disconnected. Turn ignition off. Disconnect ECM harness connector located in engine compartment relay center. Turn ignition on. Using DVOM, check voltage between ground and HO2S 2 signal circuit at ECM harness connector. If any voltage is present, go to step 17 . If no voltage is present, go to next step.
Using DVOM, check harness continuity of HO2S 2 signal circuit. If continuity is present, go to next step. If continuity is not present, go to step 18 .
Using DVOM, check harness continuity between HO2S 2 signal circuit and ground. If continuity is present, go to step 19 . If continuity is not present, go to step 21 .
Replace shorted HO2S 2. After repairs, go to step 23 .
Repair short to voltage in HO2S 2 low circuit. After repairs, go to step 23 .
Repair open or high resistance in HO2S 2 low circuit. After repairs, go to step 23 .
Repair short to ground in HO2S 2 low circuit. After repairs, go to step 23 .
Repair short to voltage in HO2S 2 signal circuit. After repairs, go to step 23 .
Repair open or high resistance in HO2S 2 signal circuit. After repairs, go to step 23 .
Repair short to ground in HO2S 2 signal circuit. After repairs, go to step 23 .
Replace HO2S 2. After repairs, go to step 23 .
Check for poor connections and terminal tension at ECM harness connector. Repair as necessary. After repairs, go to step 23 . If connections and terminals are okay, go to next step.
Replace ECM. New ECM must be programmed with theft deterrent module frequency code currently on vehicle. After repairs, go to next step.
Using scan tool, clear DTCs. Start engine and allow it to idle. Ensure engine is at normal operating temperature. Operate vehicle within conditions required for setting this DTC. Select SPECIFIC DTC function, and then enter DTC P0140. If scan tool indicates this test ran and passed, go to next step. If scan tool does not indicate this test ran and passed, go to step 2 .
If other DTCs were present during OBD system check and have not been diagnosed, go to applicable DTC. If no other DTCs are present, system is okay.

An exhaust leak may cause outside air to be pulled into exhaust gas stream past HO2S2 , causing this DTC to set. Check for exhaust leaks near HO2S 2.

DTC P0140: HO2S CIRCUIT-INSUFFICIENT ACTIVITY-SENSOR 2 (3.1L "N" & "W" BODIES & 3.4L "N" BODY & "U" SERIES)

Note. For circuit reference, see appropriate wiring diagram in WIRING DIAGRAMS article.

Three-Way Catalyst (TWC) system is used to control emissions. PCM uses signal from Heated Oxygen Sensor 2 (HO2S 2) behind TWC to read efficiency of TWC. PCM will set DTC P0140 if TWC oxygen storage capacity is less than a predetermined threshold.

For duplication of DTC, ensure no active misfire, fuel injector circuit, fuel trim, EGR, EVAP system, TP, IAT, MAP, ECT, MAF or CKP sensor DTCs are set, engine is running, and engine coolant temperature is greater than 149°F (65°C).

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-introduction__on-board-diagnostic-obd-system-check) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Start engine and allow it to reach operating temperature. Place gear selector in Park or Neutral, and apply parking brake. Increase engine speed to greater than 1200 RPM for 2 minutes. Using scan tool, read HO2S 2 voltage. If voltage is varying outside of 400-500 mV range, go to next step. If voltage is varying as specified, go to step 4 .
Turn engine off. Turn ignition on, with engine off. Using scan tool, read and record FAILURE RECORDS data. Operate vehicle within conditions noted in FAILURE RECORDS data. Using scan tool, read SPECIFIC DTC. If scan tool displays DTC P0140 FAILED THIS IGN, go to next step. If scan tool does not display DTC P0140 FAILED THIS IGN, see «DIAGNOSTIC AIDS»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p0135-p0204) .
Disconnect HO2S 2 harness connector. Connect a jumper wire between ground and HO2S 2 harness connector signal and low circuits. If voltage is less than 150 mV, go to step 8 . If voltage is not less than 150 mV, go to next step.
Remove jumper wire. Using DVOM, measure voltage between HO2S 2 harness connector signal and heater ground circuits. If voltage is about 950 mV on 3.1L, or 450 mV on 3.4L, go to next step. If voltage is not as specified, go to step 7 .
Turn ignition off. Disconnect PCM harness connectors. Measure resistance of HO2S 2 harness connector ground circuit. If resistance is greater than 5 ohms, repair open or faulty connection. After repairs, go to step 13 . If resistance is not greater than 5 ohms, go to step 9 .
Turn ignition off. Disconnect PCM harness connectors. Measure resistance of HO2S 2 harness connector signal circuit. If resistance is greater than 5 ohms, repair open or faulty connection. After repairs, go to step 13 . If resistance is not greater than 5 ohms, go to step 10 .
Check for faulty connection at HO2S 2. Repair as necessary. After repairs, go to step 13 . If connection is okay, go to step 11 .
Check HO2S 2 ground circuit for faulty connection at PCM. Repair as necessary. After repairs, go to step 13 . If connection is okay, go to step 12 .
Check HO2S 2 signal circuit for faulty connection at PCM. Repair as necessary. After repairs, go to step 13 . If connection is okay, go to step 12 .
Replace HO2S 2. After repairs, go to step 13 .
Replace PCM. Program replacement PCM using required equipment. After repairs, go to next step.
Using scan tool, read and record FAILURE RECORDS data, and clear DTCs. Operate vehicle within conditions noted in FAILURE RECORDS data. Using scan tool, select SPECIFIC DTC INFO for DTC P0140. If scan tool displays DTC P0140 FAILED THIS IGN, go to step 2 . If scan tool does not display DTC P0140 FAILED THIS IGN, system is okay.

Check for faulty connections or damaged harness. If connections and harness appear okay, observe HO2S 2 display on scan tool while moving all related harness and connectors. A change in scan tool display indicates fault location. Check HO2S 2 heater operation.

DTC P0140: HO2S CIRCUIT-INSUFFICIENT ACTIVITY-SENSOR 2 (3.5L "W" BODY)

Note. For circuit reference, see appropriate wiring diagram in WIRING DIAGRAMS article.

Powertrain Control Module (PCM) supplies about 450 mV to Heated Oxygen Sensor 2 (HO2S 2). The HO2S 2 supplies a varying voltage from about 800 mV when exhaust is rich to about 50 mV when exhaust is lean. PCM monitors and stores sensor voltage information and evaluates the voltage samples to determine amount of time sensor voltage is out of range. If PCM detects that HO2S 2 voltage remains at or near 450 mV for an extended period, DTC P0140 will set.

For duplication of DTC, ensure engine is running, and no active fuel trim, fuel injector circuit, misfire, EVAP system, EGR system, TP, IAT, MAP, ECT, CKP, or MAF sensor DTCs are present.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-introduction__on-board-diagnostic-obd-system-check) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Using scan tool, clear DTCs. Reset fuel trim values. Start engine and allow it to reach normal operating temperature. Monitor HO2S 2 voltage on scan tool. If voltage is fixed at 351-551 mV, go to step 4 . If voltage is not as specified, go to next step.
DTC is intermittent. Faulty wiring and harness connections or exhaust leaks may have set this DTC. Repair as necessary. After repairs, go to step 17 . If no problem is found, see «DIAGNOSTIC AIDS»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p0135-p0204) .
Turn ignition off. Disconnect HO2S 2 harness connector. Using jumper wires, jumper HO2S 2 high and low signal circuits to ground. Turn ignition on, with engine off. Monitor HO2S 2 voltage with scan tool. If voltage is less than 20 mV, go to step 7 . If voltage is not less than 20 mV, go to next step.
Turn ignition off. Remove jumper wires. Disconnect PCM harness connector containing HO2S 2 circuits. Measure resistance of HO2S 2 high and low signal circuits. If each circuit resistance is less than 5 ohms, go to next step. If either circuit resistance is not less than 5 ohms, go to step 9 .
Check for faulty PCM harness connections. Repair as necessary. After repairs, go to step 17 . If connections are okay, go to step 16 .
Remove jumper wires. Turn ignition on, with engine off. Connect a test light between heater ignition feed and heater ground circuits at HO2S 2 harness connector. If test light illuminates, go to next step. If test light does not illuminate, go to step 10 .
Turn ignition off. Reconnect HO2S 2 harness connector. Disconnect PCM harness connector containing HO2S 2 circuits. Measure resistance between HO2S 2 low signal circuit and any PCM ground circuit at PCM harness connector. If resistance is less than 500 ohms, go to step 12 . If resistance is not less than 500 ohms, go to step 11 .
Repair circuit with high resistance. After repairs, go to step 17 .
Repair HO2S 2 heater ignition feed or ground circuit. After repairs, go to step 17 .
Repair high resistance between HO2S 2 low circuit and PCM ground circuit. After repairs, go to step 17 .
Check for an exhaust leak upstream of HO2S 2. Repair as necessary. After repairs, go to step 17 . If no leaks are found, go to next step.
Allow engine to completely cool. Measure resistance between HO2S 2 low signal circuit and any PCM ground circuit at PCM harness connector. If resistance is less than 500 ohms, go to step 15 . If resistance is not less than 500 ohms, go to next step.
Remove HO2S 2. Clean threads and apply anti-seize compound, and then reinstall. Measure resistance between HO2S 2 low signal circuit and any PCM ground circuit at PCM harness connector. If resistance is less than 500 ohms, go to step 17 . If resistance is not less than 500 ohms, go to next step.
Replace HO2S 2. After repairs, go to step 17 .
Replace PCM. Program replacement PCM using required equipment. After repairs, go to next step.
Using scan tool, clear DTCs. Turn ignition off and wait 15 seconds. Start engine and operate vehicle under conditions required to set this DTC. If scan tool indicates this test ran and passed, go to next step. If scan tool does not indicate this test ran and passed, go to step 2 .
Using scan tool, select CAPTURE INFO, REVIEW INFO function. If any undiagnosed DTCs are displayed, go to applicable DTC test. If no undiagnosed DTCs are displayed, system is okay.

Check for poor connection at PCM. Check for damaged wiring harness. An intermittent problem can be caused by a poor connection, rubbed-through wire insulation or broken wire inside insulation.

Turn ignition on, with engine off. Using scan tool, monitor HO2S 2 voltage. Voltage should gradually drop to less than 250 mV or rise to greater than 600 mV. If voltage is not as specified, disconnect HO2S 2 connector. Connect a test light between ignition feed circuit and heater ground circuit terminals at HO2S 2 harness connector. If test light does not illuminate, repair open ignition feed circuit. If test light illuminates, replace HO2S 2.

HO2S 2 requires an outside source of air for proper operation. Air is supplied through HO2S 2 wiring. Check wires and connections for breaks or contamination. DO NOT solder HO2S 2 wiring. Solder will obstruct air path.

DTC P0140: HO2S CIRCUIT-INSUFFICIENT ACTIVITY-SENSOR 2 (3.8L "C", "F", "G", "H" & "W" BODIES)

Note. For circuit reference, see appropriate wiring diagram in WIRING DIAGRAMS article.

PCM provides about 0.45 volt reference to HO2S 2. HO2S 2 sensor signal voltage varies from about one volt when exhaust is rich to about 0.1 volt when exhaust is lean. PCM reads and stores sensor voltage information and evaluates the voltage samples to determine amount of time sensor voltage is out of range. If HO2S 2 voltage is out of predetermined range, DTC P0140 will set.

For duplication of DTC, ensure engine is running and no active fuel trim, fuel injector circuit, misfire, EVAP system, EGR pintle position, TP, IAT, MAP, ECT, CKP, or MAF sensor DTCs are set.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-introduction__on-board-diagnostic-obd-system-check) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Start and warm engine to normal operating temperature. Place transmission in Park or Neutral. Apply parking brake. Increase engine speed to greater than 1200 RPM for 2 minutes. Using scan tool, monitor HO2S 2 voltage. If displayed voltage is not switching from greater than 475 mV to less than 425 mV, go to next step. If voltage is switching as specified, go to step 4 .
Turn engine off. Turn ignition on, engine off. Using scan tool, read and record FAILURE RECORDS data. Operate vehicle within conditions noted in FAILURE RECORDS data. Using scan tool, read SPECIFIC DTC. If scan tool displays DTC P0140 FAILED THIS IGN, go to next step. If scan tool does not display DTC P0140 FAILED THIS IGN, see «DIAGNOSTIC AIDS»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p0135-p0204) .
Disconnect HO2S 2 harness connector. Connect a jumper wire between HO2S 2 harness connector signal and ground circuits, and chassis ground. If voltage is less than 150 mV, go to step 8 . If voltage is not less than 150 mV, go to next step.
Remove jumper wire. Using DVOM, measure voltage between HO2S 2 harness connector signal and heater ground circuits. If voltage is about 450 mV, go to next step. If voltage is not about 450 mV, go to step 7 .
Turn ignition off. Disconnect PCM harness connectors. Measure resistance of HO2S 2 harness connector ground circuit. If resistance is greater than 5 ohms, repair open or faulty connection. After repairs, go to step 13 . If resistance is not greater than 5 ohms, go to step 9 .
Turn ignition off. Disconnect PCM harness connectors. Measure resistance of HO2S 2 harness connector signal circuit. If resistance is greater than 5 ohms, repair open or faulty connection as necessary. After repairs, go to step 13 . If resistance is not greater than 5 ohms, go to step 10 .
Check for faulty connection at HO2S 2. Repair as necessary. After repairs, go to step 13 . If connection is okay, go to step 11 .
Check HO2S 2 ground circuit for faulty connection at PCM. Repair as necessary. After repairs, go to step 13 . If connection is okay, go to step 12 .
Check HO2S 2 signal circuit for faulty connection at PCM. Repair as necessary. After repairs, go to step 13 . If connection is okay, go to step 12 .
Replace HO2S 2. After repairs, go to step 13 .
Replace PCM. Program replacement PCM using required equipment. After repairs, go to next step.
Using scan tool, read and record FAILURE RECORDS data, and clear DTCs. Operate vehicle within conditions noted in FAILURE RECORDS data. Using scan tool, select SPECIFIC DTC INFO for DTC P0140. If scan tool displays DTC P0140 FAILED THIS IGN, go to step 2 . If scan tool does not display DTC P0140 FAILED THIS IGN, system is okay.

DTC P0140: HO2S CIRCUIT-INSUFFICIENT ACTIVITY-BANK 1, SENSOR 2 (4.3L, 5.0L, 5.7L & 7.4L "C", "G", "K" & "P" SERIES)

Note. For circuit reference, see appropriate wiring diagram in WIRING DIAGRAMS article.

HO2S 2 heater provides for faster sensor warm-up allowing sensor to become active in a shorter period of time and remain active during long extended idle. DTC determines if HO2S 2 or HO2S 2 circuit is open. DTC P0140 will set if VCM fails to detect minimum number of HO2S 2 voltage transitions greater than and less than bias voltage range of 300-600 mV.

For duplication of DTC, ensure

DTC P0140 is not set.
No active EVAP system, misfire, TP, IAT, MAP, ECT or MAF sensor DTCs are set.
No intrusive tests are in progress.
No device controls are active.
System voltage is 11.7-18 volts.
Engine run time is greater than 2 minutes.
Decel fuel cut-off mode is not active.
ECT is 137°F (58.5°C) or greater.
MAF is 13 grams per second.
System is in closed loop.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-introduction__on-board-diagnostic-obd-system-check) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Using scan tool, store DTC information from VCM. Clear DTCs and reset fuel trim values. Start engine and allow it to reach normal operating temperature. Monitor HO2S 2 voltage on scan tool. If voltage is fixed at 400-473 mV, go to step 4 . If voltage is not as specified, go to next step.
Condition that set DTC is not present at this time. If any additional DTCs are set, go to applicable DTC test. If no additional DTCs are set, see «DIAGNOSTIC AIDS»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p0135-p0204) .
Turn ignition off. Disconnect HO2S 2 harness connector. Using jumper wires, jumper HO2S 2 high and low signal circuits to ground. Turn ignition on. Monitor HO2S 2 voltage with scan tool. If voltage is less than 20 mV, go to step 7 . If voltage is not less than 20 mV, go to next step.
Turn ignition off. Remove jumper wires. Disconnect VCM harness connector containing HO2S 2 circuits. Measure resistance of HO2S 2 high and low signal circuits between HO2S 2 and VCM. If resistance of both circuits is less than 5 ohms, go to next step. If resistance of either circuit is not less than 5 ohms, go to step 9 .
Check VCM harness connections. Repair as necessary. After repairs, go to step 17 . If connections are okay, go to step 16 .
Remove jumper wires from HO2S 2. Turn ignition on. Connect test light between HO2S 2 heater ignition feed and ground circuits at HO2S 2 harness connector. If test light illuminates, go to next step. If test light does not illuminate, go to step 10 .
Turn ignition off. Reconnect HO2S 2 harness connector. Disconnect VCM harness connector containing HO2S 2 low signal circuit and VCM harness connector containing VCM ground circuits. Measure resistance between HO2S 2 low signal circuit and one of the VCM ground circuit terminals at VCM harness connector. If resistance is less than 500 ohms, go to step 12 . If resistance is not less than 500 ohms, go to step 11 .
Repair circuit with high resistance. After repairs, go to step 17 .
Repair HO2S 2 heater ignition feed or ground circuit. After repairs, go to step 17 .
Repair high resistance between HO2S 2 low signal circuit and VCM ground circuit. After repairs, go to step 17 .
Check for exhaust leaks upstream of HO2S 2. Repair as necessary. After repairs, go to step 17 . If no leaks are found, go to next step.
Allow engine to completely cool. Measure resistance between HO2S 2 low signal circuit and one of the VCM ground circuit terminals at VCM harness connector. If resistance is less than 500 ohms, go to step 15 . If resistance is not less than 500 ohms, go to next step.
Remove HO2S 2. Clean threads and apply anti-seize compound, and then reinstall. Measure resistance between HO2S 2 low signal circuit and one of the VCM ground circuit terminals at VCM harness connector. If resistance is less than 500 ohms, go to step 17 . If resistance is not less than 500 ohms, go to next step.
Replace HO2S 2. After repairs, go to step 17 .
Replace VCM. Program replacement VCM using required equipment. Perform Passlock® reprogramming and CKP system variation learn procedures. After repairs, go to next step.
Using scan tool, clear DTCs. Start engine and operate vehicle under conditions required to set this DTC. If scan tool indicates this test ran and passed, go to next step. If scan tool does not indicate this test ran and passed, go to step 2 .
Using scan tool, select CAPTURE INFO, REVIEW INFO function. If any undiagnosed DTCs are displayed, go to applicable DTC test. If no undiagnosed DTCs are displayed, system is okay.

An intermittent may be caused by a poor connection, rubbed-through wire insulation or a broken wire inside insulation. Inspect harness connectors for backed-out terminals, improper mating, broken locks, improperly formed or damaged terminals, poor terminal-to-wire connection, and damaged harness.

With ignition on and engine off, HO2S 2 voltage on scan tool should gradually decrease to less than.15 volt indicating heater is operating properly. If voltage does not decrease as specified, disconnect HO2S 2 connector and connect a test light between HO2S 2 connector terminals "C" and "D" (engine harness side). If test light illuminates, replace HO2S 2. If test light does not illuminate, repair open in HO2S 2 heater ground circuit or HO2S 2 ignition feed circuit.

Using scan tool, monitor signal voltage while wiggling HO2S 2 related connectors and wiring harness with a warm engine running at part throttle in closed loop. If a failure is induced, signal voltage will change from normal fluctuating voltage of greater than.6 volt and less than.3 volt, to a fixed voltage of about.45 volt. A change in voltage will assist in isolating location of fault. DO NOT solder HO2S wires.

DTC P0140: HO2S CIRCUIT-INSUFFICIENT ACTIVITY-BANK 1, SENSOR 2 (4.8L, 5.3L & 6.0L "C" & "K" SERIES & 5.7L "F" & "Y" BODIES)

Note. For circuit reference, see appropriate wiring diagram in WIRING DIAGRAMS article.

Powertrain Control Module (PCM) supplies about.45 volt to Heated Oxygen Sensor 2 (HO2S 2). The HO2S 2 generates a voltage that varies from about one volt when exhaust is rich to about.10 volt when exhaust is lean. PCM monitors and stores sensor voltage information and evaluates the voltage samples to determine amount of time sensor voltage is out of range. If PCM detects HO2S 2 voltage remains at or near.45 volt for an extended period of time, DTC P0140 will set.

For duplication of DTC, ensure

DTCs P0101, P0102, P0103, P0112, P0113, P0117, P0118, P0121, P0122, P0123, P0125, P0200, P0335, P0336, P0351-P0358 and P1258 are not set.
Ignition voltage is greater than 9 volts.
AIR, EGR and catalyst diagnostics are not active.
Fuel system is operating in closed loop.
Engine run time is greater than 70 seconds.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-introduction__on-board-diagnostic-obd-system-check) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Start and warm engine to normal operating temperature. Increase engine speed to 1200 RPM for 2 minutes. Using scan tool, select ENGINE 1 and note HO2S 2 voltage. If voltage varies from less than 350 mV to greater than 550 mV, go to next step. If voltage does not vary as specified, go to step 4 .
Turn ignition on. Using scan tool, read and record FAILURE RECORDS data. Turn ignition off for 15 seconds. Start engine and operate vehicle within conditions noted in FAILURE RECORDS data. Using scan tool, read SPECIFIC DTC. If scan tool displays DTC P0140 FAILED THIS IGN, go to next step. If scan tool does not display DTC P0134 FAILED THIS IGN, see «DIAGNOSTIC AIDS»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p0135-p0204) .
Turn ignition on, with engine off. Disconnect HO2S 2. Using jumper wires, jumper HO2S 2 high and low signal circuits to ground. Monitor HO2S 2 voltage with scan tool. If voltage is less than 200 mV, go to step 8 . If voltage is not less than 200 mV, go to next step.
Remove jumper wire from HO2S 2 low signal circuit. Measure voltage between ground and low signal circuit at HO2S 2 harness connector. If voltage is about 5 volts, go to next step. If voltage is not about 5 volts, go to step 7 .
Turn ignition off. Disconnect PCM harness connector C1. Check for continuity in HO2S 2 high signal circuit between HO2S 2 and PCM harness connectors. Repair open circuit if continuity is not present. After repairs, go to step 12 . If circuit is okay, go to step 10 .
Turn ignition off. Disconnect PCM harness connector C1. Check for continuity in HO2S 2 low signal circuit between HO2S 2 and PCM harness connectors. Repair open circuit if continuity is not present. After repairs, go to step 12 . If circuit is okay, go to step 10 .
Check HO2S 2 circuits for poor connections at HO2S 2 harness connector. Repair as necessary. After repairs, go to step 12 . If connections are okay, go to next step.
Replace HO2S 2. After repairs, go to step 12 .
Check HO2S 2 circuits for poor connections at PCM. Repair as necessary. After repairs, go to step 12 . If connections are okay, go to next step.
Replace PCM. Program replacement PCM using required equipment. After repairs, go to next step.
Using scan tool, clear DTCs. Start engine and operate vehicle under conditions required to set this DTC. If scan tool indicates this test ran and passed, go to next step. If scan tool does not indicate this test ran and passed, go to step 2 .
Using scan tool, select CAPTURE INFO, REVIEW INFO function. If any undiagnosed DTCs are displayed, go to applicable DTC test. If no undiagnosed DTCs are displayed, system is okay.

DTC P0141: HO2S HEATER CIRCUIT-SENSOR 2 (1.9L SATURN)

Note. For circuit reference, see appropriate wiring diagram in WIRING DIAGRAMS article.

HO2S 2 is mounted behind the catalytic converter. This sensor is used to determine the oxygen storage capability of the catalytic converter. Oxygen storage capability is used as a measurement of converter condition and its ability to perform its function. Sensor heater is controlled by PCM.

PCM diagnoses the heater and its related circuit by monitoring the electrical current. DTC P0141 will set if the current range does not fall within the calibrated limits. DTC will also set if current feedback is less than 0.5 amp or greater than 2.4 amps for longer than 50 seconds when catalyst temperature is less than 1427°F (775°C).

Note. If DTC P0405 (EGR) and P0443 (EVAP CCP) are present, replace faulty EGR fuse located in underhood fuse block.

Install scan tool. Start engine. Using scan tool, command O2S heater on while observing rear O2S current. If rear O2S reading is 0.5-2.4 amps, problem is intermittent. See «DIAGNOSTIC AIDS»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p0135-p0204) . If rear O2S reading is not 0.5-2.4 amps, go to next step.
If reading is greater than 2.4 amps, go to next step. If reading is less than 0.5 amp, go to step 5 .
Disconnect H02S 2 harness connector. If reading is now is zero amps, replace HO2S 2. If reading is not zero amps, go to next step.
Disconnect PCM harness connector J3. If reading now is zero amps, repair short to battery voltage in circuit between HO2S 2 terminal "B" and PCM. If reading is not zero amps, check circuit between ground and PCM and ground circuit between PCM and ignition switch. Repair as necessary. If circuits are okay, replace PCM.
Disconnect HO2S 2 harness connector. Using a fused jumper wire, jumper HO2S 2 harness connector terminals "B" and "D". If reading now is greater than 0.5 amp, repair poor connection to HO2S 2. If connection is okay, replace HO2S 2. If reading is not greater than 0.5 amp, go to next step.
Check voltage at HO2S 2 harness connector terminal "D". If battery voltage is not present, repair open in circuit. If battery voltage is present, check for short to ground or poor connection between HO2S 2 harness connector terminal "B" and PCM. Repair as necessary. If circuit is okay, replace PCM.

Use scan tool to review malfunction history diagnostic information. Data can be used to duplicate a problem. Check for proper terminal connections. Normal scan tool readings in "closed loop" will show oxygen sensor voltage varying between 10 mV and 999 mV.

DTC P0141: HO2S HEATER CIRCUIT-SENSOR 2 (2.2L "J" BODY, 2.2L "S" SERIES & 2.4L "J" & "N" BODIES)

Note. For circuit reference, see appropriate wiring diagram in WIRING DIAGRAMS article.

The Heated Oxygen Sensor 2 (HO2S 2), located at rear of catalytic converter, produces an output signal relative to oxygen storage capacity of catalytic converter. HO2S 2 signal is less active than signal produced by front Oxygen Sensor 1 (O2S 1). DTC P0141 will set if HO2S 2 voltage increase is less than 150 mV in 100-190 seconds.

For duplication of DTC, ensure ECT and IAT is less than 113°F (45°C), difference between ECT and IAT is less than 45°F (7°C), and TP angle is less than 18 percent.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-introduction__on-board-diagnostic-obd-system-check) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Turn ignition on, with engine off. Using scan tool, observe HO2S 2 voltage reading. If voltage gradually changes toward zero or one volt, go to step 13 . If voltage does not gradually change toward zero or one volt, go to next step.
Disconnect HO2S 2 harness connector. Connect a test light between ground and ignition feed circuit terminal at HO2S 2 harness connector. If test light illuminates, go to next step. If test light does not illuminate, go to step 5 .
Connect a test light between ground circuit and ignition feed circuit terminals at HO2S 2 harness connector. If test light illuminates, go to step 6 . If test light does not illuminate, go to step 7 .
Remove and inspect fuse for HO2S 2 ignition feed circuit. If fuse is open, go to step 8 . If fuse is okay, go to step 9 .
Turn ignition off. Inspect HO2S 2 harness connector for faulty terminals or poor connection. Repair as necessary. After repairs, go to step 13 . If connector is okay, go to step 10 .
Turn ignition off. Inspect HO2S 2 harness connector for faulty terminals or poor connection. Repair as necessary. After repairs, go to step 13 . If connector is okay, go to step 11 .
Check for short to ground in HO2S 2 ignition feed circuit. Repair as necessary. After repairs, replace fuse and go to step 13 .
Turn ignition off. Inspect HO2S 2 harness connector for faulty terminals or poor connection. Repair as necessary. After repairs, go to step 13 .
Replace HO2S 2. After repairs, go to step 13 .
Repair open in ground circuit. After repairs, go to step 13 .
Repair open in ignition feed circuit. After repairs, go to next step.
Using scan tool, clear DTCs. Start engine and allow it to idle. Ensure engine is at normal operating temperature. Operate vehicle within conditions required for setting this DTC. Select SPECIFIC DTC function, and then enter DTC P0141. If scan tool indicates this test ran and passed, go to next step. If scan tool does not indicate this test ran and passed, go to step 2 .
If any other DTCs are set, diagnose DTCs as necessary. If no other DTCs are set, system is okay.

Check oxygen sensor pigtail wire for breaks and contamination. An intermittent problem can be caused by misrouted harness, rubbed through wire insulation or broken wire inside insulation. DO NOT attempt to repair damaged oxygen sensor connector or wiring. If damage is detected, replace oxygen sensor.

DTC P0141: HO2S HEATER CIRCUIT-BANK 1, SENSOR 2 (3.0L "V" BODY)

Note. For circuit reference, see appropriate wiring diagram in WIRING DIAGRAMS article.

Using Heated Oxygen Sensors (HO2S) for fuel control decreases amount of time required to enter closed loop operation. Heated oxygen sensors when used post-catalyst, ensure sufficient heat is maintained for accurate catalyst monitoring.

When HO2S 2 is cold, signal voltage at ECM is about 450 mV. When ignition is turned on, switched battery voltage is supplied to HO2S 2 heaters via main relay. ECM controls heater operation by first modulating ground circuit when sensors are cold, and then turning them on continuously after predetermined amount of time. This prevents possibility of thermal shock to sensors by controlling sensor's rate of heating. As heater reaches operating temperature, HO2S 2 voltage responds by changing from bias voltage range to normal operation.

On cold start, ECM will track how much time it takes for HO2S 2 voltage to go above or below bias voltage range. If ECM determines that it took too much time for HO2S 2 to enter into normal operating range, this DTC P0141 will set. The time it takes HO2S 2 to reach operating temperature is based on amount of airflow into engine and start-up coolant temperature.

For duplication of DTC, ensure battery voltage is greater than 11 volts, and no HO2S 2 DTCs are present.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-introduction__on-board-diagnostic-obd-system-check) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Disconnect HO2S 2 harness connector. Using test light connected to ground, probe HO2S 2 harness connector switched battery feed circuit. If test light illuminates, go to next step. If test light does not illuminate, go to step 4 .
Start engine. Using test light connected to battery positive, probe HO2S 2 harness connector heater control circuit. If test light illuminates, go to step 9 . If test light does not illuminate, go to step 8 .
Check HO2S heater fuse. If fuse is okay, go to next step. If fuse is blown, go to step 6 .
Using test light connected to ground, check for power at HO2S 2 fuse. If test light illuminates, go to step 11 . If test light does not illuminate, go to step 12 .
Disconnect other front HO2S 2 connector. Using test light connected to battery positive, probe HO2S 2 harness connector switched battery feed circuit. If test light illuminates, go to step 13 . If test light does not illuminate, go to next step.
Using DVOM, measure resistance of both front HO2S 2 heaters at sensor pigtails. If resistance of both heaters is greater than 4 ohms, see «DIAGNOSTIC AIDS»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p0135-p0204) . If resistance of both heaters is not greater than 4 ohms, go to step 14 .
Turn ignition off. Disconnect ECM harness connector located in engine compartment relay center. Using DVOM, check continuity of heater control circuit between HO2S 2 and ECM harness connectors. If continuity is present, go to step 16 . If continuity is not present, go to step 15 .
Check for poor connections and terminal tension at HO2S 2 harness connector. Repair as necessary. After repairs, go to step 18 . If connections and terminals are okay, go to next step.
Replace HO2S 2. After repairs, go to step 18 .
Repair open or high resistance in switched battery feed circuit between fuse and HO2S 2. After repairs, go to step 18 .
Repair feed circuit to fuse. After repairs, go to step 18 .
Repair short to ground in switched battery feed circuit. After repairs, go to step 18 .
Replace HO2S 2 with low resistance heater. After repairs, go to step 18 .
Repair open or high resistance in heater control circuit. After repairs, go to step 18 .
Check for poor connections and terminal tension at ECM harness connector. Repair as necessary. After repairs, go to step 18 . If connections and terminals are okay, go to next step.
Replace ECM. New ECM must be programmed with theft deterrent module frequency code currently on vehicle. After repairs, go to next step.
Using scan tool, clear DTCs. Start engine and allow it to idle. Ensure engine is at normal operating temperature. Operate vehicle within conditions required for setting this DTC. Select SPECIFIC DTC function, and then enter DTC P0141. If scan tool indicates this test ran and passed, go to next step. If scan tool does not indicate this test ran and passed, go to step 2 .
If other DTCs were present during OBD system check and have not been diagnosed, go to applicable DTC. If no other DTCs are present, system is okay.

DTC P0141: HO2S HEATER CIRCUIT-SENSOR 2 (3.1L "N" & "W" BODIES & 3.4L "N" BODY & "U" SERIES)

Note. For circuit reference, see appropriate wiring diagram in WIRING DIAGRAMS article.

When ignition is turned on, battery voltage is supplied to HO2S 2 heater to provide for faster sensor warm-up, thus allowing sensor to become active in a shorter period of time. PCM reads amount of time necessary for sensor to become active after start-up. DTC P0141 will set if PCM determines that too much time was required for HO2S 2 to become active.

For duplication of DTC, ensure

No active misfire, fuel injector circuit, EVAP, EGR, fuel trim, TP, IAT, MAP, ECT, MAF or CKP DTCs are set.
ECT and IAT are less than 95°F (35°C) at start-up.
Difference between ECT and IAT is within 43°F (6°C) of each other.
Average MAF for sample period is less than 28 gm/s.
System voltage is 8-18 volts.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-introduction__on-board-diagnostic-obd-system-check) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Turn ignition on, engine off. Using scan tool, read HO2S 2 voltage. If voltage is greater than 600 mV or less than 300 mV, see «DIAGNOSTIC AIDS»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p0135-p0204) . If voltage is not as specified, go to next step.
Inspect HO2S 2 ignition feed fuse. If fuse is open, go to step 15 . If fuse is okay, go to next step.
Disconnect HO2S 2 harness connector. Connect a test light between chassis ground and HO2S 2 ignition feed circuit. If test light illuminates, go to next step. If test light does not illuminate, go to step 7 .
Connect test light between HO2S 2 harness connector ignition feed and heater ground circuits. If test light illuminates, go to next step. If test light does not illuminate, go to step 8 .
Allow HO2S 2 to cool for at least 10 minutes. Using DVOM, measure resistance between ignition feed and heater ground circuits at HO2S 2. If resistance is 5-6 ohms, go to step 9 . If resistance is not as specified, go to step 14 .
Repair open HO2S 2 ignition feed circuit. After repairs, go to step 16 .
Repair open HO2S 2 heater ground circuit. After repairs, go to step 16 .
Check for faulty connection at HO2S 2. Repair as necessary. After repairs, go to step 16 . If connection is okay, go to next step.
Turn ignition off. Disconnect PCM harness connectors. Measure resistance of HO2S 2 signal and ground circuits. If resistance on either circuit is greater than 5 ohms, repair open or faulty connection as necessary. After repairs, go to step 16 . If resistance is 5 ohms or less, go to next step.
Check for faulty connection at HO2S 2 harness connector. Repair as necessary. After repairs, go to step 16 . If connection is okay, go to next step.
Check for faulty HO2S 2 ground circuit connection at PCM. Repair as necessary. After repairs, go to step 16 . If connection is okay, go to next step.
Check for faulty HO2S 2 signal circuit connection at PCM. Repair as necessary. After repairs, go to step 16 . If connection is okay, go to next step.
Replace HO2S 2. After repairs, go to step 16 .
Locate and repair short to ground in HO2S 2 ignition feed circuit and replace fuse. After repairs, go to next step.
Allow engine to cool completely. Using scan tool, clear DTCs. Turn ignition on, engine off. Read HO2S 2 voltage. If voltage is greater than 600 mV or less than 300 mV, system is okay. If voltage is not as specified, go to step 2 .

DTC P0141: HO2S 2 HEATER CIRCUIT-SENSOR 2 (3.8L "C", "F", "G", "H" & "W" BODIES)

Note. For circuit reference, see appropriate wiring diagram in WIRING DIAGRAMS article.

When ignition is turned on, battery voltage is supplied to HO2S 2 heater to provide for faster sensor warm-up, thus allowing sensor to become active in a shorter period of time. PCM reads amount of time necessary for sensor to become active after start-up. If PCM determines too much time was required for HO2S 2 to become active, DTC P0141 will set.

For duplication of DTC, ensure

No EVAP system, misfire, fuel trim, fuel injector circuit, TP, IAT, MAP, ECT or MAF sensor DTCs are set.
System voltage is 9-16 volts.
ECT and IAT are less than 95°F (35°C) at start-up.
Difference between ECT and IAT is no greater than 43°F (6°C).
Average MAF for sample period is less than 24 gm/s (VIN K), or less than 27 gm/s (VIN 1).

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-introduction__on-board-diagnostic-obd-system-check) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Turn ignition on, engine off. Using scan tool, read HO2S 2 voltage. If voltage is greater than 0.6 volt or less than 0.3 volt, see «DIAGNOSTIC AIDS»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p0135-p0204__dtc-p0141-ho2s-heater-circuit-bank-1) . If voltage is not as specified, go to next step.
Inspect HO2S 2 ignition feed fuse. If fuse is open, go to step 15 . If fuse is okay, go to next step.
Disconnect HO2S 2 harness connector. Connect a test light between ground and HO2S 2 ignition feed circuit. If test light illuminates, go to next step. If test light does not illuminate, go to step 7 .
Connect test light between HO2S 2 harness connector ignition feed and heater ground circuits. If test light illuminates, go to next step. If test light does not illuminate, go to step 8 .
Allow HO2S 2 to cool for at least 10 minutes. Using DVOM, measure resistance between ignition feed and heater ground circuits at HO2S 2. If resistance is 5-6 ohms, go to step 9 . If resistance is not 5-6 ohms, go to step 14 .
Repair open HO2S 2 ignition feed circuit. After repairs, go to step 16 .
Repair open HO2S 2 heater ground circuit. After repairs, go to step 16 .
Check for faulty connection at HO2S 2. Repair as necessary. After repairs, go to step 16 . If connection is okay, go to next step.
Turn ignition off. Disconnect PCM harness connectors. Measure resistance of HO2S 2 signal and ground circuits. If resistance on either circuit is greater than 5 ohms, repair open or faulty connection as necessary. After repairs, go to step 16 . If resistance is 5 ohms or less, go to next step.
Check for faulty connection at HO2S 2 harness connector. Repair as necessary. After repairs, go to step 16 . If connection is okay, go to next step.
Check for faulty HO2S 2 ground circuit connection at PCM. Repair as necessary. After repairs, go to step 16 . If connection is okay, go to next step.
Check for faulty HO2S 2 signal circuit connection at PCM. Repair as necessary. After repairs, go to step 16 . If connection is okay, go to next step.
Replace HO2S 2. After repairs, go to step 16 .
Locate and repair short to ground in HO2S 2 ignition feed circuit. Replace fuse and go to next step.
Allow engine to cool completely. Using scan tool, clear DTCs. Turn ignition on, engine off. Read HO2S 2 voltage. If voltage is greater than 600 mV or less than 300 mV, system is okay. If voltage is not as specified, go to step 2 .

DTC P0141: HO2S HEATER CIRCUIT-BANK 1, SENSOR 2 (4.3L, 5.0L, 5.7L & 7.4L "C", "G", "K" & "P" SERIES)

Note. For circuit reference, see appropriate wiring diagram in WIRING DIAGRAMS article.

HO2S 2 heater provides for faster sensor warm-up allowing sensor to become active in a shorter period of time and remain active during long extended idle. DTC P0141 determines if HO2S 2 heater is operating properly by monitoring amount of time necessary for HO2S 2 to become active after start-up.

For duplication of DTC, ensure system voltage is 11.7-18 volts, MAF is less than 35 gm/s (27 gm/s on 4.3L), engine run time is greater than 2 seconds, ECT and IAT is less than 91°F (33°C), and difference between ECT and IAT is less than 41°F (5°C).

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-introduction__on-board-diagnostic-obd-system-check) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Ensure HO2S 2 is cool. Install scan tool. Turn ignition on, with engine off. Monitor HO2S voltage for 2 minutes using scan tool. If HO2S voltage gradually increases or decreases by 150 mV from initial voltage at key on, see «DIAGNOSTIC AIDS»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p0135-p0204) . If HO2S voltage does not respond as specified, go to next step.
DTC is intermittent. Check for faulty HO2S or intermittent opens or poor connections in HO2S 2 circuits. Repair as necessary. After repairs, go to step 14 . If no problem is found, see «DIAGNOSTIC AIDS»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p0135-p0204) .
Turn ignition off. Disconnect HO2S 2 harness connector. Connect test light between HO2S 2 heater ignition feed and ground circuits at HO2S 2 harness connector. Turn ignition on. If test light illuminates, go to next step. If test light does not illuminate, go to step 6 .
Remove test light. Using jumper wires, jumper HO2S 2 low circuit and high signal circuit to ground. Monitor HO2S 2 voltage with scan tool. If voltage is less than 20 mV, go to step 8 . If voltage is not less than 20 mV, go to step 7 .
Using a test light connected to ground, probe HO2S 2 heater ignition feed circuit. If test light illuminates, go to step 9 . If test light does not illuminate, go to step 10 .
Turn ignition off. Disconnect VCM harness connector containing HO2S 2 low circuit and high signal circuit. Measure resistance of HO2S 2 low circuit and high signal circuit between HO2S 2 and VCM. If resistance of each circuit is less than 5 ohms, go to step 12 . If resistance of both circuits is not less than 5 ohms, go to step 11 .
Replace HO2S 2. After repairs, go to step 14 .
Repair open in HO2S 2 heater ground circuit. After repairs, go to step 14 .
Repair no voltage condition on HO2S 2 heater ignition feed circuit. After repairs, go to step 14 .
Repair high resistance in affected circuit. After repairs, go to step 14 .
Check for faulty VCM harness connections. Repair as necessary. After repairs, go to step 14 .
Replace VCM. Program replacement VCM using required equipment. Perform Passlock® reprogramming and CKP system variation learn procedures. After repairs, go to next step.
Ensure HO2S 2 is cool. Turn ignition on, with engine off. Monitor HO2S voltage for 2 minutes using scan tool. If HO2S voltage gradually increases or decreases by 150 mV from initial voltage at key on, go to next step. If HO2S voltage does not respond as specified, go to step 4 .
Using scan tool, select CAPTURE INFO, REVIEW INFO. If any undiagnosed DTCs are displayed, go to applicable DTC test. If no undiagnosed DTCs are displayed, system is okay.

DTC P0141: HO2S HEATER CIRCUIT-BANK 1, SENSOR 2 (4.8L, 5.3L, & 6.0L "C" & "K" SERIES & 5.7L "F" & "Y" BODIES)

Note. For circuit reference, see appropriate wiring diagram in WIRING DIAGRAMS article.

PCM supplies a bias voltage (about 450 mV) on HO2S 2 high and low signal circuits. When ignition is turned on, battery voltage is supplied to HO2S 2 heater. As heater reaches operating temperature, HO2S 2 voltage responds by changing from bias voltage range to normal operation (less than 300 mV). Depending on exhaust gas content, it is possible for HO2S 2 voltage to be greater than 450 mV.

PCM will only run heater test only on a cold start, depending on cumulative airflow, and only once an ignition cycle. When engine is started, PCM will monitor HO2S 2 voltage. When HO2S 2 goes more than or less than bias range threshold, PCM will determine how much time it took. If PCM detects that it took too much time for HO2S 2 to enter into normal operating range, DTC P0141 will set. The time it takes HO2S 2 to reach operating temperature is based on amount of air that flows into engine.

For duplication of DTC, ensure

DTCs P0101, P0102, P0103, P0112, P0113, P0117, P0118, P0121, P0122, P0123, P0125, P0200, P0335, P0336, P0351-P0358 or P1258 are not set.
ECT and IAT are less than 122°F (50°C) and within 46°F (8°C) of each other at start-up.
Ignition voltage is 10-18 volts.
AIR, EGR and catalyst diagnostics are not active.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-introduction__on-board-diagnostic-obd-system-check) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
If engine has been operating, allow engine to cool down for at least one hour before proceeding with test. Turn engine off. Turn ignition on, with engine off. Using scan tool, select ENGINE 1 DATA LIST and monitor HO2S 2 voltage. If HO2S 2 goes from bias voltage to less than 300 mV or greater than 700 mV, see «DIAGNOSTIC AIDS»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p0135-p0204) . If HO2S 2 does not go to bias voltage or less than 300 mV or greater than 700 mV, go to next step.
Check HO2S 2 ignition feed fuse. If fuse is open, go to step 11 . If fuse is okay, go to next step.
Raise and support vehicle. Disconnect HO2S 2 harness connector. Using a test light connected to ground, probe ignition feed circuit at HO2S 2 harness connector. If test light illuminates, go to next step. If test light does not illuminate, go to step 7 .
Connect test light between HO2S 2 ignition feed and heater ground circuit. If test light illuminates, go to next step. If test light does not illuminate, go to step 8 .
Using DVOM, measure resistance between HO2S 2 ignition feed and heater ground circuits at HO2S 2 pigtail. If resistance is 3.5-14.0 ohms, go to step 9 . If resistance is not as specified, go to step 10 .
Repair open in HO2S 2 ignition feed circuit. After repairs, go to step 12 .
Repair open in HO2S 2 heater ground circuit. After repairs, go to step 12 .
Check for poor HO2S 2 harness connection. Repair as necessary. After repairs, go to step 12 . If connections are okay, go to next step.
Replace HO2S 2. After repairs, go to step 12 .
Repair short to ground in HO2S 2 ignition feed circuit and replace fuse. After repairs, go to next step.
Using scan tool, clear DTCs. Start and warm engine to normal operating temperature. Select DTC, SPECIFIC, and then enter DTC P0141. Operate vehicle within conditions that set DTC. If scan tool indicates that this test ran and passed, go to next step. If scan tool does not indicate that this test ran and passed, go to step 2 .
Using scan tool, select CAPTURE INFO, REVIEW INFO function. If any undiagnosed DTCs are displayed, diagnose affected DTCs. If no undiagnosed DTCs are displayed, system is okay.

The heater diagnostic will only run on a cold start and only once per ignition cycle. Oxygen supply inside HO2S 2 is necessary for proper operation and is provided through HO2S 2 wires. Check all HO2S 2 wires and connections for breaks or contamination.

DTC P0143: HO2S CIRCUIT-LOW VOLTAGE-BANK 1, SENSOR 3 (3.8L "F" BODY)

Note. For circuit reference, see appropriate wiring diagram in WIRING DIAGRAMS article.

Three-Way Catalyst (TWC) system is used to control emissions. PCM uses signal from HO2S 3 behind TWC to read efficiency of TWC. PCM will set DTC P0143 if TWC oxygen storage capacity is less than a predetermined threshold.

For duplication of DTC, ensure

No misfire, transmission, fuel injector circuit, fuel trim, EVAP system, EGR, MAF, TP, IAT, MAP or ECT sensor DTCs are set.
Closed loop commanded air/fuel ratio is 14.5-14.8:1.
Throttle angle is 3-40 percent.
Engine coolant temperature is greater than 167°F (75°C).

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-introduction__on-board-diagnostic-obd-system-check) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Start engine and allow it to reach normal operating temperature. Operate vehicle under conditions required to set DTC. Using scan tool, read HO2S 3 voltage. If voltage remains less than 75 mV, go to step 4 . If voltage does not remain less than 75 mV, go to next step.
Turn engine off. Turn ignition on, engine off. Using scan tool, read and record FAILURE RECORDS data. Operate vehicle within conditions noted in FAILURE RECORDS data. Using scan tool, read SPECIFIC DTC. If scan tool displays DTC P0143 FAILED THIS IGN, go to next step. If scan tool does not display DTC P0143 FAILED THIS IGN, see «DIAGNOSTIC AIDS»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p0135-p0204) .
Disconnect HO2S 3 harness connector. Connect jumper wire between HO2S 3 harness connector ground circuit and chassis ground. If voltage is about 450 mV, see «DIAGNOSTIC AIDS»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p0135-p0204) . If voltage is not as specified, go to next step.
Turn ignition off. Disconnect PCM harness connectors. Check HO2S 3 sensor harness connector signal circuit for short to ground or short to sensor ground. If short is found, go to next step. If circuit is okay, go to step 7 .
Repair HO2S 3 signal circuit. After repairs, go to step 8 .
Replace PCM. Program replacement PCM using required equipment. After repairs, go to next step.
Turn ignition on, engine off. Using scan tool, read and record FAILURE RECORDS data, and clear DTCs. Operate vehicle within conditions noted in FAILURE RECORDS data. Using scan tool, select SPECIFIC DTC INFO for DTC P0143. If scan tool displays DTC P0143 FAILED THIS IGN, go to step 2 . If scan tool does not display DTC P0143 FAILED THIS IGN, system is okay.

Ensure HO2S 3 sensor harness is routed correctly and not contacting exhaust system. Check for faulty PCM grounds. Check fuel system. See BASIC FUEL SYSTEM CHECKS in appropriate BASIC DIAGNOSTIC PROCEDURES article. Perform injector balance test. See appropriate SYSTEM & COMPONENT TESTING article.

Check for vacuum leaks at intake manifold, throttle body, EGR system and crankcase ventilation system. Check for exhaust leaks in front of HO2S 3. Disconnect MAF sensor connector and see if lean condition is corrected. If lean condition is corrected, replace MAF sensor. Check for fuel contamination.

DTC P0143: HO2S CIRCUIT-LOW VOLTAGE-BANK 1, SENSOR 3 (4.0L "G" BODY & 4.6L "E" & "K" BODIES)

Note. For circuit reference, see appropriate wiring diagram in WIRING DIAGRAMS article.

PCM provides a.45 volt reference signal to the HO2S 3 through the Bank 1 high signal circuit. When HO2S 3 is cold, less than 392°F (200°C), the sensor signal voltage will be bias voltage of.45 volt and PCM will keep the system in "open loop". When HO2S 3 is warm, sensor voltage will swing from rich to lean rapidly, at least one switch every 2 seconds, if PCM is in good control of air/fuel mixture.

If sensor remains at a lean voltage for a predetermined amount of time during this test, DTC P0143 will set. DTC will also set when there is a sensor circuit fault giving a false lean indication or air/fuel ratio is actually lean due to a vacuum leak or fuel control system fault.

For duplication of DTC, ensure

DTCs P0101, P0102, P0103, P0107, P0108, P0117, P0118, P0121, P0122, P0123, P0131, P0132, P0133, P0134, P0151, P0152, P0153, P0154, P0300, P1133, P1134, P1153 and P1154 are not set.
TP sensor angle is 5.4-25 degrees.
Engine coolant temperature is 179°F (81.5°C) or greater.
Closed loop fuel control is enabled.
Oxygen sensors are ready.
Engine speed is 800 RPM or greater.
MAP sensor is greater than 32 kPa.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-introduction__on-board-diagnostic-obd-system-check) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Using scan tool, check if DTC P0146 is also present. Diagnose DTC P0146 first, if present. If DTC P0146 is not present, go to next step.
Start and warm engine until coolant temperature is at least 185°F (85°C). Using scan tool, select ENGINE 1 and note HO2S 3 voltage. If voltage remains at less than.05 volt for 30 seconds or more, go to next step. If voltage does not remain at.05 volt or less for 30 seconds or more, fault is not present. See «DIAGNOSTIC AIDS»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p0135-p0204) .
Turn ignition off. Disconnect HO2S 3 harness connector. Start engine. Using DVOM, measure voltage between HO2S 3 terminals "A" and "B". If voltage remains at less than.05 volt for 30 seconds or more, go to step 9 . If voltage does not remain at.05 volt or less for 30 seconds or more, go to next step.
Store fluid life index as indicated in scan tool. Turn ignition off. Wait 30 seconds, and then disconnect PCM harness connector C1. Using DVOM, measure resistance to ground at HO2S 3 harness connector terminal "B". If resistance is greater than 10,000 ohms, go to next step. If resistance is not greater than 10,000 ohms, go to step 7 .
Measure resistance between HO2S 3 harness connector terminals "A" and "B". If resistance is 5 ohms or less, go to step 8 . If resistance is not 5 ohms or less, go to step 10 .
Repair short to ground in HO2S 3 high signal circuit.
Repair HO2S 3 high and low signal circuit for short together.
Replace HO2S 3.
Replace PCM. Program replacement PCM using required equipment.

Check snapshot data for front long and rear long term fuel trim values. If both banks were lean, check for a condition that would cause lean engine operation. If only the rear bank was lean, check for a condition that would cause only the rear bank to be lean, such as an intermittent short to ground in HO2S 3 high signal circuit. DO NOT solder oxygen sensor wires.

DTC P0143: HO2S CIRCUIT-LOW VOLTAGE-BANK 1, SENSOR 3 (4.3L, 5.0L & 5.7L "C", "G", "K", "L", "M", "P", "S" & "T" SERIES)

Note. For circuit reference, see appropriate wiring diagram in WIRING DIAGRAMS article.

VCM supplies a voltage of about.45 volt between HO2S 3 signal and HO2S 3 ground circuits. HO2S 3 varies voltage from about one volt with rich exhaust to 0.1 volt with lean exhaust. HO2S 3 produces no voltage and acts as an open circuit when temperature is less than 600°F (316°C). DTC P0143, DTC P0144, an open sensor circuit or a cold sensor causes open loop operation. DTC P0143 determines if HO2S 3 or circuit is shorted low by checking for a lean condition during steady throttle and power enrichment.

For duplication of DTC, ensure no active misfire, EVAP system, TP, IAT, MAP, ECT or MAF sensor DTCs are set, no intrusive tests are in progress, no device controls are active, and system voltage is 11.7-18 volts.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-introduction__on-board-diagnostic-obd-system-check) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Install scan tool. Warm engine to normal operating temperature. Place gear selector in Park or Neutral. Apply parking brake. Increase engine speed to 1200 RPM. Monitor HO2S 3 voltage using scan tool. If voltage is fixed at less than 26 mV, go to step 4 . If HO2S 3 voltage is not fixed at less than 26 mV, go to next step.
DTC is intermittent. Check for additional DTCs. If no additional DTCs are set, see «DIAGNOSTIC AIDS»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p0135-p0204) . If any additional DTCs are set, diagnose affected DTCs.
Turn ignition off. Disconnect HO2S 3 harness connector. Connect a jumper wire between HO2S 3 ground circuit of HO2S 3 connector (VCM side) and ground. Turn ignition on, with engine off. Monitor HO2S 3 voltage using scan tool. If voltage is 351-551 mV, go to next step. If voltage is not 351-551 mV, go to step 6 .
Check for any condition that may cause HO2S 3 to detect a lean condition. Repair as necessary. After repairs, go to step 10 . If no problems are found, go to step 8 .
Turn ignition off. Remove jumper wire. Disconnect VCM harness connector containing HO2S 3 high signal circuit. Check for continuity between HO2S 3 high signal circuit and ground, and then between HO2S 3 high signal circuit and HO2S 3 ground circuit. If continuity is present, go to next step. If continuity is not present, go to step 9 .
Repair HO2S 3 high circuit for short to ground or HO2S 3 ground circuit. After repairs, go to step 10 .
Replace HO2S 3. After repairs, go to step 10 .
Replace VCM. Program replacement VCM using required equipment. After repairs, go to next step.
Using scan tool, clear DTCs. Start and warm engine to normal operating temperature. Select DTC, SPECIFIC, and then enter this DTC. Operate vehicle within the conditions for setting this DTC. If scan tool indicates that this test ran and passed, go to next step. If scan tool does not indicate that this test ran and passed, go to step 2 .
Using scan tool, select CAPTURE INFO, REVIEW INFO. If any undiagnosed DTCs are displayed, go to applicable DTC test. If no undiagnosed DTCs are displayed, system is okay.

Using scan tool, observe Long Term (LT) fuel trim values at different RPM and air flow conditions. Scan tool should display fuel trim cells so that LT fuel trim values can be checked in each cell to determine when DTC may have set. If DTC is set, LT fuel trim values will be about 158 or greater.

Check for mispositioned HO2S 3 wire pigtail contacting exhaust manifold. Check for intermittent ground in wire between connector and sensor. Check for poor VCM to engine block ground. Check for lean fuel injectors. Check for water near in-tank fuel pump inlet that may be delivered to injectors. Water causes a lean exhaust and can cause DTC to set.

System will be lean if fuel pressure is too low. Monitor fuel pressure while driving vehicle at various speeds and loads to verify pressure. Check for an exhaust leak that can cause outside air to be pulled into exhaust and past sensor. Check for vacuum or crankcase leaks that can cause a lean condition and possibly high idle. If all listed checks are okay, HO2S 3 is faulty. DO NOT solder HO2S 3 wires.

DTC P0144: HO2S CIRCUIT-HIGH VOLTAGE-BANK 1, SENSOR 3 (3.8L "F" BODY)

Note. For circuit reference, see appropriate wiring diagram in WIRING DIAGRAMS article.

Three-Way Catalyst (TWC) system is used to control emissions. PCM uses signal from Heated Oxygen Sensor 3 (HO2S 3) behind TWC to read efficiency of TWC. PCM will set DTC P0144 if HO2S 3 signal voltage remains excessively high for an extended period of time.

For duplication of DTC, ensure no misfire, fuel injector circuit, fuel trim, EVAP system, CKP, MAF, TP, IAT, MAP, EGR or ECT DTCs are set, system is in closed loop with commanded air/fuel ratio of 14.5-14.8:1, and throttle position is 3-40 percent.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-introduction__on-board-diagnostic-obd-system-check) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Start engine and allow it to reach operating temperature. Operate vehicle under conditions required to set DTC. Using scan tool, read HO2S 3 voltage. If voltage remains greater than.999 volt, go to step 4 . If voltage does not remain greater than.999 volt, go to next step.
Turn ignition on. Using scan tool, read and record FAILURE RECORDS data. Operate vehicle within conditions noted in FAILURE RECORDS data. Using scan tool, select SPECIFIC DTC INFO for DTC P0144. If scan tool displays DTC P0144 FAILED THIS IGN, go to next step. If scan tool does not display DTC P0144 FAILED THIS IGN, see «DIAGNOSTIC AIDS»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p0135-p0204) .
Disconnect HO2S 3 harness connector. Connect a jumper wire between HO2S 3 harness connector ground circuit and chassis ground. If voltage is about 0.45 volt, see «DIAGNOSTIC AIDS»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p0135-p0204) . If voltage is not as specified, go to next step.
Turn ignition off. Disconnect PCM harness connectors. Turn ignition on. Using DVOM, measure voltage between PCM harness connector HO2S 3 signal circuit and chassis ground. If voltage is greater than.999 volt, go to next step. If voltage is not greater than.999 volt, go to step 7 .
Repair short to voltage in HO2S 3 signal circuit. After repairs, go to step 8 .
Replace PCM. Program replacement PCM using required equipment. After repairs, go to next step.
Turn ignition on, engine off. Using scan tool, read and record FAILURE RECORDS data, and clear DTCs. Operate vehicle within conditions noted in FAILURE RECORDS data. Using scan tool, select SPECIFIC DTC INFO for DTC P0144. If scan tool displays DTC P0144 FAILED THIS IGN, go to step 2 . If scan tool does not display DTC P0144 FAILED THIS IGN, system is okay.

Ensure HO2S 3 sensor harness is routed correctly and not contacting exhaust system. Check for open or short in HO2S 3 signal or ground circuits. Check for internally shorted HO2S 3. Check HO2S 3 for silicone (powdery white deposit) contamination. Check for faulty PCM grounds. Check fuel system. See BASIC FUEL SYSTEM CHECKS in appropriate BASIC DIAGNOSTIC PROCEDURES article. Perform injector balance test. See appropriate SYSTEM & COMPONENT TESTING article.

DTC P0144: HO2S CIRCUIT-HIGH VOLTAGE-BANK 1, SENSOR 3 (4.0L "G" BODY & 4.6L "E" & "K" BODIES)

Note. For circuit reference, see appropriate wiring diagram in WIRING DIAGRAMS article.

PCM provides a.45 volt reference signal to the HO2S 3 through the Bank 1 high signal circuit. When HO2S 3 is cold, less than 392°F (200°C), the sensor signal voltage will be about.45 volt and PCM will keep the system in "open loop". When HO2S 3 is warm, sensor will swing from rich to lean rapidly, at least one switch every 2 seconds, if PCM is in good control of air/fuel mixture.

If sensor remains at rich voltage for greater than 40 seconds during this test, DTC P0144 will set. DTC will also set when there is a sensor circuit fault giving a false rich indication or air/fuel ratio is actually rich due to a fuel control system fault.

For duplication of DTC, ensure

DTCs P0101, P0102, P0103, P0107, P0108, P0117, P0118, P0121, P0122, P0123, P0131, P0132, P0133, P0134, P0151, P0152, P0153, P0154, P0300, P1133, P1134, P1153 and P1154 are not set.
TP sensor angle is 5.4-25 degrees.
Coolant temperature is 179°F (81.5°C) or greater.
Closed loop fuel control is enabled.
Oxygen sensors are ready.
Engine speed is 800 RPM or greater.
MAP sensor is greater than 32 kPa.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-introduction__on-board-diagnostic-obd-system-check) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Using scan tool, check if DTC P0146 is also present. Diagnose DTC P0146 first, if present. If DTC P0146 is not present, go to next step.
Start and warm engine until coolant temperature is at 185°F (85°C) or greater. Using scan tool, select ENGINE 1 and note HO2S 3 voltage. If voltage remains at.9 volt or greater for 30 seconds or more, go to next step. If voltage does not remain at.9 volt or greater for 30 seconds or more, fault is not present. See «DIAGNOSTIC AIDS»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p0135-p0204) .
Turn engine off. Disconnect HO2S 3 harness connector. Start engine. Using DVOM, measure voltage between sensor terminals "A" and "B". If voltage remains greater than.9 volt for 30 seconds or more, go to step 7 . If voltage does not remain greater than.9 volt for 30 seconds or more, go to next step.
Store fluid life index as indicated in scan tool. Turn ignition off and wait 30 seconds, and then disconnect PCM harness connector C1. Turn ignition on. Using DVOM, measure voltage between ground and HO2S 3 signal circuit at PCM harness connector. If voltage is greater than 0.1 volt, go to next step. If reading is not greater than 0.1 volt, go to step 8 .
Repair short to voltage in HO2S 3 signal circuit.
Replace HO2S 3.
Replace PCM. Program replacement PCM using required equipment.

Check snapshot data for front long and rear long term fuel trim values. If both banks were rich, check for a condition that would cause a rich engine operation. DO NOT solder HO2S 3 wires.

DTC P0144: HO2S CIRCUIT-HIGH VOLTAGE-BANK 1, SENSOR 3 (4.3L, 5.0L & 5.7L "C", "G", "K", "L", "M", "P", "S" & "T" SERIES)

Note. For circuit reference, see appropriate wiring diagram in WIRING DIAGRAMS article.

VCM supplies a voltage of about.45 volt between HO2S 3 signal and HO2S 3 ground circuits. HO2S 3 varies voltage from about one volt with rich exhaust to 0.1 volt with lean exhaust. HO2S 3 produces no voltage and acts as an open circuit when temperature is less than 600°F (316°C). DTC P0143, DTC P0144, an open sensor circuit or a cold sensor causes open loop operation. DTC P0144 determines if HO2S 3 or circuit is shorted high by checking for a rich condition during steady throttle.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-introduction__on-board-diagnostic-obd-system-check) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Install scan tool. Warm engine to normal operating temperature. Place gear selector in Park or Neutral. Apply parking brake. Increase engine speed to 1200 RPM. Monitor HO2S 3 voltage using scan tool. If HO2S 3 voltage is fixed at greater than.994 volt, go to step 4 . If HO2S 3 voltage is not fixed at greater than.994 volt, go to next step.
DTC is intermittent. Check if additional DTCs are set. Diagnose affected DTCs. If no additional DTCs are set, see «DIAGNOSTIC AIDS»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p0135-p0204) .
Turn ignition off. Disconnect HO2S 3 harness connector. Using a jumper wire, jumper HO2S 3 ground circuit to ground. Turn ignition on, with engine off. Monitor HO2S 3 voltage using scan tool. If voltage is 351-551 mV, go to next step. If voltage is not 351-551 mV, go to step 6 .
HO2S 3 is detecting a rich condition. Check for cause of rich condition. Repair as necessary. After repairs, go to step 10 . If no problem is found, go to step 8 .
Turn ignition off. Remove jumper wire. Disconnect VCM harness connector containing HO2S 3 signal circuit. Turn ignition on, with engine off. Measure voltage between ground and HO2S 3 signal circuit at VCM harness connector. If voltage is greater than 20 mV, go to next step. If voltage is not greater than 20 mV, go to step 9 .
Repair short to voltage in HO2S 3 signal circuit. After repairs, go to step 10 .
Replace HO2S 3. After repairs, go to step 10 .
Replace VCM. Program replacement VCM using required equipment. Perform Passlock® reprogramming and CKP system variation learn procedures. After repairs, go to next step.
Using scan tool, clear DTCs. Start and warm engine to normal operating temperature. Select DTC, SPECIFIC, and then enter this DTC. Operate vehicle within the conditions for setting this DTC. If scan tool indicates that this test ran and passed, go to next step. If scan tool does not indicate that this test ran and passed, go to step 2 .
Using scan tool, select CAPTURE INFO, REVIEW INFO. If any undiagnosed DTCs are displayed, go to applicable DTC test. If no undiagnosed DTCs are displayed, system is okay.

Check for an intermittent TP sensor output that will cause system to go rich due to false indication of throttle moving. Check for false rich indication due to silicone contamination of HO2S 3 indicated by DTC accompanied by lean driveability conditions and a powdery White deposit on sensor.

Check for internally shorted HO2S 3 as indicated by a voltage of greater than one volt on scan tool. Disconnect HO2S 3. If voltage changes from greater than one volt to about.45 volt, replace HO2S 3. DO NOT solder HO2S 3 wires.

DTC P0146: HO2S CIRCUIT-INSUFFICIENT ACTIVITY-BANK 1, SENSOR 3 (3.8L "F" BODY)

Note. For circuit reference, see appropriate wiring diagram in WIRING DIAGRAMS article.

Three-Way Catalyst (TWC) system is used to control emissions. PCM uses signal from Heated Oxygen Sensor 3 (HO2S 3) behind TWC to read efficiency of TWC. PCM will set DTC P0146 if TWC oxygen storage capacity is less than a predetermined threshold.

For duplication of DTC, ensure no misfire, fuel injector, fuel trim, EVAP system, EGR, CKP, MAF, TP, IAT, MAP or ECT DTCs are set, and engine has been running for more than 4 minutes.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-introduction__on-board-diagnostic-obd-system-check) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Warm engine to normal operating temperature. Place gear selector in Park or Neutral. Apply parking brake. Increase engine speed to greater than 1200 RPM for 2 minutes. Using scan tool, read HO2S 3 voltage. If voltage is not switching from greater than 475 mV to less than 425 mV, go to next step. If voltage is switching as specified, go to step 4 .
Turn engine off. Turn ignition on, engine off. Using scan tool, read and record FAILURE RECORDS data. Operate vehicle within conditions noted in FAILURE RECORDS data. Using scan tool, read SPECIFIC DTC. If scan tool displays DTC P0146 FAILED THIS IGN, go to next step. If scan tool does not display DTC P0146 FAILED THIS IGN, see «DIAGNOSTIC AIDS»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p0135-p0204) .
Disconnect HO2S 3 harness connector. Connect a jumper wire between chassis ground and HO2S 3 harness connector high signal and low circuits. If voltage is less than 150 mV, go to step 8 . If voltage is not less than 150 volt, go to next step.
Remove jumper wire from HO2S 3 high signal circuit, leaving jumper wire at low circuit connected. Using DVOM, measure voltage between HO2S 3 harness connector high signal and heater ground circuits. If voltage is about 4.5 volts, go to next step. If voltage is not as specified, go to step 7 .
Turn ignition off. Disconnect PCM harness connectors. Measure resistance of HO2S 3 harness connector low circuit. If resistance is greater than 5 ohms, repair open or faulty connection as necessary. After repairs, go to step 13 . If resistance is not greater than 5 ohms, go to step 9 .
Turn ignition off. Disconnect PCM harness connectors. Measure resistance of HO2S 3 harness connector high signal circuit. If resistance is greater than 5 ohms, repair open or faulty connection as necessary. After repairs, go to step 13 . If resistance is not greater than 5 ohms, go to step 10 .
Check for faulty connection at HO2S 3. Repair as necessary. After repairs, go to step 13 . If connection is okay, go to step 11 .
Check HO2S 3 low circuit for faulty connection at PCM. Repair as necessary. After repairs, go to step 13 . If PCM connection is okay, go to step 12 .
Check HO2S 3 high signal circuit for faulty connection at PCM. Repair as necessary. After repairs, go to step 13 . If connection is okay, go to step 12 .
Replace HO2S 3. After repairs, go to step 13 .
Replace PCM. Program replacement PCM using required equipment. After repairs, go to next step.
Using scan tool, read and record FAILURE RECORDS data, and clear DTCs. Operate vehicle within conditions noted in FAILURE RECORDS data. Using scan tool, select SPECIFIC DTC INFO for DTC P0146. If scan tool displays DTC P0146 FAILED THIS IGN, go to step 2 . If scan tool does not display DTC P0146 FAILED THIS IGN, system is okay.

Check for faulty connections or damaged harness. If connections and harness appear okay, observe scan tool while moving all related harnesses and connectors. A change in scan tool display indicates fault location. Check HO2S 3 heater operation.

DTC P0146: HO2S CIRCUIT-INSUFFICIENT ACTIVITY-BANK 1, SENSOR 3 (4.0L "G" BODY & 4.6L "E" & "K" BODIES)

Note. For circuit reference, see appropriate wiring diagram in WIRING DIAGRAMS article.

PCM provides a.45 volt reference signal to the HO2S 3 through the Bank 1 high signal circuit. When HO2S 3 reaches operating temperature, it will generate a counter voltage that will vary based on the amount of oxygen in the exhaust. A lean exhaust will generate a low voltage and cause the reference voltage (.45 volt) to decrease. A rich exhaust will generate a high voltage and cause the reference voltage to increase. If sensor cannot respond under the test conditions and generate a voltage greater than.61 volt or less than.31 volt, DTC P0146 will set.

For duplication of DTC, ensure DTCs P0117, P0118, P0122 and P0123 are not set, coolant temperature is 167°F (75°C) or greater, TP sensor angle is 2.2-81.6 degrees, calculated throttle position switch is open, and engine speed is 800-3000 RPM.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-introduction__on-board-diagnostic-obd-system-check) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Start and warm engine until coolant temperature reaches 185°F (85°C) or greater. Using scan tool, select ENGINE 1 and note bank 1 sensor 3 voltage display for 30 seconds. If voltage remains.3-.6 volt, go to next step. If voltage does not remain.3-.6 volt, fault is not present at this time.
Turn ignition off. Disconnect HO2S 3 harness connector. Start engine. Using DVOM, measure voltage between HO2S 3 harness connector terminals "A" and "B". If voltage remains.3-.6 volt, go to step 6 . If voltage does not remain.3-.6 volt, go to next step.
Store fluid life index as indicated on scan tool. Turn ignition off for 30 seconds, and then disconnect PCM harness connector C1. Using DVOM, measure resistance between HO2S 3 high signal circuit at PCM connector and HO2S 3 harness connector terminal "B". If resistance is 5 ohms or less, go to next step. If resistance is not 5 ohms or less, go to step 8 .
Measure resistance between PCM harness connector C1 HO2S 3 low circuit and HO2S 3 harness connector terminal "A". If resistance is 5 ohms or less, go to step 13 . If resistance is greater than 5 ohms, go to step 9 .
Turn ignition on, with engine off. Measure voltage between HO2S 3 harness connector terminals "C" and "D". If voltage reading is 10.5 volts or greater, go to step 12 . If voltage reading is less than 10.5 volts, go to next step.
Measure voltage between HO2S 3 harness connector terminal "D" to ground. If voltage is 10.5 volts or greater, go to step 10 . If reading is less than 10.5 volts or greater, go to step 11 .
Repair open in HO2S 3 high signal circuit.
Repair open in HO2S 3 low circuit.
Repair open in HO2S 3 ground circuit.
Repair open or short to ground in HO2S 3 ignition feed circuit.
Replace HO2S 3.
Check terminal contacts at PCM harness connector C1. Repair as necessary. If terminal contacts are okay, go to next step.
Replace PCM. Program replacement PCM using required equipment.

DO NOT solder oxygen sensor wires. Check for poorly grounded or loosely mounted HO2S 3.

DTC P0146: HO2S CIRCUIT-INSUFFICIENT ACTIVITY-BANK 1, SENSOR 3 (4.3L, 5.0L & 5.7L "C", "G", "K, "L", "M", "P", "S" & "T" SERIES)

Note. For circuit reference, see appropriate wiring diagram in WIRING DIAGRAMS article.

HO2S 3 heater provides for faster sensor warm-up, allowing sensor to become active in a shorter period of time and remain active during long extended idle. DTC P0146 determines if HO2S 3 or HO2S 3 circuit is open.

For duplication of DTC, ensure

No EVAP system, misfire, TP, IAT, MAP, ECT or MAF sensor DTCs are set.
No intrusive tests are in progress.
No device controls are active.
System voltage is 11.7-18 volts.
Engine run time is greater than 2 minutes.
Deceleration fuel cut-off mode is not active.
ECT is 137°F (58°C) or greater.
MAF is 13 gm/s.
System is in closed loop.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-introduction__on-board-diagnostic-obd-system-check) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Using scan tool, clear DTCs and reset fuel trim values. Start engine and allow it to reach normal operating temperature. Monitor HO2S 3 voltage with scan tool. If voltage is fixed at 399-473 mV, go to step 4 . If voltage is not as specified, go to next step.
DTC is intermittent. If any other DTCs are set, go to applicable DTC test. If no other DTCs are set, see «DIAGNOSTIC AIDS»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p0135-p0204) .
Turn ignition off. Disconnect HO2S 3 harness connector. Using jumper wires, jumper HO2S 3 high signal and low circuits to ground. Turn ignition on. Monitor HO2S 3 voltage with scan tool. If voltage is less than 20 mV, go to step 7 . If voltage is not less than 20 mV, go to next step.
Turn ignition off. Remove jumper wires. Disconnect VCM harness connector containing HO2S 3 high signal and low circuits. Measure resistance of HO2S 3 high signal and low circuits between HO2S 3 and VCM harness connectors. If resistance of each circuit is less than 5 ohms, go to next step. If resistance of each circuit is not less than 5 ohms, go to step 9 .
Check for poor connections at VCM. Repair as necessary. After repairs, go to step 17 . If connections are okay, go to step 16 .
Remove jumper wires from HO2S 3 terminals. Ensure ignition is on. Connect test light between heater ignition feed and heater ground circuits at HO2S 3 harness connector. If test light illuminates, go to next step. If test light does not illuminate, go to step 10 .
Turn ignition off. Reconnect HO2S 3 harness connector. Disconnect VCM harness connectors containing HO2S 3 low circuit and VCM ground circuit. Measure resistance between HO2S 3 low circuit and one of the VCM ground circuits. If resistance is less than 500 ohms, go to step 12 . If resistance is not less than 500 ohms, go to step 11 .
Repair circuit that measured high resistance. After repairs, go to step 17 .
Repair HO2S 3 heater ignition feed or ground circuit. After repairs, go to step 17 .
Repair high resistance between HO2S 3 low circuit and VCM ground circuit. After repairs, go to step 17 .
Check for exhaust leaks upstream of HO2S 3. Repair as necessary. After repairs, go to step 17 . If no leaks are found, go to next step.
Allow engine to completely cool. Measure resistance between HO2S 3 low circuit and one of the VCM ground circuits. If resistance is less than 500 ohms, go to step 15 . If resistance is not less than 500 ohms, go to next step.
Remove HO2S 3. Clean mounting threads, apply anti-seize compound and reinstall. Measure resistance between HO2S 3 low circuit and one of the VCM ground circuits. If resistance is less than 500 ohms, go to step 17 . If resistance is not less than 500 ohms, go to next step.
Replace HO2S 3. After repairs, go to step 17 .
Replace VCM. Program replacement VCM using required equipment. Perform Passlock® reprogramming and CKP system variation learn procedures. After repairs, go to next step.
Using scan tool, clear DTCs. Start and warm engine to normal operating temperature. Select DTC, SPECIFIC, and then enter this DTC. Operate vehicle within the conditions for setting this DTC. If scan tool indicates that this test ran and passed, go to next step. If scan tool does not indicate that this test ran and passed, go to step 2 .
Using scan tool, select CAPTURE INFO, REVIEW INFO. If any undiagnosed DTCs are displayed, go to applicable DTC test. If no undiagnosed DTCs are displayed, system is okay.

With ignition on and engine off, HO2S 3 voltage on scan tool should gradually decrease to less than.15 volt, indicating heater is operating properly. If voltage does not decrease as specified, disconnect HO2S 3 harness connector and connect a test light between HO2S 3 harness connector terminals "C" and "D" (engine harness side). If test light illuminates, replace HO2S 3. If test light does not illuminate, repair open in HO2S 3 heater ground circuit or HO2S 3 ignition feed circuit.

Using scan tool, monitor signal voltage while wiggling HO2S 3 related connectors and wiring harness with a warm engine running at part throttle in closed loop. If a failure is induced, signal voltage will change from normal fluctuating voltage of greater than.6 volt and less than.3 volt, to a fixed voltage of about.45 volt. A change in voltage will assist in isolating location of fault. DO NOT solder HO2S 3 wires.

DTC P0147: HO2S HEATER CIRCUIT-BANK 1, SENSOR 3 (3.8L "F" BODY)

Note. For circuit reference, see appropriate wiring diagram in WIRING DIAGRAMS article.

When ignition is turned on, battery voltage is supplied to HO2S 3 heater to provide for faster sensor warm-up, thus allowing sensor to become active in a shorter period of time. PCM reads amount of time necessary for sensor to become active after start-up. If PCM determines too much time was required for HO2S 3 to become active, DTC P0147 will set.

For duplication of DTC, ensure

No misfire, fuel injector, fuel trim, EVAP system, CKP, MAF, TP, IAT, MAP, ERG or ECT sensor DTCs are set.
System voltage is 9-18 volts.
ECT and IAT are less than 95°F (35°C) at start-up.
Difference between ECT and IAT is not greater than 11°F (6°C).
Average MAF is less than 22.7 gm/s.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-introduction__on-board-diagnostic-obd-system-check) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Turn ignition on, engine off. Using scan tool, read HO2S 3 voltage. If voltage is greater than 0.6 volt or less than 0.3 volt, see «DIAGNOSTIC AIDS»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p0135-p0204) . If voltage is not greater than 0.6 volt or less than 0.3 volt, go to next step.
Inspect HO2S 3 ignition feed fuse. If fuse is open, go to step 15 . If fuse is okay, go to next step.
Turn ignition off. Raise and support vehicle. Disconnect HO2S 3 harness connector. Connect a test light between chassis ground and HO2S 3 ignition feed circuit. If test light illuminates, go to next step. If test light does not illuminate, go to step 7 .
Connect test light between HO2S 3 harness connector ignition feed and heater ground circuits. If test light illuminates, go to next step. If test light does not illuminate, go to step 8 .
Allow HO2S 3 to cool down for at least 10 minutes. Using DVOM, measure resistance between ignition feed and heater ground circuits at HO2S 3 pigtail. If resistance is 5-10 ohms, go to step 9 . If resistance is not as specified, go to step 14 .
Repair open HO2S 3 ignition feed circuit. After repairs, go to step 16 .
Repair open HO2S 3 heater ground circuit. After repairs, go to step 16 .
Check for faulty connection at HO2S 3. Repair as necessary. After repairs, go to step 16 . If connection is okay, go to next step.
Turn ignition off. Disconnect PCM harness connectors. Measure resistance of HO2S 3 signal and ground circuits. If resistance on either circuit is greater than 5 ohms, repair open or faulty connection as necessary. After repairs, go to step 16 . If resistance is not greater than 5 ohms, go to next step.
Check for faulty connection at HO2S 3 harness connector. Repair as necessary. After repairs, go to step 16 . If connection is okay, go to next step.
Check for faulty HO2S 3 ground circuit connection at PCM. Repair as necessary. After repairs, go to step 16 . If connection is okay, go to next step.
Check for faulty HO2S 3 signal circuit connection at PCM. Repair as necessary. After repairs, go to step 16 . If connection is okay, go to next step.
Replace HO2S 3. After repairs, go to step 16 .
Locate and repair short to ground in HO2S 3 ignition feed circuit and replace fuse. After repairs, go to next step.
Allow engine to cool completely. Using scan tool, clear DTCs. Turn ignition on, engine off. Read HO2S 3 voltage. If voltage is greater than 0.6 volt or less than 0.3 volt, system is okay. If voltage is not as specified, go to step 2 .

DTC P0147: HO2S HEATER CIRCUIT-BANK 1, SENSOR 3 (4.0L "G" BODY & 4.6L "E" & "K" BODIES)

Note. For circuit reference, see appropriate wiring diagram in WIRING DIAGRAMS article.

This test determines if the heating element in the post-converter oxygen sensor is working properly. Oxygen sensor voltage is produced when the sensor reaches operating temperature and when the oxygen content of the exhaust stream is different than that in the atmosphere. The heating element is energized through the ignition signal circuit, when ignition is turned on, allowing sensor to reach operating temperature quickly. This in turn allows the PCM to enter "closed loop" quicker. The voltage that the PCM measures on the oxygen sensor high and low inputs is called bias voltage. When bias voltage takes too long to vary (greater or less than bias voltage) after ignition is turned on, DTC P0147 will set.

For duplication of DTC, ensure

DTCs P0101, P0102, P0103, P0117, P0118 and P0146 are not set.
ECT decreased at least 50°F (10°C) from end of last ignition cycle to beginning of this ignition cycle.
Average post-converter HO2S 3 bias voltage is 352-546 mV.
Engine did not stall during test.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-introduction__on-board-diagnostic-obd-system-check) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Turn ignition on, with engine off. Disconnect HO2S 3 harness connector. Using DVOM, measure voltage between sensor harness connector terminals "C" and "D". If voltage is greater than 10.5 volts, go to next step. If voltage is not greater than 10.5 volts, go to step 4 .
Using a jumper wire, jumper sensor connector terminal "D" to harness connector terminal "D". Set DVOM to amp scale. Connect DVOM in series with sensor connector terminal "C" to harness connector terminal "C". If DVOM reads 0.9-1.5 amps, go to step 5 . If DVOM does not read 0.9-1.5 amps, go to step 8 .
Check voltage from harness connector terminal "D" to ground. If reading is 10.5 volts or greater, go to step 6 . If reading is not 10.5 volts or greater, go to step 7 .
Using scan tool, select FREEZE FRAME data and operate vehicle under the same conditions which set the DTC. If DTC resets, go to step 8 . If DTC does not reset, fault is not present. See «DIAGNOSTIC AIDS»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p0135-p0204) .
Repair open in HO2S 3 ground circuit.
Repair open or short to ground in HO2S 3 ignition feed circuit.
Replace HO2S 3.

An intermittent open in HO2S 3 ignition signal circuit or ground circuit may cause DTC to set. A malfunctioning pre-converter HO2S may also set DTC. DO NOT solder oxygen sensor wires.

DTC P0147: HO2S HEATER CIRCUIT BANK 1, SENSOR 3 (4.3L, 5.0L & 5.7L "C", "G", "K", "L", "M", "P", "S" & "T" SERIES)

Note. For circuit reference, see appropriate wiring diagram in WIRING DIAGRAMS article.

HO2S 3 heater provides for faster sensor warm-up allowing sensor to become active in a shorter period of time and remain active during long extended idle. DTC test determines if HO2S 3 heater is operating properly by monitoring amount of time necessary for HO2S 3 to become active after start-up. If VCM fails to detect HO2S 3 voltage transitions greater than or less than bias range within a specified amount of time, DTC P0147 will set.

For duplication of DTC, ensure system voltage is 11.7-17 volts, MAF is less than 27 gm/s, engine run time is greater than 2 seconds, ECT and IAT is less than 90°F (32°C), and difference between ECT and IAT is not greater than 41°F (5°C).

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-introduction__on-board-diagnostic-obd-system-check) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Install scan tool. Turn ignition on, with engine off. Immediately record HO2S 3 voltage using scan tool, and then continue to monitor voltage for 2 minutes. If voltage gradually increases or decreases by 150 mV, go to next step. If voltage does not gradually increase or decrease by 150 mV, go to step 4 .
Condition required to set DTC is not present at this time. Check for intermittent opens or high resistance in HO2S 3 circuits. Check for poor VCM harness connections. Repair as necessary. After repairs, go to step 14 . If no problem was found, see «DIAGNOSTIC AIDS»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p0135-p0204) .
Turn ignition off. Disconnect HO2S 3 harness connector. Turn ignition on. Connect test light between heater ignition feed and ground circuits at HO2S 3 harness connector. If test light illuminates, go to next step. If test light does not illuminate, go to step 6 .
Remove test light. Using jumper wires, jumper HO2S 3 high signal circuit and low circuit to ground. Monitor HO2S 3 voltage with scan tool. If voltage is less than 20 mV, go to step 8 . If voltage is not less than 20 mV, go to step 7 .
Using a test light connected to ground, probe heater ignition feed circuit at HO2S 3 harness connector. If test light illuminates, go to step 9 . If test light does not illuminate, go to step 10 .
Turn ignition off. Remove jumper wires. Disconnect VCM harness connector containing HO2S 3 high signal circuit and low circuit. Measure resistance of high signal circuit and low circuit between VCM and HO2S 3. If resistance of each circuit is less than 5 ohms, go to step 12 . If resistance of each circuit is not less than 5 ohms, go to step 11 .
Replace HO2S 3. After repairs, go to step 14 .
Repair open HO2S 3 heater ground circuit. After repairs, go to step 14 .
Repair no voltage condition on HO2S 3 heater ignition feed circuit. After repairs, go to step 14 .
Repair circuit that measured high resistance. After repairs, go to step 14 .
Check for faulty VCM harness connections. Repair as necessary. After repairs, go to step 14 . If connections are okay, go to next step.
Replace VCM. Program replacement VCM using required equipment. Perform Passlock® reprogramming and CKP system variation learn procedures. After repairs, go to next step.
Allow engine to cool for about 30 minutes. Turn ignition on, engine off. Using scan tool, immediately record HO2S 3 voltage, and then continue to monitor voltage for 2 minutes. If voltage gradually increases or decreases by 150 mV, go to next step. If voltage does not gradually increase or decrease by 150 mV, go to step 4 .
Using scan tool, select CAPTURE INFO, REVIEW INFO. If any undiagnosed DTCs are displayed, go to affected DTC test. If no additional DTCs are present, system is okay.

DTC P0150: HO2S CIRCUIT-BANK 2, SENSOR 1 (3.0L "V" BODY)

Note. For circuit reference, see appropriate wiring diagram in WIRING DIAGRAMS article.

For duplication of DTC, ensure DTCs P0201, P0202, P0203, P0204, P0205, P0206, P0410, P0411, P0412, P0440, P0441, P0442, P0443, P0450 or P0455 are not set, HO2S 1 heater remains on for more than 200 seconds, and secondary AIR diagnostics are not running.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-introduction__on-board-diagnostic-obd-system-check) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Start engine and operate to normal operating temperature. Using scan tool, monitor HO2S 1 voltage. If voltage remains less than 399 mV, go to step 4 . If voltage does not remain less than 399 mV, go to next step.
Turn ignition on, with engine off. Review FREEZE FRAME data for this DTC and note parameters. Clear DTCs. Turn ignition off for 15 seconds. Start engine and operate vehicle as close to conditions recorded in FREEZE FRAME as possible. Check for DTCs. If DTC P0150 is set, go to next step. If DTC P0150 is not set, see «DIAGNOSTIC AIDS»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p0135-p0204) .
Turn ignition on, with engine off. Disconnect HO2S 1 harness connector. Check for signs of water or corrosion. Repair as necessary. If HO2S 1 voltage on scan tool is 375-525 mV, go to step 14 . If HO2S 1 voltage on scan tool is not 375-525 mV, go to next step.
Using DVOM, measure voltage between ground and signal circuit at HO2S 1 harness connector. If voltage is 900-1100 mV, go to next step. If voltage is not 900-1100 mV, go to step 11 .
Using DVOM, measure voltage between ground and low circuit at HO2S 1 harness connector. If voltage is 700-800 mV, go to step 22 . If voltage is not 700-800 mV, go to next step.
Continue to monitor voltage on HO2S 1 low circuit between harness connector and ground. Disconnect the 3 other HO2S harness connectors. As each sensor is disconnected, recheck voltage. If disconnecting one of the other sensors restores voltage to 700-800 mV, go to step 14 . If disconnecting the other sensors does not restore voltage to 700-800 mV, go to next step.
Leave all HO2S disconnected. Turn ignition off. Disconnect ECM harness connector. Turn ignition on. Using DVOM, check for voltage between ground and HO2S 1 low circuit at ECM harness connector. If any voltage is present, go to step 15 . If no voltage is present, go to next step.
Using DVOM, check harness continuity of HO2S 1 low circuit. If continuity is present, go to next step. If continuity is not present, go to step 16 .
Using DVOM, check harness continuity between HO2S 1 low circuit and ground. If continuity is present, go to step 17 . If continuity is not present, go to step 21 .
Leave all HO2S disconnected. Turn ignition off. Disconnect ECM harness connector located in engine compartment relay center. Turn ignition on. Using DVOM, check for voltage between ground and HO2S 1 signal circuit at ECM harness connector. If any voltage is present, go to step 18 . If no voltage is present, go to next step.
Using DVOM, check harness continuity of HO2S 1 signal circuit. If continuity is present, go to next step. If continuity is not present, go to step 19 .
Using DVOM, check harness continuity between HO2S 1 signal circuit and ground. If continuity is present, go to step 20 . If continuity is not present, go to step 21 .
Replace shorted HO2S 1. After repairs, go to step 23 .
Repair short to voltage in HO2S 1 low circuit. After repairs, go to step 23 .
Repair open or high resistance in HO2S 1 low circuit. After repairs, go to step 23 .
Repair short to ground in HO2S 1 low circuit. After repairs, go to step 23 .
Repair short to voltage in HO2S 1 signal circuit. After repairs, go to step 23 .
Repair open or high resistance in HO2S 1 signal circuit. After repairs, go to step 23 .
Repair short to ground in HO2S 1 signal circuit. After repairs, go to step 23 .
Check for poor connections and terminal tension at ECM harness connector. Repair as necessary. After repairs, go to step 23 . If connections and terminals are okay, go to next step.
Replace ECM. New ECM must be programmed with theft deterrent module frequency code currently on vehicle. After repairs, go to next step.
Using scan tool, clear DTCs. Turn ignition off for 15 seconds. Start engine and operate vehicle as close to conditions recorded in FREEZE FRAME as possible. Check for DTCs. If DTC P0150 is set, go to step 2 . If DTC P0150 is not set, go to next step.
If other DTCs were present during OBD system check and have not been diagnosed, go to applicable DTC. If no other DTCs are present, system is okay.

HO2S 1 pigtail or harness may be mispositioned and contacting exhaust system. Inspect harness connectors for backed-out terminals, improper mating, broken locks, improperly formed or damaged terminals, poor terminal-to-wire connection, corrosion or water intrusion.

An oxygen supply inside HO2S 1 is necessary for proper operation. This supply of oxygen is provided through HO2S 1 wiring harness. All HO2S 1 wires and connections should be inspected for breaks or contamination. Repair as necessary.

Inspect for poor ECM-to-engine grounds. If fuel pressure is too low, this DTC may set. Check for lean injectors. Inspect for disconnected or damaged vacuum hoses and for vacuum leaks at intake manifold, throttle body and crankcase ventilation system.

An exhaust leak may cause outside air to be pulled into exhaust gas stream past HO2S 1, causing this DTC to set. Check for exhaust leaks near HO2S 1.

DTC P0151: HO2S CIRCUIT VOLTAGE LOW BANK 2, SENSOR 1 (3.0L "V" BODY)

Note. For circuit reference, see appropriate wiring diagram in WIRING DIAGRAMS article.

Heated Oxygen Sensor 1 (HO2S 1) is a wide range-type sensor that calculates amount of oxygen in exhaust stream more accurately than a toggling-type sensor. This HO2S 1 operates more like an air fuel sensor. ECM supplies.28 volt to sensor and uses this voltage as a reference to amount of oxygen in exhaust system. When system is lean, oxygen level will be high and reference voltage will also be high. When oxygen level is low, reference voltage will also be low. ECM monitors variation in voltage and attempts to maintain voltage constant by increasing or decreasing amount of current flow to HO2S 1. Using this information allows ECM to maintain proper air/fuel ratio. If ECM detects that the standardized dynamic value from HO2S 1 is less than 0.6 volt, DTC P0151 will set.

For duplication of DTC, ensure

Engine load is between 20 and 40 percent.
Engine speed is 1400-2400 RPM.
Air/fuel ratio is between.94 and 1.06.
DTCs P0300-P0306, P0171, P0172, P0175, P0443, P0446 and P0460 are not set.
Secondary air diagnosis is not running.
There is no maximum or minimum closed loop fuel control.
There is no EVAP high loading indicated.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-introduction__on-board-diagnostic-obd-system-check) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Check for exhaust leaks between HO2S 1 and HO2S 2. If leaks are found, go to step 10 . If no leaks are found, go to next step.
Turn ignition off. Disconnect right-side HO2S 1. Inspect connectors for contamination. If connection is faulty, go to step 11 . If connection is okay, go to next step.
Disconnect ECM harness connectors. Measure resistance of circuit between terminal No. 6 of HO2S 1 and terminal No. 29 of ECM. Also measure resistance of circuit between terminal No. 1 of HO2S 1 and terminal No. 11 of ECM. If resistance of either circuit is less than 2 ohms, go to step 13 . If resistance of neither circuit is less than 2 ohms, go to next step.
If either circuit had no continuity, go to step 12 . If both circuits had continuity, go to next step.
Turn ignition on. Measure voltage between ground and terminal No. 5 (B+ circuit) at ECM harness connector. If battery voltage is present, go to next step. If battery voltage is not present, go to step 13 .
Measure resistance of HO2S 1 heater control circuit between HO2S 1 and ECM. If resistance is 0-2 ohms, go to step 9 . If resistance is not as specified, go to next step.
Repair open or short in circuit. After repairs, go to step 14 .
Replace right-side HO2S 1. After repairs, go to step 14 .
Repair leaks as necessary. After repairs, go to step 14 .
Repair terminals as necessary. After repairs, go to step 14 .
Repair open in affected circuit. After repairs, go to step 14 .
Repair short to ground in affected circuit. After repairs, go to next step.
Using scan tool, clear DTCs. Start engine and allow it to reach normal operating temperature. Select DTC and SPECIFIC DTC function, and then enter this DTC. Operate vehicle within conditions required to set this DTC until scan tool indicates this diagnostic ran. If scan tool indicates this diagnostic passed, go to next step. If scan tool indicates this diagnostic failed, go to step 2 .
Using scan tool, select CAPTURE INFO, REVIEW INFO. If any undiagnosed DTCs are displayed, go to applicable DTC test. If no undiagnosed DTCs are displayed, system is okay.

An oxygen supply inside HO2S 1 is necessary for proper operation. This supply of oxygen is provided through HO2S 1 wires. All HO2S 1 wires and connections should be inspected for breaks or contamination. Repair as necessary. Inspect for poor ECM to engine ground connections.

DTC P0151: HO2S CIRCUIT VOLTAGE LOW BANK 2, SENSOR 1 (3.8L "F" BODY)

Note. For circuit reference, see appropriate wiring diagram in WIRING DIAGRAMS article.

For duplication of DTC, ensure no misfire, fuel injector circuit, fuel trim, EVAP system, EGR, CKP, MAF, TP, IAT, MAP or ECT sensor DTCs are set, commanded air/fuel ratio is 14.5-14.8:1, and throttle angle is 3-40 percent.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-introduction__on-board-diagnostic-obd-system-check) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Warm engine to operating temperature. Operate vehicle under conditions required to set DTC. Using scan tool, read HO2S 1 voltage. If voltage remains less than 0.3 volt, go to step 4 . If voltage does not remain less than 0.3 volt, go to next step.
Turn ignition on, engine off. Using scan tool, read and record FAILURE RECORDS data. Operate vehicle within conditions noted in FAILURE RECORDS data. Using scan tool, read SPECIFIC DTC. If scan tool displays DTC P0151 FAILED THIS IGN, go to next step. If scan tool does not display DTC P0151 FAILED THIS IGN, see «DIAGNOSTIC AIDS»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p0135-p0204) .
Disconnect HO2S 1 harness connector. Connect a jumper wire between HO2S 1 harness connector ground circuit and chassis ground. If voltage is about 0.45 volt, see «DIAGNOSTIC AIDS»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p0135-p0204) . If voltage is not as specified, go to next step.
Turn ignition off. Disconnect PCM harness connectors. Check HO2S 1 sensor harness connector signal circuit for short to ground or short to sensor ground circuit. If short is found, go to next step. If circuit is okay, go to step 7 .
Repair circuit as necessary. After repairs, go to step 8 .
Replace PCM. Program replacement PCM using required equipment. After repairs, go to next step.
Turn ignition on, engine off. Using scan tool, read and record FAILURE RECORDS data, and clear DTCs. Operate vehicle within conditions noted in FAILURE RECORDS data. Using scan tool, select SPECIFIC DTC INFO for DTC P0151. If scan tool displays DTC P0151 FAILED THIS IGN, go to step 2 . If scan does not display DTC P0151 FAILED THIS IGN, system is okay.

Ensure HO2S 1 harness is routed correctly and not contacting exhaust system. Check for faulty PCM grounds. Check fuel system. See BASIC FUEL SYSTEM CHECKS in appropriate BASIC DIAGNOSTIC PROCEDURES article. Perform injector balance test. See appropriate SYSTEM & COMPONENT TESTING article.

DTC P0151: HO2S CIRCUIT-LOW VOLTAGE-BANK 2, SENSOR 1 (4.0L "G" BODY & 4.6L "E" & "K" BODIES)

Note. For circuit reference, see appropriate wiring diagram in WIRING DIAGRAMS article.

PCM provides a.45 volt reference signal to the HO2S 1 through the Bank 2 high signal circuit. When HO2S 1 is cold, less than 392°F (200°C), the sensor signal voltage will be about.45 volt and PCM will keep the system in "open loop". When HO2S 1 is warm, system will go into closed loop operation and PCM takes control of air/fuel mixture. If HO2S 1 voltage indicates a lean condition during this time for more than 40 seconds, DTC P0151 will set.

For duplication of DTC, ensure

DTCs P0101, P0102, P0103, P0107, P0108, P0117, P0118, P0121, P0122, P0123, P0152 or P0154 are not set.
TP sensor angle is 5.4-25 degrees.
Coolant temperature is 179°F (81.5°C) or greater.
Closed loop fuel control is enabled.
Oxygen sensors are ready.
Engine speed is 800 RPM or greater.
MAP sensor is greater than 32 kPa.
DTC P0131 test runs and passes.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-introduction__on-board-diagnostic-obd-system-check) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Using scan tool, check if DTC P0154 is also present and diagnose first. If DTC P0154 is not present, go to next step.
If DTC was set because vehicle ran out of fuel, system is okay. Clear DTC. If vehicle did not run out of fuel, go to next step.
Warm engine until coolant is at least 185°F (85°C). Using scan tool, note bank 2 sensor 1 voltage. If voltage remains less than.3 volt for 30 seconds or more, go to next step. If voltage does not remain less than.3 volt for 30 seconds or more, fault is not present at this time. See «DIAGNOSTIC AIDS»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p0135-p0204) .
Turn ignition off. Disconnect HO2S 1 harness connector. Start engine. Measure voltage between HO2S 1 terminals "A" and "B". If voltage remains less than.3 volt for 30 seconds or more, diagnose using DTC P0153 test. If voltage does not remain.3 volt or less for 30 seconds or more, go to next step.
Store fluid life index as indicated in scan tool. Turn ignition off and wait 30 seconds. Disconnect PCM harness connector C2. Measure resistance to ground at HO2S 1 harness connector terminal "B". If resistance is greater than 10,000 ohms, go to next step. If resistance is not greater than 10,000 ohms, go to step 8 .
Measure resistance between HO2S 1 harness connector terminals "A" and "B". If resistance is 5 ohms or less, go to step 9 . If resistance is not 5 ohms or less, go to step 10 .
Repair short to ground in HO2S 1 high signal circuit.
Repair HO2S 1 high signal and low circuits shorted to each other.
Check HO2S 1 high signal and low circuits for poor terminal contact at PCM harness connector C2. Repair as necessary. If connections are okay, go to next step.
Replace PCM. Program replacement PCM using required equipment.

Check snapshot data for front long and rear long term fuel trim values. If both banks were lean, check for a condition that would cause lean engine operation. If only the front bank was lean, check for a condition that would cause only the front bank to be lean, such as an intermittent short to ground in HO2S 1 high signal circuit. DO NOT solder oxygen sensor wires.

DTC P0151: HO2S CIRCUIT-LOW VOLTAGE-BANK 2, SENSOR 1 (4.3L, 5.0L, 5.7L & 7.4L "C", "G", "K", "L", "M", "P", "S" & "T" SERIES)

Note. For circuit reference, see appropriate wiring diagram in WIRING DIAGRAMS article.

VCM supplies a voltage of about.45 volt between HO2S 1 signal and HO2S 1 ground circuits. HO2S 1 varies voltage from about one volt with rich exhaust to 0.1 volt with lean exhaust. HO2S 1 produces no voltage and acts as an open circuit when temperature is less than 600°F (316°C). DTC P0151, DTC P0152, an open sensor circuit or a cold sensor causes open loop operation. If VCM detects low HO2S 1 voltage for more than 50 seconds, DTC P0151 will set.

For duplication of DTC, ensure no misfire, EVAP system, TP, IAT, MAP, ECT or MAF sensor DTCs are set, no intrusive tests are in progress, no device controls are active, and system voltage is 11.7-18 volts.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-introduction__on-board-diagnostic-obd-system-check) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Install scan tool. Warm engine to normal operating temperature. Place gear selector in Park or Neutral. Apply parking brake. Increase engine speed to 1200 RPM. Monitor HO2S 1 voltage using scan tool. If voltage is fixed less than.086 volt (86 mV), go to step 4 . If voltage is not fixed less than.086 volt (86 mV), go to next step.
Condition required to set DTC is not present at this time. Check for intermittent HO2S 1 circuit faults or any condition that may cause HO2S 1 to detect a lean condition. Repair as necessary. After repairs, go to step 10 . If no problems are found, see «DIAGNOSTIC AIDS»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p0135-p0204) .
Turn ignition off. Disconnect HO2S 1 harness connector. Using a jumper wire, jumper HO2S 1 low circuit to ground. Turn ignition on, with engine off. Monitor HO2S 1 voltage using scan tool. If voltage is.35-.55 volt (350-550 mV), go to next step. If voltage is not.35-.55 volt (350-550 mV), go to step 6 .
Check for any condition that may cause HO2S 1 to detect a lean condition. Repair as necessary. After repairs, go to step 10 . If no problems are found, go to step 8 .
Turn ignition off. Remove jumper wire. Disconnect VCM harness connector containing HO2S 1 high signal circuit. Check for continuity between HO2S 1 high signal circuit and ground, and then between HO2S 1 high signal circuit and low circuit. If both checks indicate no continuity, go to step 9 . If either check indicates continuity, go to next step.
Repair HO2S 1 high signal circuit for short to ground or short to HO2S 1 low circuit. After repairs, go to step 10 .
Replace HO2S 1. After repairs, go to step 10 .
Replace VCM. Program replacement VCM using required equipment. Perform Passlock® reprogramming and CKP system variation learn procedures. After repairs, go to next step.
Using scan tool, clear DTCs. Start and warm engine to normal operating temperature. Select DTC, SPECIFIC, and then enter this DTC. Operate vehicle within the conditions for setting this DTC. If scan tool indicates that this test ran and passed, go to next step. If scan tool does not indicate that this test ran and passed, go to step 2 .
Using scan tool, select CAPTURE INFO, REVIEW INFO. If any undiagnosed DTCs are displayed, go to applicable DTC test. If no undiagnosed DTCs are displayed, system is okay.

Check for mispositioned HO2S 1 wire pigtail contacting exhaust manifold. Check for intermittent ground in wire between connector and sensor. Check for poor VCM-to-engine block ground. Check for lean fuel injectors. Check for water near in-tank fuel pump inlet that may be delivered to injectors. Water causes a lean exhaust and can cause DTC to set.

System will be lean if fuel pressure is too low. Monitor fuel pressure while driving vehicle at various speeds and loads to verify pressure. Check for an exhaust leak that can cause outside air to be pulled into exhaust and past sensor. Check for vacuum or crankcase leaks that can cause a lean condition and possibly high idle. If all listed checks are okay, HO2S 1 is faulty. DO NOT solder HO2S 1 wires.

DTC P0151: HO2S CIRCUIT-LOW VOLTAGE-BANK 2, SENSOR 1 (4.8L, 5.3L & 6.0L "C" & "K" SERIES & 5.7L "F" & "Y" BODIES)

Note. For circuit reference, see appropriate wiring diagram in WIRING DIAGRAMS article.

PCM supplies about 450 millivolts (mV) between HO2S 1 high and low signal circuits. The HO2S 1 voltage ranges from about 1000 mV when exhaust is rich to about 10 mV when exhaust is lean. PCM monitors and stores sensor voltage information and evaluates voltage samples to determine amount of time sensor voltage is out of range. If PCM detects HO2S 1 voltage is less than predetermined voltage, DTC P0151 will set.

For duplication of DTC, ensure

DTCs P0101, P0102, P0103, P0112, P0113, P0117, P0118, P0121, P0122, P0123, P0125, P0200, P0335, P0336, P0351-P0358 or P1258 are not set.
AIR, EGR and catalyst diagnostics are not active.
Ignition voltage is greater than 9 volts.
Fuel system is operating in "closed loop".
Fuel trim learn is enabled.
TP sensor angle is between 2 and 70 percent.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-introduction__on-board-diagnostic-obd-system-check) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Start and warm engine to normal operating temperature. Using scan tool, select ENGINE 1 DATA LIST and monitor HO2S 1 voltage, with engine at idle. If voltage is less than 200 mV, go to step 4 . If voltage is not less than 200 mV, go to next step.
Turn ignition on, with engine off. Using scan tool, review FREEZE FRAME and/or FAILURE RECORDS data and note parameters. Turn ignition off for about 15 seconds. Start engine and operate vehicle within conditions required for this diagnostic to run, and as close to conditions recorded in FREEZE FRAME/FAILURE RECORDS as possible. Select DTC function, and then enter DTC P0151. If scan tool indicates that this test failed this ignition, go to next step. If scan tool does not indicate that this test failed this ignition, see «DIAGNOSTIC AIDS»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p0135-p0204) .
Disconnect HO2S 1 connector. Connect a fused jumper wire between PCM connector (harness side), HO2S 1 low circuit and ground. If sensor voltage is 350-550 mV, see «DIAGNOSTIC AIDS»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p0135-p0204) . If sensor voltage is not 350-550 mV, go to next step.
Turn ignition off. Disconnect PCM harness connector C1. Check HO2S 1 signal circuit for short to ground or short to sensor ground circuit. Repair circuit as necessary. After repairs, go to next step. If circuit(s) are okay, go to step 7 .
Repair HO2S 1 signal circuit. After repairs, go to step 8 .
Replace PCM. Program replacement PCM using required equipment. After repairs, go to next step.
Using scan tool, clear DTCs. Start and warm engine to normal operating temperature. Select DTC, SPECIFIC, and then enter DTC P0131. Operate vehicle within conditions for setting this DTC. If scan tool indicates that this test ran and passed, go to next step. If scan tool does not indicate that this test ran and passed, go to step 2 .
Using scan tool, select CAPTURE INFO, REVIEW INFO function. If any undiagnosed DTCs are displayed, go to applicable DTC test. If no undiagnosed DTCs are displayed, system is okay.

Check for HO2S 1 pigtail wire for breaks, contamination or grounding on exhaust manifold. Check for intermittent ground in signal wire between sensor connector and sensor.

Check for lean injector(s). Perform injector balance test. See appropriate SYSTEM & COMPONENT TESTING article. Check for fuel contamination, improper fuel pressure or exhaust leak, especially near HO2S 1. Check for vacuum or crankcase leak, causing a lean condition.

DTC P0152: HO2S CIRCUIT-HIGH VOLTAGE-BANK 2, SENSOR 1 (3.0L "V" BODY)

Note. For circuit reference, see appropriate wiring diagram in WIRING DIAGRAMS article.

Heated Oxygen Sensor 1 (HO2S 1) is a wide range-type sensor that calculates amount of oxygen in exhaust stream more accurately than a toggling-type sensor. This HO2S 1 operates more like an air fuel sensor. ECM supplies.28 volt to sensor and uses this voltage as a reference to amount of oxygen in exhaust system. When system is lean, oxygen level will be high and reference voltage will also be high. When oxygen level is low, reference voltage will also be low. ECM monitors variation in voltage and attempts to maintain voltage constant by increasing or decreasing amount of current flow to HO2S 1. Using this information allows ECM to maintain proper air/fuel ratio. If ECM detects that lamda offset is greater than.03, DTC P0132 will set.

For duplication of DTC, ensure engine is running and rear HO2S sensor diagnostic is not running.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-introduction__on-board-diagnostic-obd-system-check) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Start engine and operate to normal operating temperature. Using scan tool, monitor HO2S 1 voltage. If voltage on scan tool remains greater than 1083 mV, go to step 4 . If voltage on scan tool does not remain greater than 1083 mV, go to next step.
Turn ignition on, with engine off. Review FREEZE FRAME data for this DTC and note parameters. Clear DTCs. Turn ignition off for 15 seconds. Start engine and operate vehicle as close to conditions recorded in FREEZE FRAME as possible. Check for DTCs. If DTC P0152 is set, go to next step. If DTC P0152 is not set, see «DIAGNOSTIC AIDS»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p0135-p0204) .
Turn ignition on, with engine off. Disconnect HO2S 1 harness connector. Check for signs of water or corrosion. Repair as necessary. If HO2S 1 voltage on scan tool is 375-525 mV, go to step 14 . If HO2S 1 voltage on scan tool is not 375-525 mV, go to next step.
Using DVOM, measure voltage between ground and signal circuit at HO2S 1 harness connector. If voltage is 900-1100 mV, go to next step. If voltage is not 900-1100 mV, go to step 11 .
Using DVOM, measure voltage between ground and low circuit at HO2S 1 harness connector. If voltage is 700-800 mV, go to step 22 . If voltage is not 700-800 mV, go to next step.
Continue to monitor voltage on HO2S 1 low circuit between harness connector and ground. Disconnect 3 other HO2S harness connectors. As each sensor is disconnected, recheck voltage. If disconnecting the other sensors restores voltage to 700-800 mV, go to step 14 . If disconnecting one of the other sensors does not restore voltage to 700-800 mV, go to next step.
Leave all HO2S disconnected. Turn ignition off. Disconnect ECM harness connector located in engine compartment, in relay center. Turn ignition on. Using DVOM, check for voltage between ground and HO2S 1 low circuit at ECM harness connector. If any voltage is present, go to step 15 . If no voltage is present, go to next step.
Using DVOM, check harness continuity of HO2S 1 low circuit. If continuity is present, go to next step. If continuity is not present, go to step 16 .
Using DVOM, check harness continuity between HO2S 1 low circuit and ground. If continuity is present, go to step 17 . If continuity is not present, go to step 21 .
Leave all HO2S harness connectors disconnected. Turn ignition off. Disconnect ECM harness connector located in engine compartment, in relay center. Turn ignition on. Using DVOM, check for voltage between ground and HO2S 1 signal circuit at ECM harness connector. If any voltage is present, go to step 18 . If no voltage is present, go to next step.
Using DVOM, check harness continuity of HO2S 1 signal circuit. If continuity is present, go to next step. If continuity is not present, go to step 19 .
Using DVOM, check harness continuity between HO2S 1 signal circuit and ground. If continuity is present, go to step 20 . If continuity is not present, go to step 21 .
Replace shorted HO2S 1. After repairs, go to step 23 .
Repair short to voltage in HO2S 1 low circuit. After repairs, go to step 23 .
Repair open or high resistance in HO2S 1 low circuit. After repairs, go to step 23 .
Repair short to ground in HO2S 1 low circuit. After repairs, go to step 23 .
Repair short to voltage in HO2S 1 signal circuit. After repairs, go to step 23 .
Repair open or high resistance in HO2S 1 signal circuit. After repairs, go to step 23 .
Repair short to ground in HO2S 1 signal circuit. After repairs, go to step 23 .
Check for poor connections and terminal tension at ECM harness connector. Repair as necessary. After repairs, go to step 23 . If connections and terminals are okay, go to next step.
Replace ECM. New ECM must be programmed with theft deterrent module frequency code currently on vehicle. After repairs, go to next step.
Using scan tool, clear DTCs. Turn ignition off for 15 seconds. Start engine and operate vehicle as close to conditions recorded in FREEZE FRAME as possible. Check for DTCs. If DTC P0152 is set, go to step 2 . If DTC P0152 is not set, go to next step.
If other DTCs were present during OBD system check and have not been diagnosed, go to applicable DTC. If no other DTCs are present, system is okay.

An oxygen supply inside HO2S is necessary for proper operation. This supply of oxygen is provided through HO2S 1 wiring harness. All HO2S 1 wires and connections should be inspected for breaks or contamination. Repair as necessary. Inspect for poor ECM to engine ground connections.

DTC P0152: HO2S CIRCUIT-HIGH VOLTAGE-BANK 2, SENSOR 1 (3.8L "F" BODY)

Note. For circuit reference, see appropriate wiring diagram in WIRING DIAGRAMS article.

PCM provides about 0.45 volt reference to Heated Oxygen Sensor 1 (HO2S 1). Sensor signal voltage varies from about one volt when exhaust is rich to about 0.1 volt when exhaust is lean. PCM reads and stores sensor voltage information and evaluates the voltage samples to determine amount of time sensor voltage is out of range. If HO2S 1 voltage is out of predetermined range, DTC P0151 will set.

For duplication of DTC, ensure no misfire, fuel injector circuit, fuel trim, EVAP system, EGR, CKP, MAF, TP, IAT, MAP or ECT sensor DTCs are set, engine coolant temperature is greater than 167°F (75°C), and closed loop commanded air/fuel ratio is 14.5-14.8:1.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-introduction__on-board-diagnostic-obd-system-check) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Start engine and allow it to reach operating temperature. Operate vehicle under conditions required to set DTC. Using scan tool, read HO2S 1 voltage. If voltage remains greater than 0.8 volt, go to step 5 . If voltage does not remain greater than 0.8 volt, go to next step.
Operate vehicle in deceleration fuel mode (vehicle speed greater than 25 MPH and TP angle less than 3 percent) while monitoring HO2S 1 voltage. If voltage remains greater than 0.11 volt, go to step 5 . If voltage does not remain greater than 0.11 volt, go to next step.
Turn engine off. Turn ignition on, engine off. Using scan tool, read and record FAILURE RECORDS data. Operate vehicle within conditions noted in FAILURE RECORDS data. Using scan tool, read SPECIFIC DTC. If scan tool displays DTC P0152 FAILED THIS IGN, go to next step. If scan tool does not display DTC P0152 FAILED THIS IGN, see «DIAGNOSTIC AIDS»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p0135-p0204) .
Disconnect HO2S 1 harness connector. Connect a jumper wire between HO2S 1 harness connector ground circuit and chassis ground. If voltage is about 0.45 volt, see «DIAGNOSTIC AIDS»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p0135-p0204) . If voltage is not as specified, go to next step.
Turn ignition off. Disconnect PCM harness connectors. Turn ignition on. Using DVOM, measure voltage between PCM harness connector HO2S 1 signal circuit and chassis ground. If voltage is greater than 0.6 volt, go to next step. If voltage is not greater than 0.6 volt, go to step 8 .
Repair short to voltage in HO2S 1 signal circuit. After repairs, go to step 9 .
Replace PCM. Program replacement PCM using required equipment. After repairs, go to next step.
Turn ignition on, engine off. Using scan tool, read and record FAILURE RECORDS data, and clear DTCs. Operate vehicle within conditions noted in FAILURE RECORDS data. Using scan tool, select SPECIFIC DTC INFO for DTC P0152. If scan tool displays DTC P0152 FAILED THIS IGN, go to step 2 . If scan tool does not display DTC P0152 FAILED THIS IGN, system is okay.

Ensure HO2S 1 harness is routed correctly and not contacting exhaust system. Check for open or short in HO2S 1 signal or ground circuits. Check for internally shorted HO2S 1. Check HO2S 1 for silicone (powdery white deposit) contamination. Check for faulty PCM grounds. Check fuel system. See BASIC FUEL SYSTEM CHECKS in appropriate BASIC DIAGNOSTIC PROCEDURES article. Perform injector balance test. See appropriate SYSTEM & COMPONENT TESTING article.

DTC P0152: HO2S CIRCUIT-HIGH VOLTAGE-BANK 2, SENSOR 1 (4.0L "G" BODY & 4.6L "E" & "K" BODIES)

Note. For circuit reference, see appropriate wiring diagram in WIRING DIAGRAMS article.

PCM provides a.45 volt reference signal to the HO2S 1 through the Bank 2 high signal circuit. When HO2S 1 is cold, less than 392°F (200°C), the sensor signal voltage will be about.45 volt and PCM will keep the system in "open loop". When HO2S 1 is warm, sensor will swing from rich to lean rapidly, at least one switch every 2 seconds, if PCM is in good control of air/fuel mixture.

If sensor remains at rich voltage for greater than 40 seconds during this test, DTC P0152 will set. DTC will also set when there is a sensor circuit fault giving a false rich indication or air/fuel ratio is actually rich due to a fuel control system fault.

For duplication of DTC, ensure

DTCs P0101, P0102, P0103, P0107, P0108, P0117, P0118, P0122, P0123, P0152 or P0154 are not set.
TP sensor angle is 5.4-25 degrees.
Coolant temperature is 179°F (81.5°C) or greater.
Closed loop fuel control is enabled.
Oxygen sensors are ready, engine speed is 800 RPM or greater.
MAP sensor is greater than 32 kPa.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-introduction__on-board-diagnostic-obd-system-check) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Using scan tool, check if DTC P0154 is also present and diagnose first. If DTC P0154 is not present, go to next step.
Start and warm engine until coolant temperature is 185°F (85°C) or greater. Using scan tool, note front oxygen sensor voltage. If voltage remains at.6 volt or greater for 30 seconds or more, go to next step. If voltage does not remain at.6 volt or greater for 30 seconds or more, fault is not present. See «DIAGNOSTIC AIDS»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p0135-p0204) .
Turn engine off. Disconnect HO2S 1 harness connector. Start engine. Using DVOM, measure voltage between sensor terminals "A" and "B". If voltage remains greater than.6 volt for 30 seconds or more, diagnose using test for DTC P0153. If voltage does not remain greater than.6 volt for 30 seconds or more, go to next step.
Store fluid life index as indicated in scan tool. Turn ignition off and wait 30 seconds, and then disconnect PCM harness connector C2. Turn ignition on. Measure voltage between ground and HO2S 1 high signal circuit at PCM harness connector. If voltage is greater than 0.1 volt, go to next step. If voltage is not greater than 0.1 volt, go to step 7 .
Repair short to voltage in HO2S 1 high signal circuit.
Check HO2S 1 circuits for poor terminal contact at PCM. Repair as necessary. If connections are okay, go to next step.
Replace PCM. Program replacement PCM using required equipment.

Check snapshot data for front long and rear long term fuel trim values. If both banks were rich, check for a condition that would cause a rich engine operation. DO NOT solder HO2S 1 wires.

DTC P0152: HO2S CIRCUIT VOLTAGE HIGH BANK 2, SENSOR 1 (4.3L, 5.0L, 5.7L & 7.4L "C", "G", "K", "L", "M", "P", "S" & "T" SERIES)

Note. For circuit reference, see appropriate wiring diagram in WIRING DIAGRAMS article.

VCM supplies a voltage of about.45 volt between HO2S 1 signal and HO2S 1 ground circuits. HO2S 1 varies voltage from about one volt with rich exhaust to 0.1 volt with lean exhaust. HO2S 1 produces no voltage and acts as an open circuit when temperature is less than 600°F (316°C). DTC P0151, DTC P0152, an open sensor circuit or a cold sensor causes open loop operation. DTC P0152 determines if HO2S 1 or circuit is shorted high by checking for a rich condition during steady throttle.

For duplication of DTC, ensure no misfire, EVAP system, ECT, IAT, MAF, MAP or TP sensor DTCs are set, no intrusive tests are in progress, no device controls are active, and system voltage is 11.7-18 volts.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-introduction__on-board-diagnostic-obd-system-check) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Install scan tool. Warm engine to normal operating temperature. Place gear selector in Park or Neutral. Apply parking brake. Increase engine speed to 1200 RPM. Monitor HO2S 1 voltage using scan tool. If voltage is not fixed at greater than.976 volt, go to next step. If voltage is fixed at greater than.976 volt, go to step 4 .
Condition required to set DTC is not present at this time. Check for intermittent HO2S 1 circuit faults or any condition that may cause HO2S 1 to detect a rich condition. Repair as necessary. After repairs, go to step 10 . If no problems are found, see «DIAGNOSTIC AIDS»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p0135-p0204) .
Turn ignition off. Disconnect HO2S 1 harness connector. Using a jumper wire, jumper HO2S 1 low circuit to ground. Turn ignition on, with engine off. Monitor HO2S 1 voltage using scan tool. If voltage is about 400 mV, go to next step. If voltage is not about 400 mV, go to step 6 .
Check for contaminated HO2S 1 or any condition that may cause HO2S 1 to detect a rich condition. Repair as necessary. After repairs, go to step 10 . If no problems are found, go to step 8 .
Turn ignition off. Remove jumper wire. Disconnect VCM harness connector containing HO2S 1 high signal circuit. Turn ignition on, with engine off. Measure voltage between ground and HO2S 1 high signal circuit. If voltage is greater than 20 mV, go to next step. If voltage is not greater than 20 mV, go to step 9 .
Repair short to voltage in HO2S 1 high signal circuit. After repairs, go to step 10 .
Replace HO2S 1. After repairs, go to step 10 .
Replace VCM. Program replacement VCM using required equipment. Perform Passlock® reprogramming and CKP system variation learn procedures. After repairs, go to next step.
Using scan tool, clear DTCs. Start and warm engine to normal operating temperature. Select DTC, SPECIFIC, and then enter this DTC. Operate vehicle within the conditions for setting this DTC. If scan tool indicates that this test ran and passed, go to next step. If scan tool does not indicate that this test ran and passed, go to step 2 .
Using scan tool, select CAPTURE INFO, REVIEW INFO. If any undiagnosed DTCs are displayed, go to applicable DTC test. If no undiagnosed DTCs are displayed, system is okay.

Check for an intermittent TP sensor output that will cause system to go rich due to false indication of throttle moving. Check for false rich indication due to silicone contamination of HO2S indicated by DTC accompanied by lean driveability conditions and a powdery white deposit on sensor.

Check for internally shorted HO2S as indicated by a voltage of greater than one volt on scan tool. Disconnect HO2S. If voltage changes from greater than one volt to about.45 volt, replace HO2S. DO NOT solder HO2S wires.

DTC P0152: HO2S CIRCUIT-HIGH VOLTAGE-BANK 2, SENSOR 1 (4.8L, 5.3L & 6.0L "C" & "K" SERIES)

Note. For circuit reference, see appropriate wiring diagram in WIRING DIAGRAMS article.

PCM provides about 0.45 volt reference to HO2S 1. HO2S 1 sensor signal voltage varies from about one volt when exhaust is rich to about 0.1 volt when exhaust is lean. PCM reads and stores sensor voltage information and evaluates the voltage samples to determine amount of time sensor voltage is out of range. If HO2S 1 voltage is out of predetermined range, DTC P0152 will set.

For duplication of DTC, ensure

DTCs P0101, P0102, P0103, P0112, P0113, P0117, P0118, P0121, P0122, P0123, P0125, P0200, P0335, P0336, P0351-P0358, and P1258 are not set.
AIR, EGR and catalyst diagnostics are not active.
Ignition voltage is greater than 9 volts.
Fuel system is operating in closed loop.
Fuel trim learn is enabled.
TP angle is between 2 and 70 percent.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-introduction__on-board-diagnostic-obd-system-check) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Start engine and allow it to reach normal operating temperature. Using scan tool, monitor HO2S 1 voltage. If voltage is greater than 775 mV go to step 4 . If voltage is not greater than 775 mV, go to next step.
Turn engine off. Turn ignition on. Using scan tool, review FREEZE FRAME and/or FAILURE RECORDS data for this DTC. Turn ignition off for 15 seconds. Start engine and allow it to reach operating temperature. Operate vehicle under conditions required to set DTC. Using scan tool, read SPECIFIC DTC. If scan tool displays DTC P0132 FAILED THIS IGN, go to next step. If scan tool does not display DTC P0132 FAILED THIS IGN, see «DIAGNOSTIC AIDS»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p0135-p0204) .
Turn ignition off. Monitor HO2S 1 voltage on scan tool. If voltage is greater than 775 mV, go to next step. If voltage is not greater than 775 mV, see «DIAGNOSTIC AIDS»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p0135-p0204) .
While monitoring HO2S 1 voltage, remove HO2S 1 heater fuse (15-amp) located in underhood electrical center. If voltage drops to 350-550 mV, go to next step. If voltage does not drop to 350-550 mV, go to step 7 .
Reinstall fuse. Disconnect HO2S 1. Using a jumper wire, jumper HO2S 1 low circuit (PCM side) to ground. Monitor HO2S 1 voltage on scan tool. If voltage is 350-550 mV, go to step 10 . If voltage is not 350-550 mV, go to step 8 .
Turn ignition off. Disconnect PCM harness connector C1. Disconnect HO2S 1. Turn ignition on. Check for voltage on HO2S 1 signal circuit at PCM harness connector. If voltage is present, go to next step. If voltage is not present, go to step 9 .
Repair short to voltage in HO2S 1 signal circuit. After repairs, go to step 11 .
Replace PCM. Program replacement PCM using required equipment. After repairs, go to step 11 .
Replace HO2S 1. After repairs, go to next step.
Using scan tool, clear DTCs. Start and warm engine to normal operating temperature. Select DTC, SPECIFIC, and then enter this DTC. Operate vehicle within the conditions for setting this DTC. If scan tool indicates that this test ran and passed, go to next step. If scan tool does not indicate that this test ran and passed, go to step 2 .
Using scan tool, select CAPTURE INFO, REVIEW INFO. If any undiagnosed DTCs are displayed, go to applicable DTC test. If no undiagnosed DTCs are displayed, system is okay.

System will be rich if fuel pressure is too high. PCM can compensate for some increase in fuel pressure, but if pressure is too high, DTC may set. Check for rich or leaking injector. Check for fuel contaminated oil. Check for fuel saturation in EVAP canister purge. If full of fuel, check canister control and hoses. Check for leaking fuel pressure regulator diaphragm by checking vacuum line to regulator for fuel.

Check for an intermittent TP sensor output that will cause system to go rich due to false indication of moving throttle. Check for false rich indication due to silicon contamination of HO2S 1 indicated by DTC accompanied by lean driveability conditions and a powdery white deposit on sensor.

Check for internally shorted HO2S 1 as indicated by a voltage of greater than one volt on scan tool. Disconnect HO2S 1. If voltage changes from greater than one volt to about.45 volt, replace HO2S 1. DO NOT solder HO2S 1 wires.

Disconnect MAF sensor. If rich condition is corrected, check for improper installation. System will remain rich if MAF sensor is installed backwards. Replace MAF sensor if necessary.

DTC P0152: HO2S CIRCUIT-HIGH VOLTAGE-BANK 2, SENSOR 1 (5.7L "F" & "Y" BODIES)

Note. For circuit reference, see appropriate wiring diagram in WIRING DIAGRAMS article.

PCM supplies about 450 mV between HO2S 1 signal and ground circuits. HO2S 1 voltage ranges from about 1000 mV when exhaust is rich to about 10 mV when exhaust is lean. PCM monitors and stores sensor voltage information and evaluates voltage samples to determine amount of time sensor voltage is out of range. If PCM detects HO2S 1 voltage is more than predetermined voltage, DTC P0152 will set.

For duplication of DTC, ensure

DTCs P0101, P0102, P0103, P0112, P0113, P0117, P0118, P0121, P0122, P0123, P0125, P0200, P0335, P0336, P0351-P0358 or P1258 are not set.
Fuel system is operating in closed loop.
AIR, EGR and catalyst diagnostics are not active.
Ignition voltage is greater than 9 volts.
TP sensor angle is between 2 and 70 percent.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-introduction__on-board-diagnostic-obd-system-check) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Start and warm engine to normal operating temperature. Using scan tool, select ENGINE 1 DATA LIST and monitor HO2S 1 voltage, with engine speed at greater than 1200 RPM. If voltage is greater than 775 mV, go to step 4 . If voltage is not greater 775 mV, go to next step.
Turn ignition on, with engine off. Using scan tool, review FREEZE FRAME and/or FAILURE RECORDS data and note parameters. Turn ignition off for about 15 seconds. Start engine and operate vehicle within conditions required for this diagnostic to run, and as close to conditions recorded in FREEZE FRAME/FAILURE RECORDS as possible. Select DTC function, and then enter DTC P0152. If scan tool indicates that this test failed this ignition, go to next step. If scan tool does not indicate that this test failed this ignition, see «DIAGNOSTIC AIDS»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p0135-p0204) .
Turn ignition on, with engine off. Monitor HO2S 1 voltage with scan tool. If voltage is greater than 775 mV, go to next step. If voltage is not greater than 775 mV, see «DIAGNOSTIC AIDS»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p0135-p0204) .
Remove HO2S 1 heater fuse, while monitoring HO2S 1 voltage. If voltage is within range of 350-550 mV, go to next step. If voltage is not within range of 350-550 mV, go to step 7 .
Reinstall fuse. Disconnect HO2S 1 harness connector. Connect a fused jumper wire between ground and PCM connector (PCM side) HO2S 1 low circuit. If voltage is within range of 350-550 mV, go to step 10 . If voltage is not within range of 350-550 mV, go to step 8 .
Turn ignition off. Disconnect PCM harness connector C1. Disconnect HO2S 1 harness connector. Turn ignition on. Check for voltage on HO2S 1 signal circuit at PCM harness connector. If voltage is present, go to next step. If voltage is not present, go to step 9 .
Repair short to voltage in HO2S 1 signal circuit. After repairs, go to step 11 .
Replace PCM. Program replacement PCM using required equipment. After repairs, go to step 11 .
Replace HO2S 1. After repairs, go to next step.
Using scan tool, clear DTCs. Start and warm engine to normal operating temperature. Select DTC, SPECIFIC, and then enter DTC P0152. Operate vehicle within conditions for setting this DTC. If scan tool indicates that this test ran and passed, go to next step. If scan tool does not indicate that this test ran and passed, go to step 2 .
Using scan tool, select CAPTURE INFO, REVIEW INFO function. If any undiagnosed DTCs are displayed, go to applicable DTC test. If no undiagnosed DTCs are displayed, system is okay.

Check EVAP system for fuel saturation. Check MAF sensor. Disconnect MAF harness connector and see if rich condition is corrected. If rich condition is corrected, check for incorrectly installed MAF sensor or faulty MAF sensor. Check HO2S 1 wires for breaks or contamination. Check TP sensor. See appropriate SYSTEM & COMPONENT TESTING article.

DTC P0153: HO2S CIRCUIT-SLOW RESPONSE-BANK 2, SENSOR 1 (3.8L "F" BODY)

Note. For circuit reference, see appropriate wiring diagram in WIRING DIAGRAMS article.

PCM provides about 0.45 volt reference to Heated Oxygen Sensor 1 (HO2S 1). Sensor signal voltage varies from about one volt when exhaust is rich to about 0.1 volt when exhaust is lean. PCM counts number of times a rich-to-lean and lean-to-rich response is indicated and adds amount of time it takes to complete all transitions. PCM uses this information to determine average time for each transition. If average response time is slow, DTC P0153 will set.

For duplication of DTC, ensure

No misfire, fuel injector circuit, fuel trim, EVAP system, CKP, MAF, TP, IAT or MAP sensor DTCs are set.
Engine has been running in closed loop fuel control mode for at least 2 minutes.
Engine speed is 1000-3000 RPM.
ECT is greater than 167°F (75°C).
MAF is 15-29 grams per second.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-introduction__on-board-diagnostic-obd-system-check) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
If any other HO2S DTCs (except P0133, P1133, P1134, P1153, and/or P1154) are set, diagnose affected DTCs. Start engine and allow it to reach operating temperature. Operate vehicle within conditions required to set DTC. Using scan tool, read SPECIFIC DTC. If scan tool displays DTC P0153 FAILED THIS IGN, go to next step. If scan tool does not display DTC P0153 FAILED THIS IGN, see «DIAGNOSTIC AIDS»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p0135-p0204) .
If scan tool also displays DTC P0153, P1133, P1134, P1153, and or P1154, FAILED THIS IGN, go to step 8 . If scan tool does not display these DTCs, go to next step.
Visually inspect exhaust system for leaks near HO2S 1. If leaks are found, repair as necessary and go to step 2 . If no leaks are found, go to next step.
Visually inspect HO2S 1 for secure installation or corrosion on terminals. Check terminal tension at HO2S 1 and PCM. Check for damaged wiring. If a problem is found, go to step 9 . If no problem is found, go to next step.
Disconnect HO2S 1 harness connector. Connect a jumper wire between HO2S 1 harness connector low circuit and chassis ground. Using scan tool, read HO2S 1 voltage. If voltage is about 0.45 volt, go to next step. If voltage is not as specified, go to step 10 .
Connect a jumper wire between ground and HO2S 1 harness connector signal and low circuits. If voltage is less than 0.3 volt, go to step 12 . If voltage is not less than 0.3 volt, go to step 11 .
Repair condition causing fuel, sealant, oil or coolant contamination. Replace affected HO2S. After repairs, go to step 13 .
Repair condition as necessary. After repairs, go to step 13 .
Repair open HO2S 1 low circuit or HO2S 1 signal circuit shorted to ground. After repairs, go to step 13 .
Repair open HO2S 1 signal circuit or faulty PCM connections as necessary. After repairs, go to step 13 .
Replace HO2S 1. After repairs, go to next step.
Using scan tool, read and record FAILURE RECORDS data, and clear DTCs. Operate vehicle within conditions noted in FAILURE RECORDS data. Using scan tool, select SPECIFIC DTC INFO for DTC P0153. If scan tool displays DTC P0153 FAILED THIS IGN, go to step 2 . If scan tool does not display DTC P0153 FAILED THIS IGN, system is okay.

DTC P0153: HO2S CIRCUIT-SLOW RESPONSE-BANK 2, SENSOR 1 (4.0L "G" BODY & 4.6L "E" & "K" BODIES)

Note. For circuit reference, see appropriate wiring diagram in WIRING DIAGRAMS article.

PCM provides a.45 volt reference signal to the HO2S 1 through the Bank 2 high signal circuit. When HO2S 1 is cold, less than 392°F (200°C), the sensor signal voltage will be about.45 volt and PCM will keep the system in "open loop". When HO2S 1 is warm, sensor will swing from rich to lean rapidly, at least one switch every 2 seconds, if PCM is in good control of air/fuel mixture. If oxygen sensor is slow to respond to changes on exhaust oxygen content, DTC P0153 will set.

For duplication of DTC, ensure DTCs P0117, P0118, P0121, P0122, P0123, P0155 and P1153 are not set, this test was not completed this ignition cycle, low coolant level condition is not present, and ignition voltage is 9-16 volts.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-introduction__on-board-diagnostic-obd-system-check) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
If you are referred here from another DTC, go to step 4 . If not, go to next step.
If any other DTCs are present, diagnose affected DTCs first. If no other DTCs are present, go to next step.
Start and warm engine until coolant temperature reaches 185°F (85°C) or greater. Using scan tool, note bank 2 sensor 1 voltage display. Increase engine speed to 1200-2000 RPM for about 2 minutes. After 2 minutes, HO2S 1 voltage should swing rapidly within a range of 0.3-0.6 volt. If voltage is within range, go to next step. If voltage reading is not within range, go to step 6 .
With engine running at 1200-2000 RPM, note LOOP STATUS on scan tool. If scan tool indicates "closed loop", go to step 10 . If scan tool does not indicate "closed loop", go to step 9 .
If HO2S 1 voltage remains at.3-.6 volt range longer than the time is swings out of this range, go to step 9 . If HO2S 1 voltage is not as specified, go to next step.
Check terminal contact for HO2S 1 high signal and low circuits at PCM connector C2. Repair as necessary. If terminal contacts are okay, go to next step.
Check terminal contact at HO2S 1. Repair as necessary. If terminal contact is okay, go to next step.
Replace HO2S 1. Check for possible sensor contamination such as, leaded fuel, incorrect gasket sealer or over rich operation.
Check for possible cause of extended rich or lean operation. Repair as necessary.

DO NOT solder oxygen sensor wires.

DTC P0153: HO2S CIRCUIT-SLOW RESPONSE-BANK 2, SENSOR 1 (4.3L, 5.0L, 5.7L & 7.4L "C", "G", "K", "L", "M", "P", "S" & "T" SERIES)

Note. For circuit reference, see appropriate wiring diagram in WIRING DIAGRAMS article.

VCM supplies a voltage of about.45 volt between HO2S 1 signal and HO2S 1 ground circuits. HO2S 1 varies voltage from about one volt with rich exhaust to.1 volt with lean exhaust. VCM monitors activity for 100 seconds after closed loop. During monitored period, VCM counts how often HO2S 1 switches between rich and lean. VCM determines average switching time. If average switching time is too slow, DTC P0153 will set.

HO2S 1 produces no voltage and acts as an open circuit when temperature is less than 600°F (316°C). HO2S 1 heater provides for faster sensor warm-up allowing sensor to become active in a shorter period of time and remain active during long extended idle. DTC determines if HO2S 1 is operating properly by checking response time.

For duplication of DTC, ensure

No active EVAP system, misfire, ECT, IAT, MAF, MAP or TP sensor DTCs are set.
No intrusive tests are in progress.
No device controls are active.
System voltage is greater than 9 volts.
DTCs P0131, P0132, P0134, P0135, P0151, P0152, P0154 and P0155 are not set.
System is in closed loop.
Engine coolant temperature is greater than 135°F (57°C).
Engine is running.
MAF is 15-55 gm/s.
Engine speed is 1100-3000 RPM.
EVAP canister purge is enabled.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-introduction__on-board-diagnostic-obd-system-check) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Check if any other HO2S DTCs are set. If any other HO2S DTCs are set, go to step 4 . If no other HO2S DTCs are set, go to next step.
Check if any powertrain DTCs are set. If any powertrain DTCs are set, go to applicable DTC test. If no powertrain DTCs are set, go to step 5 .
HO2S 1 is contaminated. Repair cause of contamination and replace affected HO2S. After repairs, go to step 18 .
Using scan tool, store DTC information from VCM, and then clear DTCs. Reset fuel trim values. Start engine and allow it to reach normal operating temperature. Operate vehicle under conditions required to set DTC. If scan tool indicates this test failed this ignition, go to step 7 . If scan tool does not indicate this test failed this ignition, go to step 7 .
Condition required to set DTC is not present at this time. Check for exhaust leaks, intermittent HO2S 1 circuit faults or any conditions that may cause HO2S 1 contamination. Repair as necessary. After repairs, go to step 18 . If no problems are found, see «DIAGNOSTIC AIDS»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p0135-p0204) .
Check for exhaust leaks between engine and HO2S 1. Check for poor connections at HO2S 1 and VCM harness connectors. Repair as necessary. After repairs, go to step 18 . If no problems are found, go to next step.
Turn ignition off. Disconnect HO2S 1 harness connector. Using a jumper wire, jumper HO2S 1 low circuit (engine harness side) to ground. Turn ignition on, with engine off. Monitor HO2S 1 voltage with scan tool. If voltage is 351-551 mV, go to next step. If voltage is not 351-551 mV, go to step 13 .
Using a jumper wire, jumper HO2S 1 high signal circuit (engine harness side) to ground. Monitor HO2S 1 voltage with scan tool. If voltage is less than 20 mV, go to next step. If voltage is not less than 20 mV, go to step 14 .
Remove jumper wire from HO2S 1 low circuit. Using a test light connected to ground, probe HO2S 1 heater ignition feed circuit (engine harness side). If test light illuminates, go to next step. If test light does not illuminate, go to step 15 .
Connect test light between HO2S 1 heater ignition feed and ground circuits (engine harness side).
Check for any conditions that may cause HO2S contamination. Repair as necessary. After repairs, go to step 17 .
Repair short between HO2S 1 high signal and low circuits, or short between HO2S 1 high signal circuit and ignition voltage source.
Check HO2S 1 high signal and low circuits for an open or high resistance. Repair as necessary. After repairs, go to step 18 .
Repair HO2S 1 heater ignition feed circuit. After repairs, go to step 18 .
Repair HO2S 1 heater ground circuit. After repairs, go to step 18 .
Replace HO2S 1. After repairs, go to next step.
Using scan tool, reset fuel trim values. Start and warm engine to normal operating temperature. Select DTC, SPECIFIC, and then enter this DTC. Operate vehicle within the conditions for setting this DTC. If scan tool indicates that this test ran and passed, system is okay. If scan tool does not indicate that this test ran and passed, go to step 2 .

Check HO2S 1 heater operation. DO NOT solder HO2S 1 wires. Check for proper terminal connections.

DTC P0153: HO2S CIRCUIT-SLOW RESPONSE-BANK 2, SENSOR 1 (4.8L, 5.3L & 6.0L "C" & "K" SERIES & 5.7L "F" & "Y" BODIES)

Note. For circuit reference, see appropriate wiring diagram in WIRING DIAGRAMS article.

PCM continuously monitors HO2S 1 activity for 100 seconds. During this period, PCM counts number of times HO2S 1 responds from rich to lean and from lean to rich, and adds amount of time it took to complete transition. With this information, an average time for all transitions can be determined. If average response time is too slow, DTC P0153 will set.

A lean to rich transition is determined when HO2S 1 voltage changes from less than 300 mV to greater than 600 mV. A rich to lean transition is determined when HO2S 1 voltage changes from greater than 600 mV to less than 300 mV. A sensor that responds too slowly is most likely defective and should be replaced.

For duplication of DTC, ensure

DTCs P0101, P0102, P0103, P0112, P0113, P0117, P0118, P0121, P0122, P0123, P0125, P0200, P0335, P0336, P0351-P0358, P1120, P1220, P1221 or P1258 are not set.
Engine coolant temperature is greater than 122°F (50°C).
Ignition voltage is greater than 9 volts.
AIR, EGR and catalyst diagnostics are not active.
Fuel system is operating in closed loop.
Engine speed is 1000-2300 RPM.
Engine airflow is 20-50 gm/s.
EVAP canister purge duty cycle is greater than zero percent.
Engine has been operating for more than 2 minutes.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-introduction__on-board-diagnostic-obd-system-check) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Start and warm engine to normal operating temperature. Using scan tool, select ENGINE 1 DATA LIST and operate vehicle within parameters when DTC was set. Using scan tool, select DTC INFO and monitor FAIL THIS IGN data. If scan tool indicates that DTC P0153 test failed, go to next step. If scan tool does not indicate that this test failed, see «DIAGNOSTIC AIDS»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p0135-p0204) .
If scan tool also indicates that DTC P0133 test failed, go to step 8 . If scan tool does not indicate that DTC P0133 test failed, go to next step.
Check exhaust system for leaks. Repair as necessary. After repairs, go to step 14 . If exhaust is okay, go to next step.
Ensure HO2S 1 is securely installed. Check for corroded terminals or damaged wiring. Repair as necessary. After repairs, go to step 14 . If wiring and terminals are okay, go to next step.
Disconnect HO2S 1. Connect a fused jumper wire between ground and HO2S 1 low circuit (PCM side). Using scan tool, select ENGINE 1 DATA LIST and monitor HO2S 1 voltage. If voltage is 350-550 mV, go to next step. If voltage is not 350-550 mV, go to step 10 .
Connect a fused jumper wire between ground and HO2S 1 high signal and low circuits (PCM side). Using scan tool, monitor voltage. If voltage is less than 200 mV, go to step 13 . If voltage is not less than 200 mV, go to step 9 .
Replace HO2S 1. Determine cause of sensor contamination, otherwise new sensor will be damaged. After repairs, go to step 14 .
Remove jumper wire from HO2S 1 low circuit. Measure voltage between battery ground and HO2S 1 low circuit. If voltage is near 5 volts, go to step 12 . If voltage is not near 5 volts, go to step 11 .
Repair HO2S 1 high signal circuit for short to ground or short to voltage. After repairs, go to step 14 .
Repair open in HO2S 1 low circuit or faulty PCM harness connections. After repairs, go to step 14 .
Repair open in HO2S 1 high signal circuit or faulty PCM harness connections. After repairs, go to step 14 .
Replace HO2S 1. After repairs, go to next step.
Using scan tool, clear DTCs. Start and warm engine to normal operating temperature. Select DTC, SPECIFIC, and then enter DTC P0153. Operate vehicle within conditions for setting this DTC. If scan tool indicates that this test ran and passed, go to next step. If scan tool does not indicate that this test ran and passed, go to step 2 .
Using scan tool, select CAPTURE INFO, REVIEW INFO function. If any undiagnosed DTCs are displayed, go to applicable DTC test. If no undiagnosed DTCs are displayed, system is okay.

A malfunction in HO2S 1 heater circuit will set DTC. Check circuit for intermittent open or faulty connectors. Oxygen supply inside HO2S 1 is provided through HO2S 1 wires.

Use of FREEZE FRAME and/or FAILURE RECORDS mode will aid in locating intermittent condition. If DTC cannot be duplicated, information in data can be useful in determining how many miles since DTC set. This mode can also be used to determine how many ignition cycles diagnostic reported a pass and/or fail condition. Operating vehicle within FREEZE FRAME conditions (RPM, load, vehicle speed, temperature, etc.) will isolate when DTC failed.

DTC P0154: HO2S CIRCUIT-INSUFFICIENT ACTIVITY-BANK 2, SENSOR 1 (3.0L "V" BODY)

Note. For circuit reference, see appropriate wiring diagram in WIRING DIAGRAMS article.

For duplication of DTC, ensure engine is running, event counter value is greater than 20, and HO2S maximum value has been exceeded.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-introduction__on-board-diagnostic-obd-system-check) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Check for exhaust leaks between bank 1 HO2S 1 and HO2S 2. If a leak is found, go to step 6 . If no leaks are found, go to next step.
Turn ignition off. Disconnect HO2S 1. Check connectors for contamination. If a problem is found, go to step 7 . If connectors are okay, go to next step.
Disconnect ECM harness connector C2. Check circuits between HO2S 1 harness connector and ECM harness connector for an open, short together, or short to ground. If a problem is found, go to step 8 . If circuits are okay, go to next step.
Replace HO2S 1. After repairs, go to step 9 .
Repair exhaust leak as necessary. After repairs, go to step 9 .
Repair connections as necessary. After repairs, go to step 9 .
Repair affected circuit as necessary. After repairs, go to next step.
Using scan tool, clear DTCs. Start engine and allow it to idle. Ensure engine is at normal operating temperature. Operate vehicle within conditions required for setting this DTC. Select SPECIFIC DTC function, and then enter DTC P0154. If scan tool indicates this test ran and passed, go to next step. If scan tool does not indicate this test ran and passed, go to step 2 .
If any other DTCs are set, diagnose DTCs as necessary. If no other DTCs are set, system is okay.

HO2S 1 pigtail or harness may be mispositioned and contacting exhaust system. Inspect harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, poor terminal-to-wire connection, corrosion or water intrusion.

DTC P0154: HO2S CIRCUIT-INSUFFICIENT ACTIVITY-BANK 2, SENSOR 1 (3.8L "F" BODY)

Note. For circuit reference, see appropriate wiring diagram in WIRING DIAGRAMS article.

For duplication of DTC, ensure no misfire, fuel injector circuit, fuel trim, EVAP system, EGR, CKP, MAF, TP, IAT, MAP or ECT sensor DTCs are set, system voltage is greater than 9 volts, and engine has been running for at least 4 minutes.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-introduction__on-board-diagnostic-obd-system-check) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Start and warm engine to normal operating temperature. Place gear selector in Park or Neutral, and apply parking brake. Increase engine speed to greater than 1200 RPM for 2 minutes. Using scan tool, read HO2S 1 voltage. If voltage is outside of 0.4-0.5 volt range, go to next step. If voltage is within 0.4-0.5 volt range, go to step 4 .
Turn engine off. Turn ignition on, engine off. Using scan tool, read and record FAILURE RECORDS data. Operate vehicle within conditions noted in FAILURE RECORDS data. Using scan tool, read SPECIFIC DTC. If scan tool displays DTC P0154 FAILED THIS IGN, go to next step. If scan tool does not display DTC P0154 FAILED THIS IGN, see «DIAGNOSTIC AIDS»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p0135-p0204) .
Connect jumper wires between chassis ground and HO2S 1 harness connector signal and low circuits. If voltage is less than 0.15 volt, go to step 8 . If voltage is not less than 0.15 volt, go to next step.
Remove jumper wire from HO2S 1 signal circuit. Using DVOM, measure voltage between HO2S 1 harness connector signal and heater ground circuits. If voltage is about 0.45 volt, go to next step. If voltage is not as specified, go to step 7 .
Turn ignition off. Disconnect PCM harness connectors. Measure resistance of HO2S 1 harness connector ground circuit. If resistance is greater than 5 ohms, repair open or faulty connection as necessary. After repairs, go to step 13 . If resistance is not greater than 5 ohms, go to step 9 .
Turn ignition off. Disconnect PCM harness connectors. Measure resistance of HO2S 1 harness connector signal circuit, and then low circuit. If resistance is greater than 5 ohms on either circuit, repair open or faulty connection as necessary. After repairs, go to step 13 . If resistance is 5 ohms or less on both circuits, go to step 10 .
Check for faulty connection at HO2S 1. Repair as necessary. After repairs, go to step 13 . If connection is okay, go to step 11 .
Check HO2S 1 low circuit for faulty connection at PCM. Repair as necessary. After repairs, go to step 13 . If connection is okay, go to step 12 .
Check HO2S 1 signal circuit for faulty connection at PCM. Repair as necessary. After repairs, go to step 13 . If connection is okay, go to step 12 .
Replace HO2S 1. After repairs, go to step 13 .
Replace PCM. Program replacement PCM using required equipment. After repairs, go to next step.
Using scan tool, read and record FAILURE RECORDS data, and clear DTCs. Operate vehicle within conditions noted in FAILURE RECORDS data. Using scan tool, select SPECIFIC DTC INFO for DTC P0154. If scan tool displays DTC P0154 FAILED THIS IGN, go to step 2 . If scan tool does not display DTC P0154 FAILED THIS IGN, system is okay.

DTC P0154: HO2S CIRCUIT-INSUFFICIENT ACTIVITY-BANK 2, SENSOR 1 (4.0L "G" BODY & 4.6L "E" & "K" BODIES)

Note. For circuit reference, see appropriate wiring diagram in WIRING DIAGRAMS article.

PCM provides a.45 volt reference signal to the HO2S 1 through the Bank 2 high signal circuit. When HO2S 1 reaches operating temperature, it will generate a counter voltage that will vary based on the amount of oxygen in the exhaust. A lean exhaust will generate a low voltage and cause the reference voltage (.45 volt) to drop lower. A rich exhaust will generate a high voltage and cause the reference voltage to increase. If sensor cannot respond under the test conditions and generate a voltage greater than.61 volt or less than.31 volt, DTC P0154 will set.

For duplication of DTC, ensure DTCs P0117, P0118, P0121, P0122 and P0123 are not set, coolant temperature is 163°F (72.5°C) or greater, TP sensor angle is 1.0-81.6 degrees, calculated throttle position switch is open, and engine speed is 800 RPM or greater.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-introduction__on-board-diagnostic-obd-system-check) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Start and warm engine until coolant temperature reaches about 185°F (85°C) or greater. Using scan tool, monitor bank 2 sensor 1 voltage display for 30 seconds. If voltage remains.3-.6 volt, go to next step. If voltage does not remain.3-.6 volt, go to step 6 .
Turn ignition off. Disconnect front HO2S 1 harness connector. Start engine. Using DVOM, measure voltage between HO2S 1 harness connector terminals "A" and "B". If voltage remains.3-.6 volt, diagnose using DTC P0153 test. If voltage does not remain.3-.6 volt, go to next step.
Store fluid life index as indicated on scan tool. Turn ignition off for 30 seconds, and then disconnect PCM harness connector C2. Using DVOM, measure resistance of HO2S 1 high signal circuit between PCM and HO2S 1 harness connectors. If resistance is 5 ohms or less, go to next step. If resistance is not 5 ohms or less, go to step 9 .
Measure resistance of HO2S 1 low circuit between PCM and HO2S 1 harness connectors. If resistance is 5 ohms or less, go to next step. If resistance is not 5 ohms or less, go step 10 .
Turn ignition on, with engine off. Measure voltage between HO2S 1 harness connector terminals "C" and "D". If voltage is greater than 10.5 volts, go to next step. If voltage is not greater than 10.5 volts, go to step 8 .
Using jumper wire, jumper HO2S 1 pigtail terminal "D" to HO2S 1 harness connector terminal "D". Set DVOM to amp scale. Install DVOM in series between HO2S 1 pigtail terminal "C" and HO2S 1 harness connector terminal "C". If reading is 0.9-1.5 amps, go to step 14 . If reading is not as specified, go to step 13 .
Measure voltage between HO2S 1 harness connector terminal "D" to ground. If voltage is 10.5 volts or greater, go to step 11 . If voltage is not 10.5 volts or greater, go to step 12 .
Repair open in HO2S 1 high signal circuit.
Repair open in HO2S 1 low circuit.
Repair open in HO2S 1 ground circuit.
Repair open or short to ground in HO2S 1 ignition feed circuit.
Replace HO2S 1.
Check terminal contacts at PCM harness connector C2. Repair as necessary. If terminal contacts are okay, go to next step.
Replace PCM. Program replacement PCM using required equipment.

DTC P0154: HO2S CIRCUIT-INSUFFICIENT ACTIVITY-BANK 2, SENSOR 1 (4.3L "L" & "M" SERIES)

Note. For circuit reference, see appropriate wiring diagram in WIRING DIAGRAMS article.

VCM provides about 0.45 volt reference to Heated Oxygen Sensor 1 (HO2S 1). HO2S 1 signal voltage varies from about one volt when exhaust is rich to about 0.1 volt when exhaust is lean. VCM reads and stores sensor voltage information and evaluates the voltage samples to determine amount of time sensor voltage is out of range. If HO2S 1 voltage is out of predetermined range, DTC P0154 will set.

For duplication of DTC, ensure

No misfire, EVAP system, ECT, EGR, IAT, MAF, MAP or TP sensor DTCs are set.
No intrusive tests are in progress.
No device controls are active.
System voltage is 11.7-18 volts.
Engine has been running for at least 2 minutes.
Deceleration Fuel Cut-Off (DFCO) mode is not active.
System is in closed loop.
Engine coolant temperature is greater than 136°F (58°C).
MAF is greater than 13 gm/s.
DTC P0155 is not active.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-introduction__on-board-diagnostic-obd-system-check) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Using scan tool, record DTC information from VCM. Clear DTCs and reset fuel trim values. Start and warm engine to normal operating temperature. Monitor HO2S 1 voltage with scan tool. If voltage is fixed at 300-600 mV, go to step 4 . If voltage is not fixed at 300-600 mV, go to next step.
Condition required to set DTC is not present at this time. Check for defective HO2S 1, exhaust leaks or intermittent HO2S 1 circuit faults. Repair as necessary. After repairs, go to step 15 . If no problems are found, see «DIAGNOSTIC AIDS»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p0135-p0204) .
Turn ignition off. Disconnect HO2S 1 harness connector. Using jumper wires, jumper HO2S 1 high signal and low circuits to ground. Turn ignition on, with engine off. Monitor HO2S 1 voltage with scan tool. If voltage is less than 20 mV, go to step 7 . If voltage is not less than 20 mV, go to next step.
Turn ignition off. Remove jumper wires. Disconnect VCM harness connector containing HO2S 1 high signal and low circuits. Measure resistance of HO2S 1 high signal and low circuits between VCM and HO2S 1 harness connectors. If resistance of each circuit is less than 5 ohms, go to next step. If resistance of either circuit is 5 ohms or greater, go to step 11 .
Check for faulty VCM harness connections. Repair as necessary. After repairs, go to step 15 . If connections are okay, go to step 14 .
Remove jumper wires. Ensure ignition is on. Connect test light between heater ignition feed and heater ground circuits at HO2S 1 harness connector. If test light illuminates, go to step 9 . If test light does not illuminate, go to next step.
Repair HO2S 1 heater ignition feed or heater ground circuit. After repairs, go to step 15 .
Check for exhaust leaks upstream of HO2S 1. Repair as necessary. After repairs, go to step 15 . If no leaks are found, go to next step.
Check for any condition that may cause skewed reference voltage (i.e., open or poor connections in HO2S 1 circuits, faulty VCM grounds, or ungrounded exhaust system). Repair as necessary. After repairs, go to step 12 .
Repair circuit that measured high resistance. After repairs, go to step 15 .
Remove HO2S 1. Clean threads, apply anti-seize compound and reinstall. Measure resistance between HO2S 1 low circuit and one of the VCM ground circuits at VCM harness connector. If resistance is less than 500 ohms, go to step 15 . If resistance is not less than 500 ohms, go to next step.
Replace HO2S 1. After repairs, go to step 15 .
Replace VCM. Program replacement VCM using required equipment. Perform Passlock® reprogramming and CKP system variation learn procedures. After repairs, go to next step.
Using scan tool, clear DTCs. Start engine and allow it to reach operating temperature. Using scan tool, select DTC, SPECIFIC function and enter this DTC. Operate vehicle within conditions required to set DTC. If scan tool indicates this test ran and passed, go to next step. If scan tool does not indicate this test ran and passed, go to step 2 .
Using scan tool, select CAPTURE INFO, REVIEW INFO function If any undiagnosed DTCs are displayed, go to applicable DTC test. If no undiagnosed DTCs are displayed, system is okay.

Check for faulty connections or damaged harness. Check for faulty HO2S 1 heater. Observe scan tool while moving all related harnesses and connectors. A change in scan tool display indicates fault location.

DTC P0154: HO2S CIRCUIT-INSUFFICIENT ACTIVITY-BANK 2, SENSOR 1 (4.3L, 5.0L, 5.7L & 7.4L "C", "G", "K", "P", "S" & "T" SERIES)

Note. For circuit reference, see appropriate wiring diagram in WIRING DIAGRAMS article.

VCM supplies a voltage of about.45 volt between HO2S 1 signal and HO2S 1 ground circuits. HO2S 1 varies voltage from about one volt with rich exhaust to 0.1 volt with lean exhaust. HO2S 1 produces no voltage and acts as an open circuit when temperature is less than 600°F (316°C). An open sensor circuit or a cold sensor causes open loop operation.

HO2S 1 heater provides for faster sensor warm-up allowing sensor to become active in a shorter period of time and remain active during long extended idle. DTC determines if HO2S 1 or HO2S 1 circuit is open.

For duplication of DTC, ensure

No misfire, EVAP system, ECT, IAT, MAF, MAP or TP sensor DTCs are set.
No intrusive tests are in progress.
No device controls are active.
System voltage is at least 9 volts.
Engine run time is at least 2 minutes.
Deceleration Fuel Cut-Off (DFCO) mode is not active.
System is in closed loop.
Engine coolant temperature is greater than 176°F (80°C).
MAF is 15 gm/s or greater.
DTCs P0147 and P0155 are not active.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-introduction__on-board-diagnostic-obd-system-check) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Using scan tool, record DTC information from VCM. Clear DTCs and reset fuel trim values. Start and warm engine to normal operating temperature. Monitor HO2S 1 voltage with scan tool. If voltage is fixed at 350-550 mV, go to step 4 . If voltage is not fixed at 350-550 mV, go to next step.
Condition required to set DTC is not present at this time. Check for defective HO2S 1, exhaust leaks or intermittent HO2S 1 circuit faults. Repair as necessary. After repairs, go to step 17 . If no problems are found, see «DIAGNOSTIC AIDS»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p0135-p0204) .
Turn ignition off. Disconnect HO2S 1 harness connector. Using jumper wires, jumper HO2S 1 high signal and low circuits to ground. Turn ignition on, with engine off. Monitor HO2S 1 voltage with scan tool. If voltage is less than 20 mV, go to step 7 . If voltage is not less than 20 mV, go to next step.
Turn ignition off. Remove jumper wires. Disconnect VCM harness connector containing HO2S 1 high signal and low circuits. Measure resistance of HO2S 1 high signal and low circuits between VCM and HO2S 1 harness connectors. If resistance of both circuits is less than 5 ohms, go to next step. If resistance of either circuit is 5 ohms or greater, go to step 9 .
Check for faulty VCM harness connections. Repair as necessary. After repairs, go to step 17 . If connections are okay, go to step 16 .
Remove jumper wires. Ensure ignition is on. Connect test light between heater ignition feed and heater ground circuits at HO2S 1 harness connector. If test light illuminates, go to next step. If test light does not illuminate, go to step 10 .
Turn ignition off. Reconnect HO2S 1 harness connector. Disconnect VCM harness connectors containing HO2S 1 low circuit and VCM ground circuits. Measure resistance between HO2S 1 low circuit and one of the VCM ground circuits at VCM harness connector. If resistance is less than 500 ohms, go to step 12 . If resistance is not less than 500 ohms, go to step 11 .
Repair circuit that measured high resistance. After repairs, go to step 17 .
Repair HO2S 1 heater ignition feed or heater ground circuit. After repairs, go to step 17 .
Repair high resistance between HO2S 1 low circuit and VCM ground circuit. After repairs, go to step 17 .
Check for exhaust leaks upstream of HO2S 1. Repair as necessary. After repairs, go to step 17 . If no leaks are found, go to next step.
Allow engine to cool completely. Measure resistance between HO2S 1 low circuit and one of the VCM ground circuits at VCM harness connector. If resistance is less than 500 ohms, go to step 15 . If resistance is not less than 500 ohms, go to next step.
Remove HO2S 1. Clean threads, apply anti-seize compound and reinstall. Measure resistance between HO2S 1 low circuit and one of the VCM ground circuits at VCM harness connector. If resistance is less than 500 ohms, go to step 17 . If resistance is not less than 500 ohms, go to next step.
Replace HO2S 1. After repairs, go to step 17 .
Replace VCM. Program replacement VCM using required equipment. Perform Passlock® reprogramming and CKP system variation learn procedures. After repairs, go to next step.
Using scan tool, clear DTCs. Start and warm engine to normal operating temperature. Select DTC, SPECIFIC, and then enter this DTC. Operate vehicle within the conditions for setting this DTC. If scan tool indicates that this test ran and passed, go to next step. If scan tool does not indicate that this test ran and passed, go to step 2 .
Using scan tool, select CAPTURE INFO, REVIEW INFO. If any undiagnosed DTCs are displayed, go to applicable DTC test. If no undiagnosed DTCs are displayed, system is okay.

With ignition on and engine off, HO2S 1 voltage on scan tool should gradually decrease to less than.15 volt indicating heater is operating properly. If voltage does not decrease as specified, disconnect HO2S 1 harness connector and connect a test light between HO2S 1 harness connector terminals "C" and "D" (engine harness side). If test light illuminates, replace HO2S 1. If test light does not illuminate, repair open in HO2S 1 heater ground circuit or HO2S 1 ignition feed circuit.

Using scan tool, monitor signal voltage while wiggling HO2S 1 related connectors and wiring harness with a warm engine running at part throttle in closed loop. If a failure is induced, signal voltage will change from normal fluctuating voltage of greater than.6 volt and less than.3 volt, to a fixed voltage of about.45 volt. A change in voltage will assist in isolating location of fault. DO NOT solder HO2S 1 wires.

DTC P0154: HO2S CIRCUIT-INSUFFICIENT ACTIVITY-BANK 2, SENSOR 1 (4.8L, 5.3L & 6.0L "C" & "K" SERIES & 5.7L "F" & "Y" BODIES)

Note. For circuit reference, see appropriate wiring diagram in WIRING DIAGRAMS article.

Powertrain Control Module (PCM) supplies about.45 volt to Heated Oxygen Sensor 1 (HO2S 1). The HO2S 1 generates a voltage that varies from about one volt when exhaust is rich to about 0.1 volt when exhaust is lean. PCM monitors and stores sensor voltage information and evaluates the voltage samples to determine amount of time sensor voltage is out of range. If PCM detects HO2S 1 voltage remains at or near.45 volt for an extended period of time, DTC P0154 will set.

For duplication of DTC, ensure

DTCs P0101, P0102, P0103, P0112, P0113, P0117, P0118, P0121, P0122, P0123, P0125, P0200, P0335, P0336, P0351-P0358 and P1258 are not set.
Ignition voltage is greater than 9 volts.
AIR, EGR and catalyst diagnostics are not active.
Fuel system is operating in closed loop.
Engine run time is greater than 70 seconds.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-introduction__on-board-diagnostic-obd-system-check) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Start and warm engine to normal operating temperature. Increase engine speed to 1200 RPM for 2 minutes. Using scan tool, select ENGINE 1 and note HO2S 1 voltage. If voltage varies from less than 350 mV to greater than 550 mV, go to next step. If voltage does not vary as specified, go to step 4 .
Turn ignition on. Using scan tool, read and record FAILURE RECORDS data. Turn ignition off for 15 seconds. Start engine and operate vehicle within conditions noted in FAILURE RECORDS data. Using scan tool, read SPECIFIC DTC. If scan tool displays DTC P0154 FAILED THIS IGN, go to next step. If scan tool does not display DTC P0154 FAILED THIS IGN, see «DIAGNOSTIC AIDS»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p0135-p0204) .
Turn ignition on, with engine off. Disconnect HO2S 1. Using jumper wires, jumper HO2S 1 high and low signal circuits to ground. Monitor HO2S 1 voltage with scan tool. If voltage is less than 200 mV, go to step 8 . If voltage is not less than 200 mV, go to next step.
Remove jumper wire from HO2S 1 low signal circuit. Measure voltage between ground and low signal circuit at HO2S 1 harness connector. If voltage is about 5 volts, go to next step. If voltage is not about 5 volts, go to step 7 .
Turn ignition off. Disconnect PCM harness connector C1. Check for continuity in HO2S 1 high signal circuit between HO2S 1 and PCM harness connectors. Repair open circuit if continuity is not present. After repairs, go to step 12 . If circuit is okay, go to step 10 .
Turn ignition off. Disconnect PCM harness connector C1. Check for continuity in HO2S 1 low signal circuit between HO2S 1 and PCM harness connectors. Repair open circuit if continuity is not present. After repairs, go to step 12 . If circuit is okay, go to step 10 .
Check HO2S 1 circuits for poor connections at HO2S 1 harness connector. Repair as necessary. After repairs, go to step 12 . If connections are okay, go to next step.
Replace HO2S 1. After repairs, go to step 12 .
Check HO2S 1 circuits for poor connections at PCM. Repair as necessary. After repairs, go to step 12 . If connections are okay, go to next step.
Replace PCM. Program replacement PCM using required equipment. After repairs, go to next step.
Using scan tool, clear DTCs. Start engine and operate vehicle under conditions required to set this DTC. If scan tool indicates this test ran and passed, go to next step. If scan tool does not indicate this test ran and passed, go to step 2 .
Using scan tool, select CAPTURE INFO, REVIEW INFO function. If any undiagnosed DTCs are displayed, go to applicable DTC test. If no undiagnosed DTCs are displayed, system is okay.

HO2S 1 requires an outside source of air for proper operation. Air is supplied through HO2S wiring. Check wires and connections for breaks or contamination. DO NOT solder HO2S wiring. Solder will obstruct air path.

DTC P0155: HO2S HEATER CIRCUIT-BANK 2, SENSOR 1 (3.0L "V" BODY)

Note. For circuit reference, see appropriate wiring diagram in WIRING DIAGRAMS article.

For duplication of DTC, ensure battery voltage is 11-15.5 volts, heater output stage is active, and engine is running.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-introduction__on-board-diagnostic-obd-system-check) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Check for exhaust leaks between HO2S 1 and HO2S 2. If a leak is found, go to step 7 . If no leaks are found, go to next step.
Turn ignition off. Disconnect HO2S 1. Check for faulty harness connections. If connections are faulty, go to step 8 . If connections are okay, go to next step.
Turn ignition off. Measure sensor resistance between sensor housing and HO2S 1 heater control circuit. If resistance is less than 100 ohms, go to step 9 . If resistance is not less than 100 ohms, go to next step.
Disconnect ECM harness connector. Using a test light connected to battery positive, probe HO2S 1 heater control circuit at ECM harness connector. If test light illuminates, go to step 10 . If test light does not illuminate, go to next step.
Check for continuity in HO2S 1 heater control circuit between HO2S 1 and ECM. If continuity is present, see «DIAGNOSTIC AIDS»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p0135-p0204) . If continuity is not present, go to step 11 .
Repair exhaust leaks as necessary. After repairs, go to step 12 .
Repair terminals as necessary. After repairs, go to step 12 .
Replace HO2S 1. After repairs, go to step 12 .
Repair short to ground. After repairs, go to step 12 .
Repair open circuit. After repairs, go to next step.
Using scan tool, clear DTCs. Start engine and operate vehicle under conditions required to set this DTC. If scan tool indicates this test ran and passed, go to next step. If scan tool does not indicate this test ran and passed, go to step 2 .
Using scan tool, select CAPTURE INFO, REVIEW INFO function. If any undiagnosed DTCs are displayed, go to applicable DTC test. If no undiagnosed DTCs are displayed, system is okay.

DTC P0155: HO2S HEATER CIRCUIT-BANK 2, SENSOR 1 (3.8L "F" BODY)

Note. For circuit reference, see appropriate wiring diagram in WIRING DIAGRAMS article.

For duplication of DTC, ensure

No EVAP system, misfire, fuel trim, fuel injector circuit, EGR pintle position, TP, IAT, MAP, ECT, CKP, or MAF sensor DTCs are set.
Engine is running.
System voltage is 9-18 volts.
ECT and IAT is less than 95°F (35°C) at start-up.
Difference between ECT and IAT is not greater than 11°F (6°C) at start-up.
Average MAF for sample period is less than 20 gm/s.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-introduction__on-board-diagnostic-obd-system-check) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Turn ignition on, engine off. Using scan tool, read HO2S 1 voltage. If voltage is varying from less than 0.3 volt to greater than 0.6 volt, see «DIAGNOSTIC AIDS»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p0135-p0204) . If voltage is within a range of 0.3-0.6 volt, go to next step.
Inspect HO2S 1 ignition feed fuse. If fuse is open, go to step 15 . If fuse is okay, go to next step.
Turn ignition off. Raise and support vehicle. Disconnect HO2S 1 harness connector. Connect a test light between chassis ground and HO2S 1 ignition feed circuit. If test light illuminates, go to next step. If test light does not illuminate, go to step 7 .
Connect test light between HO2S 1 harness connector ignition feed and heater ground circuits. If test light illuminates, go to next step. If test light does not illuminate, go to step 8 .
Allow HO2S 1 to cool for at least 10 minutes. Using DVOM, measure resistance between ignition feed and heater ground circuits at HO2S 1. If resistance is 5-10 ohms, go to step 9 . If resistance is not as specified, go to step 14 .
Repair open HO2S 1 ignition feed circuit. After repairs, go to step 16 .
Repair open HO2S 1 heater ground circuit. After repairs, go to step 16 .
Check for faulty connection at HO2S 1. Repair as necessary. After repairs, go to step 16 . If connection is okay, go to next step.
Turn ignition off. Disconnect PCM harness connectors. Measure resistance of HO2S 1 signal and ground circuits. If resistance on either circuit is greater than 5 ohms, repair open or faulty connection as necessary. After repairs, go to step 16 . If resistance is not greater than 5 ohms, go to next step.
Check for faulty connection at HO2S 1 harness connector. Repair as necessary. After repairs, go to step 16 . If connection is okay, go to next step.
Check HO2S 1 low circuit for faulty connection at PCM. Repair as necessary. After repairs, go to step 16 . If connection is okay, go to next step.
Check HO2S 1 signal circuit for faulty connection at PCM. Repair as necessary. After repairs, go to step 16 . If connection is okay, go to next step.
Replace HO2S 1. After repairs, go to step 16 .
Locate and repair short to ground in HO2S 1 ignition feed circuit, and then replace fuse. After repairs, go to next step.
Allow engine to cool completely. Using scan tool, clear DTCs. Turn ignition on, engine off. Read HO2S 1 voltage. If voltage is greater than 0.6 volt or less than 0.3 volt, system is okay. If voltage is not as specified, go to step 2 .

DTC P0155: HO2S HEATER CIRCUIT-BANK 2, SENSOR 1 (4.0L "G" BODY & 4.6L "E" & "K" BODIES)

Note. For circuit reference, see appropriate wiring diagram in WIRING DIAGRAMS article.

This test is used to determine if the heating element in the front oxygen sensor is operating properly. The sensor acts as a battery because it creates its own voltage once it reaches operating temperature. This voltage is produced when the oxygen content in the exhaust stream is different than that in the atmosphere.

Heating element is energized through the ignition circuit when ignition is on, allowing sensor to reach operating temperature quickly. This in turn allows PCM to enter into "closed loop" quicker.

When cold, the voltage that the PCM measures on the oxygen sensor high and low input circuits is called bias voltage. If it takes too long for oxygen sensor to vary the bias voltage within a specific time since ignition was turned on, DTC P0155 will set.

For duplication of DTC, ensure DTCs P0101, P0102, P0103, P0117, P0118 and P0154 are not set, ECT dropped at least 50°F (10°C) from end of the last ignition cycle to the beginning of this ignition cycle, average HO2S 1 bias voltage is 352-546 mV, and engine did not stall during test.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-introduction__on-board-diagnostic-obd-system-check) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Turn ignition on, with engine off. Disconnect HO2S 1 harness connector. Using DVOM, measure voltage between HO2S 1 harness connector terminals "C" and "D". If voltage is 10.5 volts or greater, go to next step. If voltage is not 10.5 volts or greater, go to step 4 .
Using jumper wire, jumper HO2S 1 pigtail terminal "D" to HO2S 1 harness connector terminal "D". Set DVOM to amp scale. Install DVOM in series between HO2S 1 pigtail terminal "C" and HO2S 1 harness connector terminal "C". Turn ignition on. If reading is 0.9-1.5 amps, go to step 5 . If reading is not as specified, go to step 8 .
Measure voltage between ground and HO2S 1 harness connector terminal "D". If voltage is 10.5 volts or greater, go to step 6 . If voltage is not 10.5 volts or greater, go to step 7 .
Using scan tool, select FREEZE FRAME data and operate vehicle in the same conditions under which the DTC set. If DTC resets, diagnose using DTC P0153 test. If DTC does not reset, fault is not present at this time. See «DIAGNOSTIC AIDS»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p0135-p0204) .
Repair open in HO2S 1 ground circuit.
Repair open or short in HO2S 1 ignition feed circuit.
Replace HO2S 1.

An intermittent open in ignition or ground circuits to HO2S 1 may cause DTC P0155 to set. A malfunctioning oxygen sensor heater could also cause DTC to set. DO NOT solder oxygen sensor wires.

DTC P0155: HO2S HEATER CIRCUIT-BANK 2, SENSOR 1 (4.3L, 5.0L, 5.7L & 7.4L "C", "G", "K", "L", "M", "P", "S" & "T" SERIES)

Note. For circuit reference, see appropriate wiring diagram in WIRING DIAGRAMS article.

VCM supplies a voltage of about.45 volt between HO2S 1 signal and HO2S 1 ground circuits. HO2S 1 varies voltage from about one volt with rich exhaust to 0.1 volt with lean exhaust. HO2S 1 produces no voltage and acts as an open circuit when temperature is less than 600°F (316°C). An open sensor circuit or a cold sensor causes open loop operation.

HO2S 1 heater provides for faster sensor warm-up allowing sensor to become active in a shorter period of time and remain active during long extended idle. DTC determines if HO2S 1 heater is operating properly by monitoring amount of time necessary for HO2S 1 to become active after start-up.

For duplication of DTC, ensure

System voltage is greater than 9 volts but less than 17 volts.
MAF is less than 27 gm/s (4.3L, 5.0L and 5.7L) or less than 45 gm/s (7.4L).
Engine run time is greater than 2 seconds.
ECT and IAT is less than 91°F (33°C).
Difference between ECT and IAT is less than 41°F (5°C) on 4.3L, 5.0L and 5.7L, and less than 47°F (8°C) on 7.4L.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-introduction__on-board-diagnostic-obd-system-check) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Ensure engine and HO2S 1 are completely cool. Install scan tool. Turn ignition on, with engine off. Immediately record HO2S 1 voltage with scan tool. Continue monitoring voltage for 2 minutes. If HO2S 1 voltage gradually increases or decreases by 150 mV from recorded value, go to next step. If HO2S 1 voltage is not as specified, go to step 4 .
Condition required to set this DTC is not present at this time. Check for faulty HO2S 1 and/or intermittent HO2S 1 circuit faults. Repair as necessary. After repairs, go to step 14 . If no problem is found, see «DIAGNOSTIC AIDS»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p0135-p0204) .
Turn ignition off. Disconnect HO2S 1 harness connector. Connect test light between HO2S 1 heater ignition feed and heater ground circuits at HO2S 1 harness connector. Turn ignition on. If test light illuminates, go to next step. If test light does not illuminate, go to step 6 .
Remove test light. Using jumper wires, jumper HO2S 1 high and low signal circuits to ground. Monitor HO2S 1 voltage with scan tool. If voltage is less than 20 mV, go to step 8 . If voltage is not less than 20 mV, go to step 7 .
Using a test light connected to ground, probe HO2S 1 heater ignition feed circuit. If test light illuminates, go to step 9 . If test light does not illuminate, go to step 10 .
Turn ignition off. Remove jumper wires. Disconnect VCM harness connector containing HO2S 1 high and low signal circuits. Measure resistance of HO2S 1 high and low signal circuits between HO2S 1 and VCM. If resistance of each circuit is less than 5 ohms, go to step 12 . If resistance of either circuit is not less than 5 ohms, go to step 11 .
Replace HO2S 1. After repairs, go to step 14 .
Repair open HO2S 1 heater ground circuit. After repairs, go to step 14 .
Repair loss of voltage on HO2S 1 heater ignition feed circuit. After repairs, go to step 14 .
Repair circuit with high resistance. After repairs, go to step 14 .
Check for faulty VCM harness connections. Repair as necessary. After repairs, go to step 14 . If connections are okay, go to next step.
Replace VCM. Program replacement VCM using required equipment. Perform Passlock® reprogramming and CKP system variation learn procedures. After repairs, go to next step.
Ensure engine and HO2S 1 are completely cool. Install scan tool. Turn ignition on, with engine off. Immediately record HO2S 1 voltage with scan tool. Continue monitoring voltage for 2 minutes. If HO2S 1 voltage gradually increases or decreases by 150 mV from recorded value, go to next step. If HO2S 1 voltage is not as specified, go to step 4 .
Using scan tool, select CAPTURE INFO, REVIEW INFO. If any undiagnosed DTCs are displayed, go to applicable DTC test. If not additional DTCs are displayed, system is okay.

DTC P0155: HO2S HEATER CIRCUIT-BANK 2, SENSOR 1 (4.8L, 5.3L & 6.0L "C" & "K" SERIES & 5.7L "F" & "Y" BODIES)

Note. For circuit reference, see appropriate wiring diagram in WIRING DIAGRAMS article.

For duplication of DTC, ensure

DTCs P0101, P0102, P0103, P0112, P0113, P0117, P0118, P0121, P0122, P0123, P0125, P0200, P0335, P0336, P0351-P0358 or P1258 are not set.
IAT and ECT sensor temperatures are less than 122°F (50°C) and are within 46°F (8°C) of each other at start-up.
Ignition voltage is 10-18 volts.
AIR, EGR and catalyst diagnostics are not active.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-introduction__on-board-diagnostic-obd-system-check) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Ensure engine and HO2S 1 are completely cool. Turn ignition on. Using scan tool, monitor HO2S 1 voltage. If voltage changes from about 450 mV to less than 300 mV or greater than 700 mV, see «DIAGNOSTIC AIDS»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p0135-p0204) . If voltage does not change as specified, go to next step.
Check for open in fuse that supplies current to HO2S 1 heater circuit. If fuse is open, go to step 11 . If fuse is okay, go to next step.
Disconnect HO2S 1 harness connector. Using a test light connected to ground, probe HO2S 1 heater ignition feed circuit. If test light illuminates, go to next step. If test light does not illuminate, go to step 7 .
Connect test light between HO2S 1 heater ignition feed and heater ground circuits at HO2S 1 harness connector. If test light illuminates, go to next step. If test light does not illuminate, go to step 8 .
Measure resistance of HO2S 1 between heater ignition feed and heater ground circuits. If resistance is 3.5-14.0 ohms, go to step 9 . If resistance is not as specified, go to step 10 .
Repair open HO2S 1 heater ignition feed circuit. After repairs, go to step 12 .
Repair open HO2S 1 heater ground circuit. After repairs, go to step 12 .
Check for faulty HO2S 1 harness connections. Repair as necessary. After repairs, go to step 12 . If connections are okay, go to next step.
Replace HO2S 1. After repairs, go to step 12 .
Repair short to ground in HO2S 1 heater ignition feed circuit. Replace fuse. After repairs, go to next step.
Using scan tool, clear DTCs. Start engine and allow it to reach normal operating temperature. Operate vehicle under conditions required to set this DTC. If scan tool indicates this test ran and passed, go to next step. If scan tool does not indicate this test ran and passed, go to step 2 .
Using scan tool, select CAPTURE INFO, REVIEW INFO. If any undiagnosed DTCs are displayed, go to applicable DTC test. If not additional DTCs are displayed, system is okay.

DTC P0156: HO2S CIRCUIT-BANK 2, SENSOR 2 (3.0L "V" BODY)

Note. For circuit reference, see appropriate wiring diagram in WIRING DIAGRAMS article.

For duplication of DTC, ensure no EVAP DTCs are set, HO2S 2 is in closed loop, secondary AIR diagnostics are not running, engine has been running for more than 10 minutes, low fuel condition is not indicated, and battery voltage is greater than 11 volts.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-introduction__on-board-diagnostic-obd-system-check) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Start and warm engine to normal operating temperature. Using scan tool, monitor HO2S 2 voltage. If voltage remains less than 399 mV, go to step 4 . If voltage does not remain less than 399 mV, go to next step.
Turn ignition on, with engine off. Review FREEZE FRAME data for this DTC and note parameters. Clear DTCs. Turn ignition off for 15 seconds. Start engine and operate vehicle as close to conditions recorded in FREEZE FRAME as possible. Check for DTCs. If DTC P0156 is set, go to next step. If DTC P0156 is not set, see «DIAGNOSTIC AIDS»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p0135-p0204) .
Turn ignition on, with engine off. Disconnect HO2S 2 harness connector. Check for signs of water or corrosion. Repair as necessary. If HO2S 2 voltage on scan tool is 375-525 mV, go to step 14 . If HO2S 2 voltage on scan tool is not 375-525 mV, go to next step.
Using DVOM, measure voltage between ground and signal circuit at HO2S 2 harness connector. If voltage is 900-1100 mV, go to next step. If voltage is not 900-1100 mV, go to step 11 .
Using DVOM, measure voltage between ground and low circuit at HO2S 2 harness connector. If voltage is 700-800 mV, go to step 22 . If voltage is not 700-800 mV, go to next step.
Continue to monitor voltage from HO2S 2 low circuit between harness connector and ground. Disconnect the 3 other HO2S harness connectors. As each sensor is disconnected, recheck voltage on DVOM. If disconnecting any of the other sensors restores voltage to 700-800 mV, go to step 14 . If disconnecting the other sensors does not restore voltage to 700-800 mV, go to next step.
Leave all HO2S harness connectors disconnected. Turn ignition off. Disconnect ECM harness connectors located in engine compartment relay center. Turn ignition on. Using DVOM, measure voltage between ground and HO2S 2 low circuit at ECM harness connector. If no voltage is present, go to next step. If voltage is present, go to step 15 .
Using DVOM, check harness continuity of HO2S 2 low circuit. If continuity is present, go to next step. If continuity is not present, go to step 16 .
Using DVOM, check harness continuity between HO2S 2 low circuit and ground. If continuity is present, go to step 17 . If continuity is not present, go to step 21 .
Leave all HO2S 2 disconnected. Turn ignition off. Disconnect ECM harness connectors located in engine compartment relay center. Turn ignition on. Using DVOM, check for voltage between ground and HO2S 2 signal circuit at ECM harness connector. If any voltage is present, go to step 18 . If no voltage is present, go to next step.
Using DVOM, check harness continuity of HO2S 2 signal circuit. If continuity is present, go to next step. If continuity is not present, go to step 19 .
Using DVOM, check harness continuity between HO2S 2 signal circuit and ground. If continuity is present, go to step 20 . If continuity is not present, go to step 21 .
Replace shorted HO2S 2. After repairs, go to step 23 .
Repair short to voltage in HO2S 2 low circuit. After repairs, go to step 23 .
Repair open or high resistance in HO2S 2 low circuit. After repairs, go to step 23 .
Repair short to ground in HO2S 2 low circuit. After repairs, go to step 23 .
Repair short to voltage in HO2S 2 signal circuit. After repairs, go to step 23 .
Repair open or high resistance in HO2S 2 signal circuit. After repairs, go to step 23 .
Repair short to ground in HO2S 2 signal circuit. After repairs, go to step 23 .
Check for poor connections and terminal tension at ECM harness connector. Repair as necessary. After repairs, go to step 23 . If connections and terminals are okay, go to next step.
Replace ECM. New ECM must be programmed with theft deterrent module frequency code currently on vehicle. After repairs, go to next step.
Using scan tool, clear DTCs. Turn ignition off for 15 seconds. Start engine and operate vehicle as close to conditions recorded in FREEZE FRAME as possible. Check for DTCs. If DTC P0156 is set, go to step 2 . If DTC P0156 is not set, go to next step.
If other DTCs were present during OBD system check and have not been diagnosed, go to applicable DTC. If no other DTCs are present, system is okay.

An exhaust leak may cause outside air to be pulled into exhaust gas stream past HO2S, causing this DTC to set. Check for exhaust leaks near HO2S.

DTC P0157: HO2S CIRCUIT-LOW VOLTAGE-BANK 2, SENSOR 2 (3.0L "V" BODY)

Note. For circuit reference, see appropriate wiring diagram in WIRING DIAGRAMS article.

For duplication of DTC, ensure no DTCs are set, HO2S 2 heater is active for more than 200 seconds, and secondary AIR diagnostics are not running.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-introduction__on-board-diagnostic-obd-system-check) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Start and operate engine to normal operating temperature. Using scan tool, monitor HO2S 2 voltage. If voltage remains less than -148 mV, go to step 4 . If voltage does not remain less than -148 mV, go to next step.
Turn ignition on, with engine off. Review FREEZE FRAME data for this DTC and note parameters. Clear DTCs. Turn ignition off for 15 seconds. Start engine and operate vehicle as close to conditions recorded in FREEZE FRAME as possible. Check for DTCs. If DTC P0157 is set, go to next step. If DTC P0157 is not set, see «DIAGNOSTIC AIDS»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p0135-p0204) .
Turn ignition on, with engine off. Disconnect HO2S 2 harness connector. Check for signs of water or corrosion. Repair as necessary. If HO2S 2 voltage is 375-525 mV, go to step 14 . If HO2S voltage is not 375-525 mV, go to next step.
Using DVOM, measure voltage between ground and signal circuit at HO2S 2 harness connector. If voltage is 900-1200 mV, go to next step. If voltage is not 900-1200 mV, go to step 11 .
Using DVOM, measure voltage between ground and low circuit at HO2S 2 harness connector. If voltage is 700-800 mV, go to step 22 . If voltage is not 700-800 mV, go to next step.
Continue to monitor voltage from HO2S 2 low circuit between harness connector and ground. Disconnect the 3 other HO2S harness connectors. As each sensor is disconnected, recheck voltage on DVOM. If disconnecting the other sensors restores voltage to 700-800 mV, go to step 14 . If disconnecting the other sensors does not restore voltage to 700-800 mV, go to next step.
Leave all HO2S 2 harness connectors disconnected. Turn ignition off. Disconnect ECM harness connectors located in engine compartment relay center. Turn ignition on. Using DVOM, check for voltage between ground and HO2S 2 low circuit at ECM harness connector. If no voltage is present, go to next step. If any voltage is present, go to step 15 .
Using DVOM, check harness continuity of HO2S 2 low circuit. If continuity is present, go to next step. If continuity is not present, go to step 16 .
Using DVOM, check harness continuity between HO2S 2 low circuit and ground. If continuity is present, go to step 17 . If continuity is not present, go to step 21 .
Leave all HO2S harness connectors disconnected. Turn ignition off. Disconnect ECM harness connectors located in engine compartment relay center. Turn ignition on. Using DVOM, check for voltage between ground and HO2S 2 signal circuit at ECM harness connector. If any voltage is present, go to step 18 . If no voltage is present, go to next step.
Using DVOM, check harness continuity of HO2S 2 signal circuit. If continuity is present, go to next step. If continuity is not present, go to step 19 .
Using DVOM, check harness continuity between HO2S 2 signal circuit and ground. If continuity is present, go to step 20 . If continuity is not present, go to step 21 .
Replace shorted HO2S 2. After repairs, go to step 23 .
Repair short to voltage in HO2S 2 low circuit. After repairs, go to step 23 .
Repair open or high resistance in HO2S 2 low circuit. After repairs, go to step 23 .
Repair short to ground in HO2S 2 low circuit. After repairs, go to step 23 .
Repair short to voltage in HO2S 2 signal circuit. After repairs, go to step 23 .
Repair open or high resistance in HO2S 2 signal circuit. After repairs, go to step 23 .
Repair short to ground in HO2S 2 signal circuit. After repairs, go to step 23 .
Check for poor connections and terminal tension at ECM harness connector. Repair as necessary. After repairs, go to step 23 . If connections and terminals are okay, go to next step.
Replace ECM. New ECM must be programmed with theft deterrent module frequency code currently on vehicle. After repairs, go to next step.
Using scan tool, clear DTCs. Turn ignition off for 15 seconds. Start engine and operate vehicle as close to conditions recorded in FREEZE FRAME as possible. Check for DTCs. If DTC P0157 is set, go to step 2 . If DTC P0157 is not set, go to next step.
If other DTCs were present during OBD system check and have not been diagnosed, go to applicable DTC. If no other DTCs are present, system is okay.

DTC P0157: HO2S CIRCUIT-LOW VOLTAGE-BANK 2, SENSOR 2 (4.3L, 5.0L, 5.7L & 7.4L "C", "G", "K" & "P" SERIES)

Note. For circuit reference, see appropriate wiring diagram in WIRING DIAGRAMS article.

VCM supplies a voltage of about.45 volt between HO2S 2 signal and HO2S 2 ground circuits. HO2S 2 varies voltage from about one volt with rich exhaust to 0.1 volt with lean exhaust. HO2S 2 produces no voltage and acts as an open circuit when temperature is less than 600°F (316°C). DTC P0157, DTC P0158, an open sensor circuit or a cold sensor causes open loop operation. DTC P0157 determines if HO2S 2 or circuit is shorted low by checking for a lean condition during steady throttle and power enrichment.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-introduction__on-board-diagnostic-obd-system-check) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Install scan tool. Warm engine to normal operating temperature. Place gear selector in Park or Neutral. Apply parking brake. Increase engine speed to 1200 RPM. Monitor HO2S 2 voltage using scan tool. If voltage is fixed at less than.026 volt (4.3L, 5.0L and 5.7L) or less than.086 volt (7.4L), go to step 4 . If voltage is not as specified, go to next step.
DTC is intermittent. Check if additional DTCs are set. If any additional DTCs are set, go to applicable DTC test. If no additional DTCs are set, see «DIAGNOSTIC AIDS»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p0135-p0204) .
Turn ignition off. Disconnect HO2S 2 harness connector. Connect a jumper wire between HO2S 2 low circuit of HO2S 2 harness connector (VCM side) and ground. Turn ignition on, with engine off. Monitor HO2S 2 voltage using scan tool. If voltage is.35-.55 volt, go to next step. If voltage is not.35-.55 volt, go to step 6 .
Check for any condition that may cause HO2S 2 to detect a lean condition. Repair as necessary. After repairs, go to step 10 . If no problem is found, go to step 8 .
Turn ignition off. Remove jumper wire from HO2S 2 low circuit. Disconnect VCM harness connector containing HO2S 2 high signal circuit. Check for continuity between HO2S 2 high signal circuit and ground, and then between HO2S 2 high signal and low circuits. If no continuity is present in either circuit, go to step 9 . If continuity is present in either circuit, go to next step.
Repair HO2S 2 high signal circuit for short to ground or short to HO2S 2 low circuit. After repairs, go to step 10 .
Replace HO2S 2. After repairs, go to step 10 .
Replace VCM. Program replacement VCM using required equipment. Perform Passlock® reprogramming and CKP system variation learn procedures. After repairs, go to next step.
Using scan tool, clear DTCs. Start and warm engine to normal operating temperature. Select DTC, SPECIFIC, and then enter this DTC. Operate vehicle within the conditions for setting this DTC. If scan tool indicates that this test ran and passed, go to next step. If scan tool does not indicate that this test ran and passed, go to step 2 .
Using scan tool, select CAPTURE INFO, REVIEW INFO function If any undiagnosed DTCs are displayed, go to applicable DTC test. If no undiagnosed DTCs are displayed, system is okay.

Using scan tool, observe Long Term (LT) fuel trim values at different RPM and airflow conditions. Scan tool should display fuel trim cells so that LT fuel trim values can be check in each cell to determine when DTC may have set. If DTC is set, LT fuel trim values will be about 158 or greater.

Check for mispositioned HO2S wire pigtail contacting exhaust manifold. Check for intermittent ground in wire between connector and sensor. Check for poor VCM to engine block ground. Check for lean fuel injectors. Check for water near in-tank fuel pump inlet that may be delivered to injectors. Water causes a lean exhaust and can cause DTC to set.

DTC P0157: HO2S CIRCUIT-LOW VOLTAGE-BANK 2, SENSOR 2 (4.8L, 5.3L & 6.0L "C" & "K" SERIES & 5.7L "F" & "Y" BODIES)

Note. For circuit reference, see appropriate wiring diagram in WIRING DIAGRAMS article.

PCM supplies about 450 millivolts (mV) between HO2S 2 high and low signal circuits. The HO2S 2 voltage ranges from about 1000 mV when exhaust is rich to about 10 mV when exhaust is lean. PCM monitors and stores sensor voltage information and evaluates voltage samples to determine amount of time sensor voltage is out of range. If PCM detects HO2S 2 voltage is less than predetermined voltage, DTC P0157 will set.

For duplication of DTC, ensure

DTCs P0101, P0102, P0103, P0112, P0113, P0117, P0118, P0121, P0122, P0123, P0125, P0200, P0335, P0336, P0351-P0358 or P1258 are not set.
AIR, EGR and catalyst diagnostics not active.
Ignition voltage is greater than 9 volts.
Fuel system is operating in "closed loop".
TP sensor angle is between 2 and 70 percent.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-introduction__on-board-diagnostic-obd-system-check) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Start and warm engine to normal operating temperature. Operate vehicle under conditions required to set DTC. Using scan tool, select ENGINE 1 DATA LIST and monitor HO2S 2 voltage. If voltage is fixed less than 80 mV, go to step 4 . If voltage is not fixed less than 80 mV, go to next step.
Turn ignition on, with engine off. Using scan tool, review FREEZE FRAME and/or FAILURE RECORDS data and note parameters. Turn ignition off for about 15 seconds. Start engine and operate vehicle within conditions required for this diagnostic to run, and as close to conditions recorded in FREEZE FRAME/FAILURE RECORDS as possible. Select DTC function, and then enter DTC P0137. If scan tool indicates that this test failed this ignition, go to next step. If scan tool does not indicate that this test failed this ignition, see «DIAGNOSTIC AIDS»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p0135-p0204) .
Disconnect HO2S 2 connector. Connect a fused jumper wire between PCM connector (harness side), HO2S 2 low circuit and ground. If sensor voltage is 350-550 mV, see «DIAGNOSTIC AIDS»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p0135-p0204) . If sensor voltage is not 350-550 mV, go to next step.
Turn ignition off. Disconnect PCM harness connector C1. Check HO2S 2 signal circuit for short to ground or short to sensor ground circuit. Repair as necessary. After repairs, go to next step. If circuit(s) are okay, go to step 7 .
Repair HO2S 2 signal circuit. After repairs, go to step 8 .
Replace PCM. Program replacement PCM using required equipment. After repairs, go to next step.
Using scan tool, clear DTCs. Start and warm engine to normal operating temperature. Select DTC, SPECIFIC, and then enter DTC P0157. Operate vehicle within conditions for setting this DTC. If scan tool indicates that this test ran and passed, go to next step. If scan tool does not indicate that this test ran and passed, go to step 2 .
Using scan tool, select CAPTURE INFO, REVIEW INFO function. If any undiagnosed DTCs are displayed, go to applicable DTC test. If no undiagnosed DTCs are displayed, system is okay.

Check HO2S pigtail wire for breaks, contamination or grounding on exhaust manifold. Check for intermittent ground in signal wire between sensor connector and sensor.

DTC P0158: HO2S CIRCUIT-HIGH VOLTAGE-BANK 2, SENSOR 2 (3.0L "V" BODY)

Note. For circuit reference, see appropriate wiring diagram in WIRING DIAGRAMS article.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-introduction__on-board-diagnostic-obd-system-check) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Start and operate engine to normal operating temperature. Using scan tool, monitor HO2S 2 voltage. If voltage remains greater than 1083 mV, go to step 4 . If voltage does not remain greater than 1083 mV, go to next step.
Turn ignition on, with engine off. Review FREEZE FRAME data for this DTC and note parameters. Clear DTCs. Turn ignition off for 15 seconds. Start engine and operate vehicle as close to conditions recorded in FREEZE FRAME as possible. Check for DTCs. If DTC P0158 is set, go to next step. If DTC P0158 is not set, see «DIAGNOSTIC AIDS»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p0135-p0204) .
Turn ignition on, with engine off. Disconnect HO2S 2 harness connector. Check for signs of water or corrosion. Repair as necessary. If HO2S 2 voltage on scan tool is 375-525 mV, go to step 14 . If HO2S 2 voltage on scan tool is not 375-525 mV, go to next step.
Using DVOM, measure voltage between ground and signal circuit at HO2S 2 harness connector. If voltage is 900-1100 mV, go to next step. If voltage is not 900-1100 mV, go to step 11 .
Using DVOM, measure voltage between ground and low circuit at HO2S 2 harness connector. If voltage is 700-800 mV, go to step 22 . If voltage is not 700-800 mV, go to next step.
Continue to monitor voltage on HO2S 2 low circuit between harness connector and ground. Disconnect the 3 other HO2S harness connectors. As each sensor is disconnected, recheck voltage on DVOM. If disconnecting one of the other sensors restores voltage to 700-800 mV, go to step 14 . If disconnecting one of the other sensors does not restore voltage to 700-800 mV, go to next step.
Leave all HO2S harness connectors disconnected. Turn ignition off. Disconnect ECM harness connector located in engine compartment relay center. Turn ignition on. Using DVOM, check for voltage between ground and HO2S 2 low circuit at ECM harness connector. If no voltage is present, go to next step. If any voltage is present, go to step 15 .
Using DVOM, check harness continuity of HO2S 2 low circuit. If continuity is present, go to next step. If continuity is not present, go to step 16 .
Using DVOM, check harness continuity between HO2S 2 low circuit and ground. If continuity is present, go to step 17 . If continuity is not present, go to step 21 .
Leave all HO2S harness connectors disconnected. Turn ignition off. Disconnect ECM harness connector located in engine compartment relay center. Turn ignition on. Using DVOM, check for voltage between ground and HO2S 2 signal circuit at ECM harness connector. If any voltage is present, go to step 18 . If no voltage is present, go to next step.
Using DVOM, check harness continuity of HO2S 2 signal circuit. If continuity is present, go to next step. If continuity is not present, go to step 19 .
Using DVOM, check harness continuity between HO2S 2 signal circuit and ground. If continuity is present, go to step 20 . If continuity is not present, go to step 21 .
Replace shorted HO2S 2. After repairs, go to step 23 .
Repair short to voltage in HO2S 2 low circuit. After repairs, go to step 23 .
Repair open or high resistance in HO2S 2 low circuit. After repairs, go to step 23 .
Repair short to ground in HO2S 2 low circuit. After repairs, go to step 23 .
Repair short to voltage in signal circuit. After repairs, go to step 23 .
Repair open or high resistance in HO2S 2 signal circuit. After repairs, go to step 23 .
Repair short to ground in HO2S 2 signal circuit. After repairs, go to step 23 .
Check for poor connections and terminal tension at ECM harness connector. Repair as necessary. After repairs, go to step 23 . If connections and terminals are okay, go to next step.
Replace ECM. New ECM must be programmed with theft deterrent module frequency code currently on vehicle. After repairs, go to next step.
Using scan tool, clear DTCs. Turn ignition off for 15 seconds. Start engine and operate vehicle as close to conditions recorded in FREEZE FRAME as possible. Check for DTCs. If DTC P0158 is set, go to step 2 . If DTC P0158 is not set, go to next step.
If other DTCs were present during OBD system check and have not been diagnosed, go to applicable DTC. If no other DTCs are present, system is okay.

DTC P0158: HO2S CIRCUIT-HIGH VOLTAGE-BANK 2, SENSOR 2 (4.3L, 5.0L, 5.7L & 7.4L "C", "G", "K" & "P" SERIES)

Note. For circuit reference, see appropriate wiring diagram in WIRING DIAGRAMS article.

VCM supplies a voltage of about.45 volt between HO2S 2 signal and HO2S 2 ground circuits. HO2S 2 varies voltage from about one volt with rich exhaust to 0.1 volt with lean exhaust. HO2S 2 produces no voltage and acts as an open circuit when temperature is less than 600°F (316°C). DTC P0157, DTC P0158, an open sensor circuit or a cold sensor causes open loop operation. DTC P0158 determines if HO2S 2 or circuit is shorted high by checking for a rich condition during steady throttle.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-introduction__on-board-diagnostic-obd-system-check) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Install scan tool. Warm engine to normal operating temperature. Place gear selector in Park or Neutral. Apply parking brake. Increase engine speed to 1200 RPM. Monitor HO2S 2 voltage using scan tool. If voltage is fixed at greater than.994 volt on 4.3L, 5.0L and 5.7L or.976 volt on 7.4L, go to step 4 . If voltage is not as specified, go to next step.
Condition required to set DTC is not present at this time. Check for intermittent HO2S 2 circuit faults or any condition that may cause HO2S 2 to detect a rich condition. Repair as necessary. After repairs, go to step 10 . If no problem is found, see «DIAGNOSTIC AIDS»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p0135-p0204) .
Turn ignition off. Disconnect HO2S 2 harness connector. Connect a jumper wire between ground and HO2S 2 low circuit at HO2S 2 harness connector. Turn ignition on, with engine off. Monitor HO2S 2 voltage with scan tool. If voltage is 351-551 mV, go to next step. If voltage is not 351-551 mV, go to step 6 .
Check for any condition that may cause HO2S 2 to detect a rich condition. Check for contaminated HO2S 2. Repair as necessary. After repairs, go to step 10 . If no problem is found, go to step 8 .
Turn ignition off. Remove jumper wire from HO2S 2 low circuit. Disconnect VCM harness connector containing HO2S 2 high signal circuit. Turn ignition on, with engine off. Measure voltage between ground and HO2S 2 high signal circuit at HO2S 2 harness connector. If voltage is greater than 20 mV, go to next step. If voltage is not greater than 20 mV, go to step 9 .
Repair short to voltage in HO2S 2 high signal circuit. After repairs, go to step 10 .
Replace HO2S 2. After repairs, go to step 10 .
Replace VCM. Program replacement VCM using required equipment. Perform Passlock® reprogramming and CKP system variation learn procedures. After repairs, go to next step.
Using scan tool, clear DTCs. Start and warm engine to normal operating temperature. Select DTC, SPECIFIC, and then enter this DTC. Operate vehicle within the conditions for setting this DTC. If scan tool indicates that this test ran and passed, go to next step. If scan tool does not indicate that this test ran and passed, go to step 2 .
Using scan tool, select CAPTURE INFO, REVIEW INFO function. If any undiagnosed DTCs are displayed, go to applicable DTC test. If no undiagnosed DTCs are displayed, system is okay.

Check for an intermittent TP sensor output that will cause system to go rich due to false indication of throttle moving. Check for false rich indication due to silicone contamination of HO2S indicated by DTC accompanied by lean driveability conditions and a powdery white deposit on sensor.

DTC P0158: HO2S CIRCUIT-HIGH VOLTAGE-BANK 2, SENSOR 2 (4.8L, 5.3L & 6.0L "C" & "K" SERIES & 5.7L "F" & "Y" BODIES)

Note. For circuit reference, see appropriate wiring diagram in WIRING DIAGRAMS article.

For duplication of DTC, ensure

DTCs P0101, P0102, P0103, P0112, P0113, P0117, P0118, P0121, P0122, P0123, P0125, P0200, P0335, P0336, P0351-P0358 and P1258 are not set.
Ignition voltage is greater than 9 volts.
Fuel system is operating in closed loop.
TP sensor angle is 2-70 percent.
AIR, EGR and catalyst diagnostics are not active.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-introduction__on-board-diagnostic-obd-system-check) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Start engine and allow it to reach normal operating temperature. Increase engine speed to 1200 RPM. Monitor HO2S 2 voltage on scan tool. If voltage is greater than 930 mV, go to step 4 . If voltage is not greater than 930 mV, go to next step.
Turn ignition on, with engine off. Using scan tool, review FREEZE FRAME data and note parameters. Turn ignition off for 15 seconds. Start engine and operate vehicle within conditions required for setting this DTC, and as close to conditions recorded in FREEZE FRAME as possible. Monitor SPECIFIC DTC info for DTC P0158 until DTC P0158 test runs. If scan tool indicates test failed this ignition, go to next step. If scan tool does not indicated test failed this ignition, see «DIAGNOSTIC AIDS»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p0135-p0204) .
Turn ignition on, with engine off. Monitor HO2S 2 voltage with scan tool. If voltage is greater than 930 mV, go to next step. If voltage is not greater than 930 mV, see «DIAGNOSTIC AIDS»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p0135-p0204) .
Remove HO2S 2 heater fuse while monitoring HO2S 2 voltage. If voltage drops to 350-550 mV, go to next step. If voltage does not drop to 350-550 mV, go to step 7 .
Reinstall fuse. Disconnect HO2S 2 harness connector. Using a jumper wire, jumper HO2S 2 low circuit to ground. Monitor HO2S 2 voltage on scan tool. If voltage is 350-550 mV, go to step 10 . If voltage is not 350-550 mV, go to step 8 .
Turn ignition off. Disconnect PCM harness connector C1. Disconnect HO2S 2 harness connector. Turn ignition on. Check for voltage on HO2S 2 signal circuit at PCM harness connector. If any voltage is present, go to next step. If no voltage is present, go to step 9 .
Repair short to voltage in HO2S 2 signal circuit. After repairs, go to step 11 .
Replace PCM. Program replacement PCM using required equipment. After repairs, go to step 11 .
Replace HO2S 2. After repairs, go to next step.
Using scan tool, clear DTCs. Start engine and operate vehicle under conditions required to set DTC. If scan tool indicates this test ran and passed, go to next step. If scan tool does not indicate this test ran and passed, go to step 2 .
If scan tool displays any additional undiagnosed DTCs, go to applicable DTC test. If scan tool does not display any additional undiagnosed DTCs, system is okay.

DTC P0159: HO2S CIRCUIT-INSUFFICIENT ACTIVITY-BANK 1, SENSOR 2 (3.0L "V" BODY)

Note. For circuit reference, see appropriate wiring diagram in WIRING DIAGRAMS article.

For duplication of DTC, ensure fuel cut-off is enabled and HO2S 2 voltage is greater than.103 volt

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-introduction__on-board-diagnostic-obd-system-check) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Inspect for corrosion on HO2S 2 terminals. Ensure HO2S 2 is securely installed. Check terminal tension and for damaged wiring. Repair as necessary. After repairs, go to step 23 . If no problem is found, go to next step.
Turn ignition on, with engine off. Disconnect HO2S 2 harness connector. Using DVOM, measure voltage between ground and signal circuit at HO2S 2 harness connector. If voltage is 900-1100 mV, go to next step. If voltage is not 900-1100 mV, go to step 10 .
Using DVOM, measure voltage between ground and low circuit at HO2S 2 harness connector. If voltage is 700-800 mV, go to next step. If voltage is not 700-800 mV, go to step 6 .
Using a fused jumper, jumper HO2S 2 harness connector signal circuit to ground. Using scan tool, monitor HO2S 2 voltage. If voltage is -400 mV to -410 mV, go to step 20 . If voltage is not -400 mV to -410 mV, go to step 22 .
Continue to monitor voltage on HO2S 2 low circuit between harness connector and ground. Disconnect the 3 other HO2S harness connectors. As each sensor is disconnected, recheck voltage on DVOM. If disconnecting the other sensors restores voltage to 700-800 mV, go to step 13 . If disconnecting one of the other sensors does not restore voltage to 700-800 mV, go to next step.
Leave all HO2S harness connectors disconnected. Turn ignition off. Disconnect ECM connector located in engine compartment, in relay center. Turn ignition on. Using DVOM, check voltage between ground and HO2S 2 low circuit at ECM harness connector. If any voltage is present, go to step 14 . If no voltage is present, go to next step.
Using DVOM, check harness continuity of HO2S 2 low circuit. If continuity is present, go to next step. If continuity is not present, go to step 15 .
Using DVOM, check harness continuity between HO2S 2 low circuit and ground. If continuity is present, go to step 16 . If continuity is not present, go to step 21 .
Leave all HO2S harness connectors disconnected. Turn ignition off. Disconnect ECM harness connector located in engine compartment relay center. Turn ignition on. Using DVOM, check voltage between ground and HO2S 2 signal circuit at ECM harness connector. If any voltage is present, go to step 17 . If no voltage is present, go to next step.
Using DVOM, check harness continuity of HO2S 2 signal circuit. If continuity is not present, go to step 18 . If continuity is present, go to next step.
Using DVOM, check harness continuity between HO2S 2 signal circuit and ground. If continuity is present, go to step 19 . If continuity is not present, go to step 21 .
Replace shorted HO2S 2. After repairs, go to step 23 .
Repair short to voltage in HO2S 2 low circuit. After repairs, go to step 23 .
Repair open or high resistance in HO2S 2 low circuit. After repairs, go to step 23 .
Repair short to ground in HO2S 2 low circuit. After repairs, go to step 23 .
Repair short to voltage in HO2S 2 signal circuit. After repairs, go to step 23 .
Repair open or high resistance in HO2S 2 signal circuit. After repairs, go to step 23 .
Repair short to ground in HO2S 2 signal circuit. After repairs, go to step 23 .
Replace HO2S 2. After repairs, go to step 23 .
Check for poor connections and terminal tension at ECM harness connector. Repair as necessary. After repairs, go to step 23 . If connections and terminals are okay, go to next step.
Replace ECM. New ECM must be programmed with theft deterrent module frequency code currently on vehicle. After repairs, go to next step.
Using scan tool, clear DTCs. Turn ignition off for 15 seconds. Start engine and operate vehicle. Check for DTCs. If DTC P0159 is set, go to step 2 . If DTC P0159 is not set, go to next step.
If other DTCs were present during OBD system check and have not been diagnosed, go to applicable DTC. If no other DTCs are present, system is okay.

An exhaust leak may cause outside air to be pulled into exhaust gas stream past HO2S, causing this DTC to set. Check for exhaust leaks near HO2S.

DTC P0160: HO2S CIRCUIT-INSUFFICIENT ACTIVITY-BANK 2, SENSOR 2 (3.0L "V" BODY)

Note. For circuit reference, see appropriate wiring diagram in WIRING DIAGRAMS article.

Heated Oxygen Sensor (HO2S) produces a voltage that varies between -100 mV and 900 mV under normal operating conditions. Full operating range of HO2S circuit is about from -406 mV to 1124 mV. ECM monitors this voltage and determines if exhaust is lean or rich. Oxygen sensor voltage is high when exhaust is rich, and low when exhaust is lean. ECM constantly monitors HO2S signal during closed loop operation and compensates for rich or lean condition by decreasing or increasing injector pulse width as necessary. If HO2S 2 signal voltage remains at.401-.519 volt for more than one minute, DTC P0160 will set.

For duplication of DTC, ensure engine is running and battery voltage is greater than 11 volts.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-introduction__on-board-diagnostic-obd-system-check) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Inspect for corrosion on HO2S 2 terminals. Ensure HO2S 2 is securely installed. Check terminal tension and for damaged wiring. Repair as necessary. After repairs, go to step 23 . If no problem is found, go to next step.
Turn ignition on, with engine off. Disconnect HO2S 2 harness connector. Using DVOM, measure voltage between ground and signal circuit at HO2S 2 harness connector. If voltage is 900-1100 mV, go to next step. If voltage is not 900-1100 mV, go to step 10 .
Using DVOM, measure voltage between ground and low circuit at HO2S 2 harness connector. If voltage is 700-800 mV, go to next step. If voltage is not 700-800 mV, go to step 6 .
Using a fused jumper, jumper HO2S 2 harness connector signal circuit to ground. Using scan tool, monitor HO2S 2 voltage. If voltage is -400 mV to -410 mV, go to step 20 . If voltage is not -400 mV to -410 mV, go to step 22 .
Continue to monitor voltage on HO2S 2 low circuit between harness connector and ground. Disconnect the 3 other HO2S harness connectors. As each sensor is disconnected, recheck voltage on DVOM. If disconnecting the other sensors restores voltage to 700-800 mV, go to step 13 . If disconnecting one of the other sensors does not restore voltage to 700-800 mV, go to next step.
Leave all HO2S 2 harness connectors disconnected. Turn ignition off. Disconnect ECM harness connector located in engine compartment, in relay center. Turn ignition on. Using DVOM, check for voltage between ground and HO2S 2 low circuit at ECM harness connector. If any voltage is present, go to step 14 . If no voltage is present, go to next step.
Using DVOM, check harness continuity of HO2S 2 low circuit. If continuity is present, go to next step. If continuity is not present, go to step 15 .
Using DVOM, check harness continuity between HO2S 2 low circuit and ground. If continuity is present, go to step 16 . If continuity is not present, go to step 21 .
Leave all HO2S 2 harness connectors disconnected. Turn ignition off. Disconnect ECM harness connector located in engine compartment relay center. Turn ignition on. Using DVOM, check for voltage between ground and HO2S 2 signal circuit at ECM harness connector. If any voltage is present, go to step 17 . If no voltage is present, go to next step.
Using DVOM, check harness continuity of HO2S 2 signal circuit. If continuity is not present, go to step 18 . If continuity is present, go to next step.
Using DVOM, check harness continuity between HO2S 2 signal circuit and ground. If continuity is present, go to step 19 . If continuity is not present, go to step 21 .
Replace shorted HO2S 2. After repairs, go to step 23 .
Repair short to voltage in HO2S 2 low circuit. After repairs, go to step 23 .
Repair open or high resistance in HO2S 2 low circuit. After repairs, go to step 23 .
Repair short to ground in HO2S 2 low circuit. After repairs, go to step 23 .
Repair short to voltage in HO2S 2 signal circuit. After repairs, go to step 23 .
Repair open or high resistance in HO2S 2 signal circuit. After repairs, go to step 23 .
Repair short to ground in HO2S 2 signal circuit. After repairs, go to step 23 .
Replace HO2S 2. After repairs, go to step 23 .
Check for poor connections and terminal tension at ECM harness connector. Repair as necessary. After repairs, go to step 23 . If connections and terminals are okay, go to next step.
Replace ECM. New ECM must be programmed with theft deterrent module frequency code currently on vehicle. After repairs, go to next step.
Using scan tool, clear DTCs. Turn ignition off for 15 seconds. Start engine and operate vehicle. Check for DTCs. If DTC P0160 is set, go to step 2 . If DTC P0160 is not set, go to next step.
If other DTCs were present during OBD system check and have not been diagnosed, go to applicable DTC. If no other DTCs are present, system is okay.

An exhaust leak may cause outside air to be pulled into exhaust gas stream past HO2S, causing this DTC to set. Check for exhaust leaks near HO2S.

DTC P0160: HO2S CIRCUIT-INSUFFICIENT ACTIVITY-BANK 2, SENSOR 2 (4.3L, 5.0L, 5.7L & 7.4L "C", "G", "K" & "P" SERIES)

Note. For circuit reference, see appropriate wiring diagram in WIRING DIAGRAMS article.

HO2S 2 heater provides for faster sensor warm-up allowing sensor to become active in a shorter period of time and remain active during long extended idle. If HO2S 2 voltage remains 399-473 mV for more than 100 seconds, DTC P0160 will set.

For duplication of DTC, ensure

No misfire, EVAP system, ECT, IAT, MAF, MAP or TP sensor DTCs are set.
No intrusive tests are in progress.
No device controls are active.
System voltage is at least 9 volts.
Engine run time is greater than 2 minutes.
Deceleration Fuel Cut-Off (DFCO) mode is not active.
Engine coolant temperature is 138°F (59°C) or greater.
MAF is 13 gm/s or greater.
DTC P0155 is not active.
System is in closed loop.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-introduction__on-board-diagnostic-obd-system-check) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Using scan tool, store DTC information from VCM. Clear DTCs and reset fuel trim values. Start engine and allow it to reach normal operating temperature. Monitor HO2S 2 voltage on scan tool. If voltage is fixed at 400-473 mV, go to step 4 . If voltage is not as specified, go to next step.
Condition that set DTC is not present at this time. If any additional DTCs are set, go to applicable DTC test. If no additional DTCs are set, see «DIAGNOSTIC AIDS»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p0135-p0204) .
Turn ignition off. Disconnect HO2S 2 harness connector. Using jumper wires, jumper HO2S 2 high signal and low circuits to ground. Turn ignition on. Monitor HO2S 2 voltage with scan tool. If voltage is less than 20 mV, go to step 7 . If voltage is not less than 20 mV, go to next step.
Turn ignition off. Remove jumper wires. Disconnect VCM harness connector containing HO2S 2 circuits. Measure resistance of HO2S 2 high signal and low circuits between HO2S 2 and VCM. If resistance of both circuits is less than 5 ohms, go to next step. If resistance of either circuit is not less than 5 ohms, go to step 9 .
Check VCM harness connections. Repair as necessary. After repairs, go to step 17 . If connections are okay, go to step 16 .
Remove jumper wires from HO2S 2. Turn ignition on. Connect test light between HO2S 2 heater ignition feed and ground circuits at HO2S 2 harness connector. If test light illuminates, go to next step. If test light does not illuminate, go to step 10 .
Turn ignition off. Reconnect HO2S 2 harness connector. Disconnect VCM harness connector containing HO2S 2 low circuit and VCM harness connector containing VCM ground circuits. Measure resistance between HO2S 2 low circuit and one of the VCM ground circuit terminals at VCM harness connector. If resistance is less than 500 ohms, go to step 12 . If resistance is not less than 500 ohms, go to step 11 .
Repair circuit with high resistance. After repairs, go to step 17 .
Repair HO2S 2 heater ignition feed or ground circuit. After repairs, go to step 17 .
Repair high resistance between HO2S 2 low circuit and VCM ground circuit. After repairs, go to step 17 .
Check for exhaust leaks upstream of HO2S 2. Repair as necessary. After repairs, go to step 17 . If no leaks are found, go to next step.
Allow engine to completely cool. Measure resistance between HO2S 2 low circuit and one of the VCM ground circuit terminals at VCM harness connector. If resistance is less than 500 ohms, go to step 15 . If resistance is not less than 500 ohms, go to next step.
Remove HO2S 2. Clean threads and apply anti-seize compound, and then reinstall. Measure resistance between HO2S 2 low circuit and one of the VCM ground circuit terminals at VCM harness connector. If resistance is less than 500 ohms, go to step 17 . If resistance is not less than 500 ohms, go to next step.
Replace HO2S 2. After repairs, go to step 17 .
Replace VCM. Program replacement VCM using required equipment. Perform Passlock® reprogramming and CKP system variation learn procedures. After repairs, go to next step.
Using scan tool, clear DTCs. Start engine and operate vehicle under conditions required to set this DTC. If scan tool indicates this test ran and passed, go to next step. If scan tool does not indicate this test ran and passed, go to step 2 .
Using scan tool, select CAPTURE INFO, REVIEW INFO function. If any undiagnosed DTCs are displayed, go to applicable DTC test. If no undiagnosed DTCs are displayed, system is okay.

With ignition on and engine off, HO2S 2 voltage on scan tool should gradually decrease to less than.15 volt indicating heater is operating properly. If voltage does not decrease as specified, disconnect HO2S 2 harness connector and connect a test light between HO2S 2 harness connector terminals "C" and "D" (engine harness side). If test light illuminates, replace HO2S 2. If test light does not illuminate, repair open in HO2S 2 heater ground circuit or HO2S 2 ignition feed circuit.

DTC P0160: HO2S CIRCUIT-INSUFFICIENT ACTIVITY-BANK 2, SENSOR 2 (4.8L, 5.3L & 6.0L "C" & "K" SERIES & 5.7L "F" & "Y" BODIES)

Note. For circuit reference, see appropriate wiring diagram in WIRING DIAGRAMS article.

PCM supplies about 450 millivolts (mV) between HO2S 2 high and low signal circuits. HO2S 2 voltage ranges from about 1000 mV when exhaust is rich to about 10 mV when exhaust is lean. PCM monitors and stores sensor voltage information and evaluates voltage samples to determine amount of time sensor voltage is out of range. If PCM detects HO2S 2 voltage is out bias range, DTC P0160 will set.

For duplication of DTC, ensure

DTCs P0101, P0102, P0103, P0112, P0113, P0117, P0118, P0121, P0122, P0123, P0125, P0200, P0335, P0336, P0351-P0358, P1120, P1220, P1221 or P1258 are not set.
Engine has been running for more than 70 seconds.
Fuel system is operating in closed loop.
System voltage is greater than 9 volts.
AIR, EGR and catalyst diagnostics are not active.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-introduction__on-board-diagnostic-obd-system-check) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Start and warm engine to normal operating temperature. Increase engine speed to greater than 1200 RPM for 2 minutes. Using scan tool, select ENGINE 1 DATA LIST and monitor HO2S 2 voltage. If voltage is varying outside of 350-550 mV range, go to next step. If voltage is not as specified, go to step 4 .
Turn ignition on, with engine off. Using scan tool, review FREEZE FRAME and/or FAILURE RECORDS data and note parameters. Turn ignition off for about 15 seconds. Start engine and operate vehicle within conditions required for this diagnostic to run, and as close to conditions recorded in FREEZE FRAME/FAILURE RECORDS as possible. Select DTC function, and then enter DTC P0160. If scan tool indicates that this test failed this ignition, go to next step. If scan tool does not indicate that this test failed this ignition, see «DIAGNOSTIC AIDS»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p0135-p0204) .
Turn ignition on, with engine off. Disconnect HO2S 2 harness connector. Connect a fused jumper wire between ground and PCM connector (harness side) HO2S 2 high and low signal circuits. If voltage is less than 200 mV, go to step 8 . If voltage is not less than 200 mV, go to next step.
Remove jumper wire from HO2S 2 low signal circuit. Using DVOM, measure voltage between ground and HO2S 2 low signal circuit at HO2S 2 harness connector. If voltage is about 5 volts, go to next step. If voltage is not about 5 volts, go to step 7 .
Turn ignition off. Disconnect PCM harness connector C1. Check for continuity in HO2S 2 high signal circuit. If continuity is present, go to step 10 . If continuity is not present, repair as necessary. After repairs, go to step 12 .
Turn ignition off. Disconnect PCM harness connector C1. Check for continuity in HO2S 2 low signal circuit. If continuity is present, go to step 10 . If continuity is not present, repair as necessary. After repairs, go to step 12 .
Check HO2S 2 circuits for poor connections at HO2S 2 harness connector. Repair as necessary. After repairs, go to step 12 . If connections are okay, go to next step.
Replace HO2S 2. After repairs, go to step 12 .
Check HO2S 2 circuits for poor connection at PCM. Repair as necessary. After repairs, go to step 12 . If connections are okay, go to next step.
Replace PCM. Program replacement PCM using required equipment. After repairs, go to next step.
Using scan tool, clear DTCs. Start and warm engine to normal operating temperature. Select DTC, SPECIFIC, and then enter DTC P0160. Operate vehicle within conditions for setting this DTC. If scan tool indicates that this test ran and passed, go to next step. If scan tool does not indicate that this test ran and passed, go to step 2 .
Using scan tool, select CAPTURE INFO, REVIEW INFO function. If any undiagnosed DTCs are displayed, go to applicable DTC test. If no undiagnosed DTCs are displayed, system is okay.

Oxygen supply inside HO2S 2 is necessary for its proper operation. This supply of oxygen is provided through HO2S 2 wires. Inspect all wires and terminals for breaks or contamination.

DTC P0161: HO2S HEATER CIRCUIT-BANK 2, SENSOR 2 (3.0L "V" BODY)

Note. For circuit reference, see appropriate wiring diagram in WIRING DIAGRAMS article.

When HO2S 2 is cold, signal voltage at ECM is about 450 mV. When ignition is turned to on position, switched battery voltage is supplied to HO2S heaters via power relay. ECM controls heater operation by first modulating ground circuit when sensors are cold, and then turning them on continuously after predetermined amount of time. This prevents possibility of thermal shock to sensors by controlling sensor's rate of heating. As heater reaches operating temperature, HO2S 2 voltage responds by changing from bias voltage range to normal operation.

On cold start, ECM will track how much time it takes for HO2S 2 voltage to become greater than or less than bias voltage range. If ECM determines that it took too much time for HO2S 2 to enter into normal operating range, DTC P0161 will set. The time it takes HO2S 2 to reach operating temperature is based on amount of airflow into engine and start-up coolant temperature.

For duplication of DTC, ensure battery voltage is greater than 11 volts, and no HO2S 2 DTCs are present.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-introduction__on-board-diagnostic-obd-system-check) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Disconnect HO2S 2 harness connector. Using test light connected to ground, probe HO2S 2 harness connector switched battery feed circuit. If test light illuminates, go to next step. If test light does not illuminate, go to step 4 .
Start engine. Using test light connected to battery positive, probe HO2S 2 harness connector heater control circuit. If test light illuminates, go to step 9 . If test light does not illuminate, go to step 8 .
Check HO2S 2 heater fuse. If fuse is okay, go to next step. If fuse is open, go to step 6 .
Using test light connected to ground, check for power at HO2S 2 fuse. If test light illuminates, go to step 11 . If test light does not illuminate, go to step 12 .
Disconnect other HO2S 2 harness connector. Using test light connected to battery positive, probe HO2S 2 harness connector switched battery feed circuit. If test light illuminates, go to step 13 . If test light does not illuminate, go to next step.
Using DVOM, measure resistance of both HO2S 2 heaters at sensor pigtails. If resistance of both heaters is greater than 4 ohms, see «DIAGNOSTIC AIDS»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p0135-p0204) . If resistance of both heaters is 4 ohms or less, go to step 14 .
Turn ignition off. Disconnect ECM harness connector located in engine compartment relay center. Using DVOM, check for continuity in heater control circuit between HO2S 2 and ECM harness connectors. If continuity is present, go to step 16 . If continuity is not present, go to step 15 .
Check for poor connections and terminal tension at HO2S 2 harness connector. Repair as necessary. After repairs, go to step 18 . If connections and terminals are okay, go to next step.
Replace HO2S 2. After repairs, go to step 18 .
Repair open or high resistance in switched battery feed circuit between fuse and HO2S 2. After repairs, go to step 18 .
Repair feed circuit to fuse. After repairs, go to step 18 .
Repair short to ground in switched battery feed circuit. After repairs, go to step 18 .
Replace HO2S 2 with low resistance heater. After repairs, go to step 18 .
Repair open or high resistance in heater control circuit. After repairs, go to step 18 .
Check for poor connections and terminal tension at ECM harness connector. Repair as necessary. After repairs, go to step 18 . If connections and terminals are okay, go to next step.
Replace ECM. New ECM must be programmed with theft deterrent module frequency code currently on vehicle. After repairs, go to next step.
Using scan tool, clear DTCs. Turn ignition off for 15 seconds. Start engine and operate vehicle. Check for DTCs. If DTC P0161 is set, go to step 2 . If DTC P0161 is not set, go to next step.
If other DTCs were present during OBD system check and have not been diagnosed, go to applicable DTC. If no other DTCs are present, system is okay.

DTC P0161: HO2S HEATER CIRCUIT-BANK 2, SENSOR 2 (4.3L, 5.0L, 5.7L & 7.4L "C", "G", "K" & "P" SERIES)

Note. For circuit reference, see appropriate wiring diagram in WIRING DIAGRAMS article.

HO2S 2 heater provides for faster sensor warm-up allowing sensor to become active in a shorter period of time and remain active during long extended idle. DTC determines if HO2S 2 heater is operating properly by monitoring amount of time necessary for HO2S 2 to become active after start-up.

For duplication of DTC, ensure

System voltage is greater than 9 volts but less than 17 volts.
MAF is less than 27 gm/s on 4.3L and 7.4L, or less than 35 gm/s on 5.0L and 5.7L.
Engine run time is greater than 2 seconds.
ECT and IAT is less than 91°F (33°C).
Difference between ECT and IAT is less than 41°F (5°C).

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-introduction__on-board-diagnostic-obd-system-check) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Install scan tool. Turn ignition on, with engine off. Immediately record HO2S 2 voltage using scan tool. Monitor voltage for 2 minutes. If voltage gradually increases or decreases by.15 volt (150 mV), go to next step. If voltage does not gradually increase or decrease by.15 volt (150 mV), go to step 4 .
Condition required to set DTC is not present at this time. Check for damaged HO2S 2 or intermittent HO2S 2 circuit faults. Repair as necessary. After repairs, go to step 14 . If no problem is found, see «DIAGNOSTIC AIDS»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p0135-p0204) .
Turn ignition off. Disconnect HO2S 2 harness connector. Connect test light between heater ignition feed and ground circuits at HO2S 2 harness connector. Turn ignition on. If test light illuminates, go to next step. If test light does not illuminate, go to step 6 .
Remove test light. Using jumper wires, connect HO2S 2 high signal and low circuits to ground. Ensure ignition is on. Monitor HO2S 2 voltage with scan tool. If voltage is less than 20 mV, go to step 8 . If voltage is not less than 20 mV, go to step 7 .
Connect test light between ground and heater ignition feed circuit at HO2S 2 harness connector. If test light illuminates, go to step 9 . If test light does not illuminate, go to step 10 .
Turn ignition off. Remove jumper wires. Disconnect VCM harness connectors containing HO2S 2 high signal and low circuits. Measure resistance of HO2S 2 high signal and low circuits. If resistance of each circuit is less than 5 ohms, go to step 12 . If resistance of either circuit is not less than 5 ohms, go to step 11 .
Replace HO2S 2. After repairs, go to step 14 .
Repair open in HO2S 2 heater ground circuit. After repairs, step 14 .
Repair no voltage condition on HO2S 2 heater ignition feed circuit. After repairs, go to step 14 .
Repair circuit that measured high resistance. After repairs, go to step 14 .
Check for faulty VCM harness connections. Repair as necessary. After repairs, go to step 14 . If connections are okay, go to next step.
Replace VCM. Program replacement VCM using required equipment. Perform Passlock® reprogramming and CKP system variation learn procedures. After repairs, go to next step.
Turn ignition on, with engine off. Immediately record HO2S 2 voltage using scan tool. Monitor voltage for 2 minutes. If voltage gradually increases or decreases by.15 volt (150 mV), go to next step. If voltage does not gradually increase or decrease by.15 volt (150 mV), go to step 4 .
Using scan tool, select CAPTURE INFO, REVIEW INFO function. If any undiagnosed DTCs are displayed, go to applicable DTC test. If no undiagnosed DTC are displayed, system is okay.

DTC P0161: HO2S HEATER CIRCUIT-BANK 2, SENSOR 2 (4.8L, 5.3L & 6.0L "C" & "K" SERIES & 5.7L "F" & "Y" BODIES)

Note. For circuit reference, see appropriate wiring diagram in WIRING DIAGRAMS article.

PCM supplies a bias voltage (about 450 millivolts) on HO2S 2 high signal and low circuits. When ignition is turned on, battery voltage is supplied to HO2S 2 heater. As oxygen sensor heater reaches operating temperature, HO2S 2 voltage responds by changing from a bias voltage range to normal operation (less than 300 millivolts). Depending on exhaust gas content, it is possible for HO2S 2 voltage to increase to greater than 450 mV.

PCM will run heater test only on a cold start and once during ignition cycle. When engine is started, PCM will determine how much time it takes HO2S 2 voltage to increase or decrease from bias range threshold. If PCM detects that it took too much time to enter into normal operating range, DTC P0161 will set. Time it takes HO2S 2 to reach operating temperature is based on amount of air that flows into engine.

For duplication of DTC, ensure

DTCs P0101, P0102, P0103, P0112, P0113, P0117, P0118, P0121, P0122, P0123, P0125, P0200, P0335, P0336, P0351-P0358 or P1258 are not set.
ECT and IAT temperatures are less than 122°F (50°C) and within 46°F (8°C) of each other.
Ignition voltage is 10-18 volts.
AIR, EGR and catalyst diagnostics are not active.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-introduction__on-board-diagnostic-obd-system-check) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Turn ignition off. Turn ignition on, with engine off. Using scan tool, select ENGINE 1 DATA LIST and monitor HO2S 2 voltage. If voltage changes from bias voltage to greater than 700 mV or less than 300 mV, see «DIAGNOSTIC AIDS»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p0135-p0204) . If voltage does not change from bias voltage to less than 300 mV or greater than 700 mV, go to next step.
Check HO2S 2 ignition feed fuse. If fuse is open, go to step 11 . If fuse is okay, go to next step.
Raise and support vehicle. Disconnect HO2S 2 harness connector. Connect test light to chassis ground and probe ignition feed circuit at HO2S 2 harness connector. If test light illuminates, go to next step. If test light does not illuminate, go to step 7 .
Connect test light between ignition feed circuit and heater ground circuit at HO2S 2 harness connector. If test light illuminates, go to next step. If test light does not illuminate, go to step 8 .
Using DVOM, measure resistance between ignition feed and heater ground circuits at HO2S 2 harness connector. Resistance should be 3.5-14.0 ohms. If resistance is as specified, go to step 9 . If resistance is not as specified, go to step 10 .
Repair open in HO2S 2 ignition feed circuit. After repairs, go to step 12 .
Repair open in HO2S 2 heater ground circuit. After repairs, go to step 12 .
Check for poor terminal connection at HO2S 2 harness connector. Repair as necessary. After repairs, go to step 12 . If connections are okay, go to next step.
Replace HO2S. After repairs, go to step 12 .
Locate and repair short to ground in HO2S 2 ignition feed circuit and replace fuse. After repairs, go to next step.
Using scan tool, clear DTCs. Start and warm engine to normal operating temperature. Select DTC, SPECIFIC, and then enter DTC P0161. Operate vehicle within conditions for setting this DTC. If scan tool indicates that this test ran and passed, go to next step. If scan tool does not indicate that this test ran and passed, go to step 2 .
Using scan tool, select CAPTURE INFO, REVIEW INFO function. If any undiagnosed DTCs are displayed, go to applicable DTC test. If no undiagnosed DTCs are displayed, system is okay.

FAIL COUNTER and PASS COUNTER can also be used to determine how many ignition cycles diagnostic reported a pass and/or fail condition. Operate vehicle within same freeze frame conditions (RPM, load, vehicle speed, temperature, etc.) that are noted. This will isolate when DTC failed.

HO2S heater diagnostic will only run once on a cold start and only once per ignition cycle. Oxygen supply inside HO2S is necessary for proper operation and is provided through HO2S wires. Check all HO2S wires and connections for breaks or contamination.

The front oxygen sensor sends signals on exhaust gas oxygen content to the PCM to control a 14.7:1 air/fuel ratio under normal driving conditions. PCM can make fuel corrections based on this input, by increasing or decreasing injector pulse width (fuel trim). When certain conditions have been met to begin learning fuel control (ECT, closed loop, etc.), the PCM will use the short term fuel trim cell to update one of the 4 long term cells (idle, decel, cruise, accel) being used.

During every drive cycle (trip) PCM will use and update the idle and cruise long term cells and will keep track of how long the control system is operating in these cells. After about 2 minutes of being in each of these cells, the fuel control system will enable EVAP purge (purge on) and the purge long term cells will be used. If average of the idle and cruise fuel cells is 147 and the short fuel trim cell is currently over 128, a lean fuel system DTC will set. This test is performed before the purge cells are used.

DTC will set if the averaged long term idle and cruise fuel trim cells are 147 and the current short term fuel trim cell is greater than 128 for 3 seconds when PCM is using the non-purge long term fuel trim cells, system is in closed loop, coolant temperature is 140-239°F (60-115°C), airflow is 2-80 gm/s, MAP at 3-12 psi (.2-.8 kg/cm 2 ), RPM at 500-4000 RPM, TP is less than 75 percent open, BARO at greater than 10 psi (.7 kg/cm 2 ), IAT -22°F (-30°C) to 176°F (80°C), vehicle speed less than 75 MPH and no ECT, MAP, IAT, TP sensor, VSS, EVAP canister purge, front O2S DTCs or DTC P0125 not present. Fuel control system is continuously checked when these conditions have been met.

A lean condition can be caused by a vacuum leak, fuel pressure too low, water in fuel or an exhaust leak around manifold or in front of O2S.

If the front O2S and the rear HO2S voltage reading is less than 300 mV all the time, the oxygen sensors are probably not at fault.

PCM monitors oxygen sensor signal voltage and adjusts fuel delivery based on signal voltage. A change made to fuel delivery is indicated by the long and short term fuel trim values. Ideal fuel trim value is about 128 (zero percent).

A fuel trim value of greater than 128 indicates that PCM is adding fuel to compensate for a lean condition. A fuel trim value less than 128 indicates that PCM is reducing amount of fuel to compensate for rich condition. DTC P0171 will set if PCM detects an excessively lean condition.

For duplication of DTC, ensure

DTCs P0105, P0107, P0108, P0112, P0113, P0117, P0118, P0122, P0123, P0125, P0131-P0134, P0200, P0300-P0304, P0325, P0335, P0341, P0342, P0446, P0502, P0503, P0506, P0507, P0601, P0602, P1133 or P1441 are not set.
IAT is -13 to 175°F (-25 to 115°C).
ECT is 140-239°F (60-115°C).
Engine speed is 550-3400 RPM.
Vehicle speed is less than 82 MPH.
MAP is greater than 28 kPa.
BARO is greater than 72 kPa.
EVAP purge is not occurring.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-introduction__on-board-diagnostic-obd-system-check) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
If any other DTCs are set, diagnose DTCs as necessary before proceeding. If no other DTCs are set, go to next step.
Start and warm engine to normal operating temperature. Ensure system is in closed loop. Using scan tool, select FUEL TRIM INDEX. If fuel trim index is less than 29 percent, go to next step. If fuel trim index is not less than 29 percent, go to step 5 .
Turn ignition on, with engine off. Using scan tool, review FREEZE FRAME data and note parameters. Start engine and operate vehicle within conditions required for setting this DTC, and as close to conditions recorded in FREEZE FRAME as possible. If fuel trim index is less than 29 percent, go to step 16 . If fuel trim index is not less than 29 percent, go to next step.
Check vacuum hoses for splits, kinks and proper routing. Check PCV valve for proper installation. Check for fuel contamination. Check PCM and sensor grounds. Check O2S 1 for correct installation and ensure O2S 1 wiring is not in contact with exhaust manifold. If no problems are found, go to next step. If any problem is found, go to step 7 .
Disconnect MAP sensor harness connector. Operate vehicle in closed loop while monitoring FUEL INDEX TRIM. If fuel trim index is less than 29 percent, go to step 15 . If fuel trim index is not less than 29 percent, go to step 9 .
Repair fault that was detected in step 5) . Operate vehicle in closed loop while monitoring FUEL INDEX TRIM. If fuel trim index is less than 29 percent, go to next step. If fuel trim index is not less than 29 percent, go to step 9 .
Lean condition is not present at this time. If a driveability problem exists, see appropriate TROUBLE SHOOTING - NO CODES article. If no driveability problem exist, go to step 16 .
Check vacuum hoses for splits, kinks and proper routing. Check throttle body, intake manifold and injector "O" rings for vacuum leaks. Repair as necessary. After repairs, go to step 16 . If no problem is found, go to next step.
Start engine and allow it to idle. Using scan tool, check IAC count. If IAC count is greater than 5, go to next step. If IAC count is not greater than 5, go to step 12 .
Check for fuel contamination. Repair as necessary. After repairs, go to step 16 . If fuel is okay, go to step 13 .
Turn ignition off. Perform DTC P0506 or P0507 to check IAC valve performance. Repair as necessary. After repairs, go to step 16 . If IAC valve is okay, go to next step.
Connect a fuel pressure gauge to fuel system. Cycle ignition switch 2-3 times. With fuel pump running, observe fuel pressure. If fuel pressure is 42-55 psi (290-379 kPa), go to next step. If fuel pressure is not as specified, repair fuel system as necessary. See appropriate SYSTEM & COMPONENT TESTING article.
Ensure engine is at normal operating temperature. Start engine and allow it to idle. Observe fuel pressure. Fuel pressure noted in step 13) should drop 3-10 psi (21-69 kPa). If fuel pressure is as specified, perform injector balance test. See FUEL SYSTEM in appropriate SYSTEM & COMPONENT TESTING article. If fuel pressure is not as specified, see BASIC FUEL SYSTEM CHECKS in appropriate BASIC DIAGNOSTIC PROCEDURES article.
Replace MAP sensor. After repairs, go to next step.
Using scan tool, clear DTCs. Start engine and allow it to idle. Ensure engine is at normal operating temperature. Operate vehicle within conditions required for setting this DTC. Select SPECIFIC DTC function, and then enter DTC P0171. If scan tool indicates this test ran and passed, go to next step. If scan tool does not indicate this test ran and passed, go to step 2 .
If any other DTCs are set, diagnose DTCs as necessary. If no other DTCs are set, system is okay.

If DTC P0171 cannot be duplicated, problem may have been caused by engine running out of fuel. A fuel delivery malfunction will cause DTC to set. Check all items that can cause a lean condition.

An intermittent problem can be caused by misrouted harness, rubbed-through wire insulation or broken wire inside insulation. DO NOT attempt to repair damaged oxygen sensor connector or wiring. If damage is detected, replace oxygen sensor.

DTC P0171: FUEL TRIM SYSTEM LEAN-BANK 1 (3.0L "V" BODY)

Note. For circuit reference, see appropriate wiring diagram in WIRING DIAGRAMS article.

To provide the best possible combination of driveability, fuel economy and emission control, a closed loop air/fuel metering system is used. While in closed loop, ECM monitors heated oxygen sensor signal voltage and adjusts fuel delivery based on signal voltage. A change made in fuel delivery will be indicated by long and short term fuel trim values. Short term fuel trim values change rapidly in response to HO2S signal voltages. These changes fine tune engine fueling.

Long term fuel trim values change in response to trends in short term fuel trim. Long term fuel trim makes coarse adjustments to fueling in order to re-center and restore control to short term fuel trim. Short and long term fuel trim can be monitored with a scan tool. Ideal fuel trim values are around zero percent. A positive fuel trim value indicates ECM is adding fuel to compensate for lean condition. A negative fuel trim value indicates ECM is reducing amount of fuel to compensate for rich condition.

If an excessively rich or lean condition is detected, ECM will set a DTC. Long term (additive and multiplicative) fuel trim diagnostic parameter is a calculated value from several of long term speed loan learn cells which are selected based on speed and load.

For duplication of DTC, ensure system is in closed loop and fuel trim is enabled.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-introduction__on-board-diagnostic-obd-system-check) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
If any other DTCs are set, except DTCs P0171 and P0174, proceed to that DTC first before proceeding with this diagnostic procedure. If no other DTCs are set, start engine and allow it to reach normal operating temperature. Ensure fuel system is in closed loop. Using scan tool, monitor short term and long term fuel trim for bank 1. If both parameters are less than 95 percent, go to next step. If both parameters are not less than 95 percent, go to step 4 .
Turn ignition on, with engine off. Review FREEZE FRAME data for this DTC and note parameters. Clear DTCs. Turn ignition off for 15 seconds. Start engine and operate vehicle as close to conditions recorded in FREEZE FRAME as possible. Check for DTCs. If DTC P0171 is set, go to next step. If DTC P0171 is not set, see «DIAGNOSTIC AIDS»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p0135-p0204) .
If DTC P0174 is also set, go to next step. If DTC P0174 is not set, go to step 6 .
Inspect vacuum hoses for splits, kinks and proper connections. Check throttle body and intake manifold for vacuum leaks. Check PCV valve operation and for system leaks. Inspect fuel system for contaminated fuel. Ensure ECM and sensor grounds are clean, tight and in correct locations. Inspect air induction system after MAF sensor for air leaks. Inspect engine for mechanical failure. Repair components as necessary. After repairs, go step 7 . If all components are okay, diagnose fuel system malfunction. See BASIC FUEL SYSTEM CHECKS in appropriate BASIC DIAGNOSTIC PROCEDURES article.
Inspect bank 1 for exhaust leaks, and for missing or loose exhaust hardware. Ensure bank 1 HO2S 1 is installed securely and electrical connector is not contacting exhaust system or ignition wires. Check for vacuum leaks which only affect bank 1 (intake manifold, injector "O" rings). Inspect for engine mechanical failure. Repair components as necessary. After repairs, go to next step. If all components are okay, diagnose fuel system malfunction. See BASIC FUEL SYSTEM CHECKS in appropriate BASIC DIAGNOSTIC PROCEDURES article.
Using scan tool, clear DTCs. Turn ignition off for 15 seconds. Start engine and operate vehicle as close to conditions recorded in FREEZE FRAME as possible. Check for DTCs. If DTC P0171 is set, go to step 2 . If DTC P0171 is not set, go to next step.
If other DTCs were present during OBD system check and have not been diagnosed, go to applicable DTC. If no other DTCs are present, system is okay.

If DTC P0171 cannot be duplicated, DTC may have been caused by customer running vehicle out of fuel. Fuel system will be lean if pressure is too low. It may be necessary to monitor fuel pressure while driving vehicle at various speeds and/or loads to confirm this condition. Inspect for water in fuel system. Water, even in small amounts, near in-tank fuel pump inlet, can be delivered to injector. Water causes a lean exhaust and can set this DTC.

DTC P0171: FUEL TRIM SYSTEM LEAN (3.1L "N" & "W" BODIES & 3.4L "N" BODY & "U" SERIES)

Note. For circuit reference, see appropriate wiring diagram in WIRING DIAGRAMS article.

PCM reads HO2S signal voltage and adjusts fuel delivery based on this voltage. A change made to fuel delivery is indicated by Long Term (LT) and Short Term (ST) fuel trim values.

ST fuel trim values change rapidly in response to HO2S signal voltages. These changes fine tune engine fueling. LT fuel trim values change in response to trends in ST fuel trim. LT fuel trim makes coarse adjustments to fueling in order to re-center and restore control to ST fuel trim. LT and ST fuel trim can be read by using a scan tool.

Ideal fuel trim value is about zero. Fuel trim value greater than zero indicates that PCM is adding fuel to compensate for a lean condition. Fuel trim less than zero indicates that PCM is reducing amount of fuel to compensate for rich condition. DTC P0171 will set if PCM detects an excessively rich or lean condition.

For duplication of DTC, ensure

No EVAP system, EST, HO2S, fuel injector circuit, EGR, misfire, idle speed, vehicle speed, MAF, ECT, TP, CKP, CMP, MAP or IAT sensor DTCs are set.
ECT is 68-230°F (20-110°C).
IAT is -4 to 149°F (-20 to 65°C) on 3.1L or 0-158°F (-18 to 70°C) on 3.4L.
BARO is greater than 70 kPa.
MAP is 2.6-11.6 psi (18-80 kPa).
TP angle is less than 90 percent.
Vehicle speed is less than 70 MPH.
MAF is 3-150 grams per second.
Engine speed is 550-5000 RPM on 3.1L or 600-4000 RPM on 3.4L.
Long term fuel trim is near maximum authority (+16 percent).
Short term fuel trim is near maximum authority (+20 percent).

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-introduction__on-board-diagnostic-obd-system-check) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
If any other DTCs are set, diagnose affected DTCs before proceeding. If no other DTCs are set, go to next step.
Operate vehicle in closed loop mode while using scan tool to read LT and ST FUEL TRIM values. If LT FUEL TRIM value is about +16 percent and ST FUEL TRIM value is about +20 percent, go to step 5 . If values are not as specified, go to next step.
Using scan tool, read and record FAILURE RECORDS data. Clear DTCs and operate vehicle within conditions noted in FAILURE RECORDS data. Using scan tool, read SPECIFIC DTC while operating vehicle. Continue operating vehicle until DTC P0171 test runs. If scan tool displays DTC P0171 FAILED THIS IGN, go to next step. If scan tool does not display DTC P0171 FAILED THIS IGN, see «DIAGNOSTIC AIDS»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p0135-p0204) .
Check vacuum hoses for splits, kinks and proper routing. If a problem is found, repair as necessary. After repairs, go to step 22 . If no problem is found, go to next step.
Check PCV valve for proper installation. If a problem is found, repair as necessary. After repairs, go to step 22 . If no problem is found, go to next step.
Check throttle body inlet screen for blockage or foreign objects which may partially block airflow sample through MAF sensor. If a problem is found, repair as necessary. After repairs, go to step 22 . If no problem is found, go to next step.
Start engine. If high or unsteady idle condition exists, go to next step. If Idle is okay, go to step 11 .
Using scan tool, read IDLE AIR CONTROL (IAC) value. If value is greater than 5 counts, go to step 11 . If value is not greater than 5 counts, go to next step.
Check throttle body, intake manifold, and EGR valve for vacuum leaks. If a problem is found, repair as necessary. After repairs, go to step 22 . If no problem is found, go to next step.
Check IAC valve for proper operation. If a problem is found, repair as necessary. After repairs, go to step 22 . If no problem is found, go to next step.
Check for fuel contamination. If fuel is contaminated, repair condition causing contamination. After repairs, go to step 22 . If fuel is okay, go to next step.
Check PCM injector, power and sensor grounds for clean and tight connection, and for proper location. If a problem is found, repair as necessary. After repairs, go to step 22 . If no problem is found, go to next step.
Disconnect MAF sensor harness connector. Operate vehicle in closed loop mode while monitoring scan tool ST FUEL TRIM. If ST FUEL TRIM decreases to about zero percent, go to step 21 . If ST FUEL TRIM does not decrease to about zero percent, go to next step.
Check fuel pressure. See BASIC FUEL SYSTEM CHECKS in appropriate BASIC DIAGNOSTIC PROCEDURES article. If a problem is found, repair as necessary. After repairs, go to step 22 . If no problem is found, go to next step.
Perform EVAP system check. See EMISSION SYSTEMS & SUB-SYSTEMS in appropriate SYSTEM & COMPONENT TESTING article. If a problem is found, repair as necessary. After repairs, go to step 22 . If no problem is found, go to next step.
Check intake manifold, injector "O" rings, EGR adapter, EGR valve, and EGR feed pipes for vacuum leaks. If a problem is found, repair as necessary. After repairs, go to step 22 . If no problem is found, go to next step.
Check exhaust system for corrosion, loose or missing hardware. If a problem is found, repair as necessary. After repairs, go to step 22 . If no problem is found, go to next step.
Perform INJECTOR BALANCE TEST. See FUEL SYSTEM in appropriate SYSTEM & COMPONENT TESTING article. If a problem is found, repair as necessary. After repairs, go to step 22 . If no problem is found, go to next step.
Ensure HO2S is installed securely, and connector and harness are not contacting exhaust manifold or ignition wires. If a problem is found, repair as necessary. After repairs, go to step 22 . If no problem is found, see «DIAGNOSTIC AIDS»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p0135-p0204) .
Replace MAF sensor. After repairs, go to next step.
Using scan tool, read and record FAILURE RECORDS data, and clear DTCs. Operate vehicle within conditions noted in FAILURE RECORDS data. Using scan tool, select SPECIFIC DTC INFO for DTC P0171. If scan tool displays DTC P0171 FAILED THIS IGN, go to step 2 . If scan tool does not display DTC P0171 FAILED THIS IGN, system is okay.

Ensure HO2S wiring is routed correctly and not contacting exhaust system. Check for faulty PCM-to-engine ground connections. Check fuel pressure. Check fuel injector operation. Check for vacuum and exhaust leaks. Disconnect MAF sensor connector and see if lean condition is corrected. If lean condition is corrected, replace MAF sensor.

Check for fuel contamination. Check for faulty connections or damaged harness. If connections and harness appear okay, observe scan tool HO2S 1 display while moving all related harness and connectors. A change in scan tool display indicates fault location.

PCM reads HO2S signal voltage and adjusts fuel delivery based on this voltage. A change made to fuel delivery is indicated by Long Term (LT) and Short Term (ST) fuel trim values.

For duplication of DTC, ensure

No EVAP system, VSS, EST, misfire, fuel injector circuit, O2, CKP, CMP, TP, MAF, MAP, ECT or IAT sensor DTCs are set.
No ECT, EGR, HO2S, IAT, MAF, MAP or TP sensor DTCs set.
Engine coolant temperature is 68-230°F (20-110°C).
Intake air temperature is 0-158°F (-18-70°C).
MAF is 15-85 kPa.
Throttle angle is steady and less than 90 percent.
Vehicle speed is less than 82 MPH.
Engine speed is 600-4000 RPM.
BARO greater than 70 kPa.
Airflow is 3-150 gm/s.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-introduction__on-board-diagnostic-obd-system-check) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
If any other DTCs are set, diagnose affected DTCs before proceeding. If no other DTCs are set, go to next step.
Operate vehicle in closed loop mode while using scan tool to read LT and ST FUEL TRIM values. If values are greater than +15, go to step 5 . If values are not as specified, go to next step.
Using scan tool, read and record FAILURE RECORDS data. Clear DTCs and operate vehicle within conditions noted in FAILURE RECORDS data. Using scan tool, read SPECIFIC DTC while operating vehicle. Continue operating vehicle until DTC P0171 test runs. If scan tool displays DTC P0171 FAILED THIS IGN, go to next step. If scan tool does not display DTC P0171 FAILED THIS IGN, see «DIAGNOSTIC AIDS»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p0135-p0204) .
Check vacuum hoses for splits, kinks and proper routing. Repair as necessary. After repairs, go to step 23 . If no problem is found, go to next step.
Check PCV valve for proper installation. Repair as necessary. After repairs, go to step 23 . If no problem is found, go to next step.
Check throttle body inlet screen for blockage or foreign objects which may partially block airflow sample through MAF sensor. Repair as necessary. After repairs, go to step 23 . If no problem is found, go to next step.
Start engine. If high or unsteady idle condition exists, go to next step. If Idle is okay, go to step 11 .
Using scan tool, read IDLE AIR CONTROL (IAC) value. If value is greater than 5 counts, go to step 11 . If value is 5 counts or less, go to next step.
Check throttle body, intake manifold, and EGR valve for vacuum leaks. Repair as necessary. After repairs, go to step 23 . If no problem is found, go to next step.
Check IAC valve for proper operation. Repair as necessary. After repairs, go to step 23 . If no problem is found, go to next step.
Check for fuel contamination. If fuel is contaminated, repair condition causing contamination. After repairs, go to step 23 . If fuel is okay, go to next step.
Check PCM injector, power and sensor grounds for clean and tight connection, and for proper location. Repair as necessary. After repairs, go to step 23 . If no problem is found, go to next step.
Perform EVAP system check. See EMISSION SYSTEMS & SUB-SYSTEMS in appropriate SYSTEM & COMPONENT TESTING article. Repair as necessary. After repairs, go to step 23 . If no problem is found, go to next step.
Check fuel pressure. See BASIC FUEL SYSTEM CHECKS in BASIC DIAGNOSTIC PROCEDURES article. If a problem is found, repair as necessary. After repairs, go to step 23 . If no problem is found, go to next step.
Check intake manifold, injector "O" rings, EGR adapter, EGR valve, and EGR feed pipes for vacuum leaks. Repair as necessary. After repairs, go to step 23 . If no problem is found, go to next step.
Check exhaust system for corrosion, loose or missing hardware. Repair as necessary. After repairs, go to step 23 . If no problem is found, go to next step.
Disconnect MAF sensor harness connector. Operate vehicle in closed loop mode while monitoring scan tool ST FUEL TRIM. If ST FUEL TRIM decreases to about zero, go to step 21 . If ST FUEL TRIM does not decrease to about zero, go to next step.
Perform INJECTOR BALANCE TEST. See FUEL SYSTEM in appropriate SYSTEM & COMPONENT TESTING article. Repair as necessary. After repairs, go to step 23 . If no problem is found, go to next step.
Ensure HO2S is installed securely, and connector and harness are not contacting exhaust manifold or ignition wires. Repair as necessary. After repairs, go to step 23 . If no problem is found, see «DIAGNOSTIC AIDS»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p0135-p0204) .
Check MAF sensor screen for damage or obstruction. If a problem is found, go to next step. If no problem is found, go to step 23 .
Replace MAF sensor. After repairs, go to next step.
Using scan tool, read and record FAILURE RECORDS data, and clear DTCs. Operate vehicle within conditions noted in FAILURE RECORDS data. Using scan tool, select SPECIFIC DTC INFO for DTC P0171. If scan tool displays DTC P0171 FAILED THIS IGN, go to step 2 . If scan tool does not display DTC P0171 FAILED THIS IGN, system is okay.

DTC P0171: FUEL TRIM SYSTEM LEAN-BANK 1 (4.0L "G" BODY & 4.6L "E" & "K" BODIES)

Note. For circuit reference, see appropriate wiring diagram in WIRING DIAGRAMS article.

PCM monitors the HO2S signal voltage and adjusts fuel delivery based on signal voltage when system is in "closed loop". A change made to fuel delivery is indicated by the long and short term fuel trim values which can be monitored with a scan tool. Ideal fuel trim is about zero percent. If HO2S signal is indicating a lean condition, PCM will add fuel, resulting in a fuel trim greater than zero percent (100 percent maximum lean). If a rich condition is detected, fuel trim values will be less than zero percent (-99 percent maximum rich), indicating that PCM is reducing the amount of fuel delivered. If an excessive lean condition is detected, DTC P0171 will set.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-introduction__on-board-diagnostic-obd-system-check) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Using scan tool, check if any other DTCs are present. If other DTCs are present, diagnose affected DTCs first. If no other DTCs are present, go to next step.
Start and warm engine until coolant temperature reaches 185°F (85°C) or greater. Using scan tool, monitor LONG TERM BN. 1 and SHRT. TERM BN. 1 status. If either value is less than 95-98 percent, go to next step. If either value is not less than 95-98 percent, go to step 5 .
Using FREEZE FRAME data, note conditions under which the was DTC set. Clear DTC and operate vehicle under the conditions that set DTC. Using scan tool, select NOT RUN SCC and TEST FAIL SCC to verify that this diagnostic test runs while duplicating test conditions. If this diagnostic test ran and failed this ignition cycle, go to next step. If this diagnostic test did not run or did not fail in this ignition cycle, see «DIAGNOSTIC AIDS»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p0135-p0204) .
If DTC P0174 is also present, go to next step. If DTC P0174 is not present, go to step 7 .
Check vacuum hoses for splits, kinks and proper routing. Check throttle body, air induction system after MAF sensor, intake manifold, PCV and EGR valve for vacuum leaks. Check for contaminated fuel. Ensure PCM grounds are lean and tight. Check for mechanical failure. Repair as necessary. After repairs, go to step 8 . If system is okay or no problem is found, see «DIAGNOSTIC AIDS»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p0135-p0204) .
Inspect bank 1 for exhaust leaks, missing or loose exhaust hardware. Ensure HO2S is securely installed and wiring harness is not touching exhaust or ignition wires. Check for vacuum leaks that will only affect bank 1. Check for mechanical failure. If problem is found, go to next step. If system is okay or if no problem is found, see «DIAGNOSTIC AIDS»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p0135-p0204) .
Repair as necessary. After repairs, verify for proper operation of component(s).

If scan tool indicated that test ran and passed, fault is not present. If scan tool indicated that the test did not run, ensure that all the test conditions were met.

DTC P0171: FUEL TRIM SYSTEM LEAN-BANK 1 (4.3L, 5.0L, 5.7L & 7.4L "C", "G", "K", "L", "M", "P", "S" & "T" SERIES)

Note. For circuit reference, see appropriate wiring diagram in WIRING DIAGRAMS article.

A "closed loop" air/fuel metering system is utilized for driveability, fuel economy and emission control. While in closed loop, VCM monitors oxygen sensor signal voltage and adjusts fuel delivery based on signal voltage. A change in fuel delivery can be monitored using a scan tool and is indicated by Long Term (LT) and Short Term (ST) fuel trim values. Ideal fuel trim is about 128. If a lean condition is present, VCM will increase fuel, resulting in a fuel trim value greater than 128. If a rich condition is present, VCM will reduce fuel, resulting in a fuel trim value less than 128. DTC P0171 will set if an excessively lean condition is detected.

For duplication of DTC, ensure

No misfire, EVAP system, VSS, system voltage, ECT, EGR, HO2S, IAT, MAF, MAP or TP sensor DTCs are set.
Throttle position is less than 70 percent.
Engine speed is 575-4000 RPM.
BARO is greater than 70 kPa.
ECT is 167-237°F (75-114°C).
MAP is 22-85 kPa.
IAT is 46-169°F (-8 to 76°C).
MAF is 3-85 gm/s.
Vehicle speed is less than 85 MPH.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-introduction__on-board-diagnostic-obd-system-check) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Start engine and let idle in closed loop. Using scan tool, monitor LONG TERM FT BN 1 display. If value is greater than 20 percent, go to step 4 . If value is not greater than 20 percent, go to next step.
Turn ignition on, with engine off. Using scan tool, read and record FAILURE RECORDS data. Turn ignition off for 15 seconds. Start engine and operate vehicle within conditions for this DTC to set, and as close to conditions noted in FAILURE RECORDS data as possible. Using scan tool, read SPECIFIC DTC while operating vehicle. Continue operating vehicle until DTC P0171 test runs. If scan tool displays DTC P0171 FAILED THIS IGN, go to next step. If scan tool does not display DTC P0171 FAILED THIS IGN, see «DIAGNOSTIC AIDS»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p0135-p0204) .
If DTC P0174 is also set, go to next step. If DTC P0174 is not set, go to step 6 .
Check exhaust system for leaks, restriction in fuel filter, and vacuum leaks in air induction system after MAF sensor. Check vacuum hoses for splits, kinks and proper routing. Check throttle body, intake manifold, and EGR valve for vacuum leaks. Check IAC, if high or unsteady idle condition exists. Check crankcase ventilation valve, spring and "O" ring for proper installation. Check AIR system for proper operation (if equipped). Check for fuel contamination. Check for good VCM and sensor grounds. If any of these items isolate problem or require repair, go to step 10 . If all items are okay, go to step 7 .
Check exhaust system for leaks at bank 1. Check bank 1 HO2S 1 for proper installation. Ensure HO2S 1 harness and connector are not contacting exhaust system or secondary ignition wires. Check for vacuum leaks that may effect bank 1 HO2S 1. If any of these items isolate problem or require repair, go to step 10 . If all items are okay, go to next step.
Connect a fuel pressure gauge to fuel rail fitting. Turn ignition off for 10 seconds. Turn A/C off. Turn ignition on. Fuel pump should run for about 2 seconds. It may be necessary to cycle ignition more than once to obtain maximum pressure. Note pressure with pump running. On CSI models, pressure should be 60-66 psi (4.2-4.8 kg/cm 2 ). On SFI models, pressure should be 55-60 psi (3.9-4.2 kg/cm 2 ). On all models, when pump stops, pressure may vary slightly, but should hold steady. If pressure is as specified, go to next step. If pressure is not as specified, go to step 13 .
Start engine. Allow engine to idle at normal operating temperature. If fuel pressure is 55-60 psi (3.9-4.2 kg/cm 2 ), go to next step. If fuel pressure is not as specified, go to step 13 .
Perform injector balance test. See appropriate SYSTEM & COMPONENT TESTING article. If a problem is found, go to step 11 . If no problem is found, go to step 14 .
Repair components as necessary. Using scan tool, reset fuel trim. Operate vehicle in closed loop while monitoring LONG TERM FT BN 1 display. If value decreases to less than 20 percent, go to step 12 . If value does not decrease to less than 20 percent, go to step 7 .
Replace faulty fuel injector. Using scan tool, reset fuel trim. Operate vehicle in closed loop while monitoring LONG TERM FT BN 1 display. If value decreases to less than 20 percent, go to next step. If value does not decrease to less than 20 percent, go to step 7 .
Lean condition is not present at this time. If driveability symptoms are still present, see appropriate TROUBLE SHOOTING - NO CODES article. If no driveability symptoms are present, go to step 14 .
Diagnose fuel system. See appropriate BASIC DIAGNOSTIC PROCEDURES article. After repairs, go to next step.
Using scan tool, clear DTCs. Start and warm engine to normal operating temperature. Select DTC, SPECIFIC, and then enter this DTC. Operate vehicle within the conditions for setting this DTC. If scan tool indicates that this test ran and passed, go to next step. If scan tool does not indicate that this test ran and passed, go to step 2 .
Using scan tool, select CAPTURE INFO, REVIEW INFO function. If any undiagnosed DTCs are displayed, go to applicable DTC test. If no undiagnosed DTCs are displayed, system is okay.

If problem can not be isolated, monitor LT fuel trim value while operating vehicle under various load conditions. A condition that causes DTC P0300 may also result in DTC P0171 setting. Also, an extreme lean condition that may cause DTC P0171 to set may result in P0300 setting due to misfire at idle. If cause for DTC P0171 cannot be determined and DTC P0300 is also set, go to DTC P0300.

DTC P0171: FUEL TRIM SYSTEM LEAN-BANK 1 (4.8L, 5.3L & 6.0L "C" & "K" SERIES & 5.7L "F" & "Y" BODIES)

Note. For circuit reference, see appropriate wiring diagram in WIRING DIAGRAMS article.

PCM monitors oxygen sensor signal voltage and adjusts fuel delivery based on signal voltage. A change made to fuel delivery is indicated by long and short term fuel trim values.

Short term fuel trim values change rapidly in response to HO2S signal voltages. These changes fine tune engine fueling. Long term fuel trim values changes in response to trends in short term fuel trim. Long term fuel trim makes coarse adjustments to fueling in order to re-center and restore control to short term fuel trim. Long term and short term fuel trim can be monitored by use of scan tool.

Ideal fuel trim value is about zero percent. A positive fuel trim indicates that PCM is adding fuel to compensate for a lean condition. A negative fuel trim indicates that PCM is reducing amount of fuel to compensate for rich condition. DTC will set if PCM detects an excessively rich or lean condition.

For duplication of DTC, ensure

DTCs P0101, P0102, P0103, P0107, P0108, P0112, P0113, P0117, P0118, P0121, P0122, P0123, P0125, P0300, P0335, P0336, P0351-P0358, P0401, P0404, P0405, P0410, P0412, P0418, P0443, P0500, P0502, P0503, P1111, P1112, P1258, P1404, P1415 or P1416 are not set.
Engine coolant temperature is 120-239°F (60-115°C).
BARO is greater than 74 kPa.
MAF is 5-90 gm/s.
MAP is 26-90 kPa.
IAT is -4-194°F (-20-90°C).
Engine speed is 400-3000 RPM.
TP sensor angle is less than 90 percent.
Vehicle speed is less than 85 MPH.
Fuel level is greater than 10 percent.
PCM detects average long term fuel trim cell values are more than a predetermined threshold.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-introduction__on-board-diagnostic-obd-system-check) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Start and warm engine to normal operating temperature. Ensure system is in "closed loop". Using scan tool, select FUEL TRIM DATA LIST and monitor LT FT BN 1. If LT FT is less than 23 percent, go to next step. If values are not as specified, go to step 4 .
Turn ignition on, with engine off. Using scan tool, review FREEZE FRAME and/or FAILURE RECORDS data and note parameters. Turn ignition off for about 15 seconds. Start engine and operate vehicle within conditions required for this diagnostic to run, and as close to conditions recorded in FREEZE FRAME/FAILURE RECORDS as possible. Select DTC function then enter DTC P0171. If scan tool indicates that this test failed this ignition, go to next step. If scan tool does not indicate that this test failed this ignition, see «DIAGNOSTIC AIDS»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p0135-p0204) .
If DTC P0174 is also present, go to next step. If DTC P0174 is not present, go to step 6 .
Check vacuum hoses for splits, kinks and proper routing. MAF sensor, air induction system, throttle body, intake manifold, PCV system and EGR valve for vacuum leaks. Check for fuel contamination. Check for good PCM and sensor grounds. Check engine mechanical condition. Repair as necessary. After repairs, go to step 7 . If engine mechanical repairs are not necessary, diagnose fuel system. See appropriate SYSTEM & COMPONENT TESTING article.
Check bank 1 for exhaust leaks or loose exhaust hardware. Ensure oxygen sensor is properly installed. Check vacuum leaks that will affect bank 1 only. Check engine mechanical condition. After repairs, go to next step. If repairs are not necessary, diagnose fuel system. See appropriate SYSTEM & COMPONENT TESTING article.
Repair or replace any faulty items. After repairs, go to next step.
Using scan tool, clear DTCs. Start and warm engine to normal operating temperature. Select DTC, SPECIFIC, and then enter DTC P0171. Operate vehicle within conditions that set this DTC. If scan tool indicates that this test ran and passed, go to next step. If scan tool does not indicate that this test ran and passed, go to step 2 .
Using scan tool, select CAPTURE INFO, REVIEW INFO function. If any undiagnosed DTCs are displayed, diagnose affected DTCs. If no undiagnosed DTCs are displayed, system is okay.

If DTC P0171 cannot be duplicated, problem could have been caused by engine running out of fuel. A fuel delivery malfunction will cause DTC to set. Check all items that can cause a lean condition.

DTC will set if the averaged long term idle and cruise fuel trim cells are 101 and the current short term fuel trim cell is less than 128 for 3 seconds when PCM is using the non-purge long term fuel trim cells, system is in closed loop, coolant temperature is 140-239°F (60-115°C), airflow is 2-80 gm/s, MAP at 3-12 psi (.2-.8 kg/cm 2 ), RPM at 500-4000 RPM, TP is less than 75 percent open, BARO at greater than 10 psi (.7 kg/cm 2 ), IAT between -22°F (-30°C) to 176°F (80°C), vehicle speed less than 75 MPH and no ECT, MAP, IAT, TP sensor, VSS, EVAP canister purge, front O2S DTCs or DTC P0125 not present. Fuel control system is continuously checked when these conditions have been met.

A rich condition can be caused by fuel pressure too high, leaking fuel injectors, vacuum leak around MAP sensor grommet, oxygen sensor contamination or a restricted exhaust or air intake.

If the front O2S and the rear HO2S voltage reading is greater than 600 mV all the time, the oxygen sensors are probably not at fault.

DTC P0172: FUEL TRIM SYSTEM RICH (2.2L "J" BODY, 2.2L "S" SERIES & 2.4L "J" & "N" BODIES)

Note. For circuit reference, see appropriate wiring diagram in WIRING DIAGRAMS article.

A fuel trim value greater than 128 indicates that PCM is adding fuel to compensate for a lean condition. A fuel trim value less than 128 indicates that PCM is reducing amount of fuel to compensate for rich condition. DTC will set if PCM detects an excessively rich condition.

For duplication of DTC, ensure

DTCs P0106, P0107, P0108, P0112, P0113, P0117, P0118, P0121, P0122, P0123, P0125, P0131, P0132, P0133, P0134, P0200, P0300, P0301, P0302, P0303, P0304, P0325, P0335, P0341, P0342, P0401, P0404, P0405, P0502, P0503, P0506, P0507, P0601, P0602, P1404, P1133 or P1441 are not set.
IAT is -13-175°F (-25-115°C).
ECT is 140-239°F (60-115°C).
Vehicle speed is less than 70 MPH.
Engine speed is 750-3400 RPM.
Fuel trim index is less than 80.
EVAP purge is not occurring.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-introduction__on-board-diagnostic-obd-system-check) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
If any other DTCs are set, diagnose DTCs as necessary before proceeding. If no other DTCs are set, go to next step.
Start and warm engine to normal operating temperature. Ensure system is in closed loop. Using scan tool, select FUEL TRIM INDEX. If fuel trim index is less than 80 (2.2L) or 75 (2.4L), go to step 5 . If fuel trim index is not less than 80 (2.2L) or 75 (2.4L), go to next step.
Turn ignition on, with engine off. Using scan tool, review FREEZE FRAME data and note parameters. Start engine and operate vehicle within conditions required for setting this DTC, and as close to conditions recorded in FREEZE FRAME as possible. If fuel trim index is less than 80 (2.2L) or 75 (2.4L), go to step 21 . If fuel trim index is not less than 80 (2.2L) or 75 (2.4L), go to next step.
Turn ignition off. Check air filter. Replace filter as necessary. After repairs, go to step 21 . If air filter is okay, go to next step.
Check for collapsed or restricted air intake duct. Repair as necessary. After repairs, go to step 21 . If air intake duct is okay, go to next step.
Inspect throttle body inlet from damage of foreign objects that may partially block airflow. Repair as necessary. After repairs, go to step 21 . If no repair is necessary, go to next step.
Inspect throttle body bore, throttle plate and IAC passages for coking and foreign objects. Repair as necessary. After repairs, go to step 21 . If no repair is necessary, go to next step.
Start engine. Ensure all accessories are off. Note idle condition. If idle is low or unstable, go to next step. If idle is okay, go to step 12 .
Using scan tool, check IAC count. If IAC count is less than 100, go to step 12 . If IAC count is not less than 100, go to next step.
Disconnect MAP sensor harness connector. Start and warm engine to normal operating temperature. Ensure system is in closed loop. Using scan tool, select FUEL TRIM INDEX display. If fuel trim index is greater than 80 (2.2L) or 60 (2.4L), go to step 20 . If fuel trim index is not greater than 80 (2.2L) or 60 (2.4L), go to next step.
Go to DTC P0506 or P0507 to check IAC valve performance. Repair as necessary. After repairs, go to step 21 . If IAC valve is okay, go to next step.
Disconnect fuel pressure regulator vacuum hose. Check vacuum hose for presence of fuel. If fuel is present, replace fuel pressure regulator. After repairs, go to step 21 . If fuel pressure regulator is okay, go to next step.
Turn ignition on, with engine off. Using scan tool, monitor THROT POSITION display while slowly depressing accelerator pedal. If reading increases steadily from minimum voltage to maximum voltage at wide open throttle, go to next step. If reading does not increase steadily from minimum voltage to maximum voltage, go to step 19 .
Diagnose fuel system. See appropriate BASIC DIAGNOSTIC PROCEDURES article. Repair fuel system as necessary. After repairs, go to step 21 . If fuel system is okay, go to next step.
Check fuel evaporation system for proper operation. Ensure canister purge solenoid is functioning properly. See appropriate SYSTEM & COMPONENT TESTING article. Repair as necessary. After repairs, go to step 21 . If fuel evaporation system is functioning properly, go to next step.
Perform injector balance test. See appropriate SYSTEM & COMPONENT TESTING article. Repair as necessary. After repairs, go to step 21 . If no problems are found, go to next step.
Remove and inspect O2S 1 for silicone contamination. If contamination exists, a powdery White deposit on portion of sensor exposed to exhaust system will be present. If silicone contamination is present, locate and repair source of contamination. Replace O2S 1. After repairs, go to step 21 . If no contamination exists, see «DIAGNOSTIC AIDS»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p0135-p0204) .
Check TP sensor mounting screws. Tighten or replace screws as necessary. If mounting screws are okay, replace TP sensor. After repairs, go to step 21 .
Replace MAP sensor. After repairs, go to next step.
Using scan tool, clear DTCs. Start engine and allow it to idle. Ensure engine is at normal operating temperature. Operate vehicle within conditions required for setting this DTC. Select SPECIFIC DTC function, and then enter DTC P0172. If scan tool indicates that this test ran and passed, go to next step. If scan tool does not indicate that this test ran and passed, go to step 2 .
If any other DTCs are set, diagnose DTCs as necessary. If no other DTCs are set, system is okay.

Disconnect and inspect PCM harness connector. Inspect for damaged pins, corrosion and loose wires. Check oxygen sensor wiring harness for intermittent. An intermittent problem can be caused by misrouted harness, rubbed-through wire insulation or broken wire inside insulation. DO NOT attempt to repair damaged oxygen sensor connector or wiring. If damage is detected, replace oxygen sensor.

DTC P0172: FUEL TRIM SYSTEM RICH-BANK 1 (3.0L "V" BODY)

Note. For circuit reference, see appropriate wiring diagram in WIRING DIAGRAMS article.

For duplication of DTC, ensure ECM detects fuel trim values less than -550 milliseconds for additive fuel trim or less than -21 percent for multiplicative fuel trim.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-introduction__on-board-diagnostic-obd-system-check) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
If any other DTCs are set, except DTCs P0172 and P0175, proceed to that DTC before proceeding with this DTC. If no other DTCs are set, start engine and run to normal operating temperature. Ensure fuel system is in closed loop. Using scan tool, monitor short term and long term fuel trim for bank 1. If both parameters are not less than -95 on scan tool, go to step 4 . If both parameters are less than -95 on scan tool, go to next step.
Turn ignition on, with engine off. Review FREEZE FRAME data for this DTC and note parameters. Clear DTCs. Turn ignition off for 15 seconds. Operate vehicle as close to conditions recorded in FREEZE FRAME as possible. Check for DTCs. If DTC P0172 is set, go to next step. If DTC P0172 is not set, see «DIAGNOSTIC AIDS»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p0135-p0204) .
If DTC P0175 is also set, go to next step. If DTC P0175 is not set, go to step 6 .
Inspect for collapsed air intake duct. Ensure air filter is clean and not restricted. Ensure MAF sensor is installed in proper direction and no foreign objects are blocking inlet screen. Inspect for fuel in fuel pressure regulator hose. Repair components as necessary. After repairs, go step 8 . If all components are okay, diagnose fuel system malfunction. See appropriate BASIC DIAGNOSTIC PROCEDURES article.
Inspect fuel injectors on bank 1 for leaks. Repair as necessary. After repairs, go to step 8 . If fuel injectors are okay, go to next step.
Replace faulty HO2S. After repairs, go to next step.
Using scan tool, clear DTCs. Turn ignition off for 15 seconds. Start engine and operate vehicle as close to conditions recorded in FREEZE FRAME as possible. Check for DTCs. If DTC P0172 is set, go to step 2 . If DTC P0172 is not set, go to next step.
If other DTCs were present during OBD system check and have not been diagnosed, go to applicable DTC. If no other DTCs are present, system is okay.

Condition is intermittent. See appropriate TROUBLE SHOOTING - NO CODES article for diagnosis.

If HO2S signals are indicating a lean condition, the PCM will add fuel, resulting in fuel trim values greater than zero percent. If a rich condition is detected, fuel trim values will be less than zero percent, indicating that PCM is reducing amount of fuel delivered.

For duplication of DTC, ensure

No active misfire, fuel injector circuit, EVAP system, fuel trim, TP, IAT, MAP, EGR, ECT, MAF or CKP sensor DTCs are set.
ECT is 68-230°F (20-110°C).
IAT is 0-149°F (-18-65°C).
TP sensor angle is less than 90 percent.
Vehicle speed is less than 75 MPH (82 MPH on 3.4L).
On 3.1L, engine speed is 550-5000 RPM.
On 3.4L, engine speed is 600-4000 RPM.
Long Term (LT) fuel trim is about +16 percent.
Short Term (ST) fuel trim is about +20 percent.
BARO is greater than 70 kPa.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-introduction__on-board-diagnostic-obd-system-check) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
If any other DTCs are set, diagnose DTCs as necessary before proceeding. If no other DTCs are set, go to next step.
Start and warm engine to normal operating temperature. Ensure system is in closed loop. Using scan tool, select ENG 1 data list. Observe L.T. FUEL TRIM and S.T. FUEL TRIM. If L.T. FUEL TRIM is about -16 percent and S.T. FUEL TRIM is about -11 percent, go to step 5 . If fuel trim is not as specified, go to next step.
Using scan tool, clear DTCs. Turn ignition on, with engine off. Using scan tool, review FREEZE FRAME data and note parameters. Start engine and operate vehicle within conditions required for setting this DTC, and as close to conditions recorded in FREEZE FRAME as possible. Monitor SPECIFIC DTC info for DTC P0171 until DTC P0171 test runs. If scan tool indicates FAILED THIS IGN, go to next step. If scan tool does not indicate FAILED THIS IGN, see «DIAGNOSTIC AIDS»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p0135-p0204) .
Inspect air filter element. Replace as necessary. After repairs, go to step 21 . If air filter element is okay, go to next step.
Check for collapsed or restricted air intake duct. Repair as necessary. After repairs, go to step 21 . If air duct is okay, go to next step.
Inspect throttle body inlet screen for damage or blockage. Repair as necessary. After repairs, go to step 21 . If inlet screen is okay, go to next step.
Start engine and check idle quality. If idle is high or rough, go to next step. If idle is okay, go to step 11 .
Allow engine to idle. Using scan tool, observe IDLE AIR CONTROL display. If counts are greater than 100, go to step 11 . If counts are not greater than 100, go to next step.
Turn ignition off. Inspect throttle body bore, throttle plate and IAC passages for coking and foreign objects. Repair as necessary. After repairs, go to step 21 . If no problem is found, go to next step.
Check Idle Air Control (IAC) valve operation. See appropriate SYSTEM & COMPONENT TESTING article. Repair as necessary. After repairs, go to step 21 . If IAC valve is functioning properly, go to step 13 .
Disconnect vacuum hose from fuel pressure regulator and check hose for presence of fuel. If fuel is present, replace fuel pressure regulator. After repairs, go to step 21 . If fuel pressure regulator is okay, go to next step.
Turn ignition on. Monitor TP angle display on scan tool while slowly depressing accelerator pedal. If TP angle display increase steadily from 0-100 percent (wide-open throttle), go to next step. If TP angle display does not increase as specified, go to step 19 .
Disconnect MAF sensor harness connector. Start engine and allow it to idle. Ensure system is in closed loop. Using scan tool, observe ST FUEL TRIM and LT FUEL TRIM display. If both values change to about zero percent, go to step 21 . If one or both values do not change to about zero percent, go to next step.
Diagnose fuel system. See appropriate BASIC DIAGNOSTIC PROCEDURES article. Repair fuel system as necessary. After repairs, go to step 21 . If fuel system is okay, go to next step.
Check fuel evaporation system for proper operation. Ensure canister purge solenoid is functioning properly. See appropriate SYSTEM & COMPONENT TESTING article. Repair as necessary. After repairs, go to step 21 . If fuel evaporation system is functioning properly, go to next step.
Perform injector balance test. See FUEL SYSTEM in appropriate SYSTEM & COMPONENT TESTING article. Repair as necessary. After repairs, go to step 21 . If no problems were found, go to next step.
Visually and physically inspect HO2S 1 for silicon contamination (White powdery deposits). If contamination is evident, replace sensor. After repairs, go to step 21 . If sensor is okay, see «DIAGNOSTIC AIDS»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p0135-p0204) .
Check TP sensor mounting screws. Tighten or replace screws as necessary. If screws are okay, replace TP sensor. After repairs, go to step 21 .
Replace MAF sensor. After repairs, go to next step.
Using scan tool, clear DTCs. Turn ignition on, with engine off. Using scan tool, review FREEZE FRAME data and note parameters. Start engine and operate vehicle within conditions required for setting this DTC, and as close to conditions recorded in FREEZE FRAME as possible. Monitor SPECIFIC DTC info until DTC P0171 test runs. If scan tool indicates FAILED THIS IGN, go to step 2 . If scan tool does not indicate FAILED THIS IGN, system is okay.

PCM reads HO2S signal voltage and adjusts fuel delivery based on this voltage. A change made to fuel delivery is indicated by Long Term (LT) and Short Term (ST) fuel trim values.

Ideal fuel trim value is about zero. Fuel trim value is greater than zero indicates that PCM is adding fuel to compensate for a lean condition. Fuel trim less than zero indicates that PCM is reducing amount of fuel to compensate for rich condition. DTC will set if PCM detects an excessively rich or lean condition.

For duplication of DTCs, ensure

No EVAP system, misfire, fuel injector circuit, IAC, ECT, EGR, HO2S, IAT, MAF, MAP or TP sensor DTCs are set.
Engine speed is 500-4000 RPM.
ECT is 68-230°F (20-110°C).
IAT is 0-104°F (-18-40°C).
BARO is greater than 10.7 psi (0.75 kg/cm 2 ).
MAP is 2.6-12.8 psi (0.18-0.90 kg/cm 2 )
TP angle is less than 90 percent.
MAF is 9-180 grams per second.
Long term fuel trim is near maximum authority (-25).
Short term fuel trim is near maximum authority (-11).
Vehicle speed is less than 70 MPH.
Conditions are met in FUEL TRIM CELLS 0, 1, 2, 6, and/or 7.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-introduction__on-board-diagnostic-obd-system-check) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
If any other DTCs are set, diagnose affected DTCs before proceeding. If no other DTCs are set, go to next step.
Operate vehicle in closed loop mode while using scan tool to read LT and ST FUEL TRIM values. If LT FUEL TRIM and ST FUEL TRIM value is about -10, go to step 5 . If values are not as specified, go to next step.
Using scan tool, read and record FAILURE RECORDS data. Clear DTCs and operate vehicle within conditions noted in FAILURE RECORDS data. Using scan tool, read SPECIFIC DTC while operating vehicle. Continue operating vehicle until DTC P0172 test runs. If scan tool displays DTC P0172 FAILED THIS IGN, go to next step. If scan tool does not display DTC P0172 FAILED THIS IGN, see «DIAGNOSTIC AIDS»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p0135-p0204) .
Check air filter element condition. Replace air filter element if necessary. After repairs, go to step 21 . If air filter element is okay, go to next step.
Check air intake duct for being collapsed or restricted. Repair as necessary. After repairs, go to step 21 . If no problem is found, go to next step.
Check throttle body inlet screen for blockage or foreign objects which may partially block airflow sample through MAF sensor. Repair as necessary. After repairs, go to step 21 . If no problem is found, go to next step.
Start engine. If high or unsteady idle condition exists, go to next step. If Idle is okay, go to step 11 .
Using scan tool, read IDLE AIR CONTROL (IAC) value. If value is less than 100 counts, go to step 11 . If value is not less than 100 counts, go to next step.
Turn ignition off. Check throttle body bore, throttle plate and IAC passages for coking and foreign objects. Repair as necessary. After repairs, go to step 21 . If no problem is found, go to next step.
Check IAC valve for proper operation. Repair as necessary. After repairs, go to step 21 . If no problem is found, go to next step.
Disconnect vacuum hose from fuel pressure regulator and check it for presence of fuel. If fuel is present, replace fuel pressure regulator. After repairs, go to step 21 . If no fuel is present, go to next step.
Turn ignition on, engine off. Using scan tool, read TP ANGLE while slowly depressing accelerator pedal. If TP ANGLE increases steadily from zero percent at closed throttle to 100 percent at wide open throttle, go to next step. If TP ANGLE does not increase as specified, to step 19 .
Disconnect MAF sensor harness connector. Operate vehicle in closed loop mode while monitoring scan tool LT and ST FUEL TRIM. If both fuel trim values decrease to about zero, go to step 20 . If fuel trim values do not decrease to about zero, go to next step.
Check fuel pressure. See BASIC FUEL SYSTEM CHECKS in appropriate BASIC DIAGNOSTIC PROCEDURES article. Repair as necessary. After repairs, go to step 21 . If no problem is found, go to next step.
Perform EVAP system check. See EMISSION SYSTEMS & SUB-SYSTEMS in appropriate SYSTEM & COMPONENT TESTING article. Repair as necessary. After repairs, go to step 21 . If no problem is found, go to next step.
Perform fuel injector balance test. See FUEL SYSTEM in appropriate SYSTEM & COMPONENT TESTING article. Repair as necessary. After repairs, go to step 21 . If no problem is found, go to next step.
Remove HO2S 1 and check it for silicone (powdery white deposit) contamination. Replace HO2S 1 if contaminated. After repairs, go to step 21 . If HO2S 1 is not contaminated, see «DIAGNOSTIC AIDS»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p0135-p0204) .
Check and tighten TP sensor mounting screws. If mounting screws are tight, replace TP sensor. After repairs, go to step 21 .
Replace MAF sensor. After repairs, go to next step.
Using scan tool, read and record FAILURE RECORDS data, and clear DTCs. Operate vehicle within conditions noted in FAILURE RECORDS data. Using scan tool, select SPECIFIC DTC INFO for DTC P0172. If scan tool displays DTC P0172 FAILED THIS IGN, go to step 2 . If scan tool does not display DTC P0172 FAILED THIS IGN, system is okay.

Check fuel pressure. Check fuel injector operation. Disconnect MAF sensor connector and see if rich condition is corrected. If rich condition is corrected, replace MAF sensor.

Check for faulty TP sensor operation. Check for faulty connections or damaged harness. If connections and harness appear okay, observe scan tool HO2S 1 display while moving all related harness and connectors. A change in scan tool display indicates fault location.

PCM reads HO2S signal voltage and adjusts fuel delivery based on this voltage. A change made to fuel delivery is indicated by Long Term (LT) and Short Term (ST) fuel trim values.

Ideal fuel trim value is about zero. Fuel trim value greater than zero indicates that PCM is adding fuel to compensate for a lean condition. Fuel trim less than zero indicates that PCM is reducing amount of fuel to compensate for rich condition. DTC will set if PCM detects an excessively rich or lean condition.

For duplication of DTC, ensure

No misfire, HO2S, EVAP system, IAC, fuel injector circuit, ECT, EGR, IAT, MAF, MAP or TP sensor DTCs are set.
Engine speed is 500-4000 RPM.
ECT is 68-230°F (20-110°C).
IAT is 0-104°F (-18-40°C).
BARO is greater than 10.7 psi (0.75 kg/cm 2 ).
MAP is 2.6-12.8 psi (0.18-0.90 kg/cm 2 ).
TP angle is less than 90 percent.
MAF is 9-180 grams per second.
Long term fuel trim is near maximum authority (-23).
Short term fuel trim is near maximum authority (-11).
Vehicle speed is less than 70 MPH.
Conditions are met in FUEL TRIM CELLS 0, 1, 2, 6, and/or 7.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-introduction__on-board-diagnostic-obd-system-check) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
If any other DTCs (except P0172 and P0175) are set, diagnose affected DTCs before proceeding. If no other DTCs are set, go to next step.
Operate vehicle in closed loop mode while using scan tool to read BANK 1 LT and BANK 1 ST FUEL TRIM values. If BANK 1 LT FUEL TRIM value is about -23 and BANK 1 ST FUEL TRIM value is about -11, go to step 5 . If values are not as specified, go to next step.
Using scan tool, read and record FAILURE RECORDS data. Clear DTCs and operate vehicle within conditions noted in FAILURE RECORDS data. Using scan tool, read SPECIFIC DTC while operating vehicle. Continue operating vehicle until DTC P0172 test runs. If scan tool displays DTC P0172 FAILED THIS IGN, go to next step. If scan tool does not display DTC P0172 FAILED THIS IGN, see «DIAGNOSTIC AIDS»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p0135-p0204) .
If DTC P0175 is also set, go to next step. If DTC P0175 is not set, go to step 18 .
Check air filter element condition. Replace air filter element if necessary. After repairs, go to step 22 . If air filter element is okay, go to next step.
Check air intake duct for being collapsed or restricted. Repair as necessary. After repairs, go to step 22 . If no problem is found, go to next step.
Check throttle body inlet screen for blockage or foreign objects which may partially block airflow sample through MAF sensor. Repair as necessary. After repairs, go to step 22 . If no problem is found, go to next step.
Start engine. If high or unsteady idle condition exists, go to next step. If idle is okay, go to step 12 .
Using scan tool, read IDLE AIR CONTROL (IAC) value. If value is less than 100 counts, go to step 12 . If value is not less than 100 counts, go to next step.
Turn ignition off. Check throttle body bore, throttle plate and IAC passages for coking and foreign objects. Repair as necessary. After repairs, go to step 22 . If no problem is found, go to next step.
Check IAC valve for proper operation. Repair as necessary. After repairs, go to step 22 . If no problem is found, go to next step.
Disconnect vacuum hose from fuel pressure regulator and check it for presence of fuel. If fuel is present, replace fuel pressure regulator. After repairs, go to step 22 . If no fuel is present, go to next step.
Turn ignition on, engine off. Using scan tool, read TP ANGLE while slowly depressing accelerator pedal. If TP ANGLE increases steadily from zero percent at closed throttle to 100 percent at wide open throttle, go to next step. If TP ANGLE does not increase as specified, to step 20 .
Disconnect MAF sensor harness connector. Operate vehicle in closed loop mode while monitoring scan tool BANK 1 LT and ST FUEL TRIM. If both fuel trim values decrease to about zero, go to step 21 . If fuel trim values do not decrease to about zero, go to next step.
Check fuel pressure. See BASIC FUEL SYSTEM CHECKS in appropriate BASIC DIAGNOSTIC PROCEDURES article. Repair as necessary. After repairs, go to step 22 . If no problem is found, go to next step.
Perform EVAP system check. See EMISSION SYSTEMS & SUB-SYSTEMS in appropriate SYSTEM & COMPONENT TESTING article. Repair as necessary. After repairs, go to step 22 . If no problem is found, go to next step.
Perform injector balance test. See FUEL SYSTEM in appropriate SYSTEM & COMPONENT TESTING article. Repair as necessary. After repairs, go to step 22 . If no problem is found, go to next step.
Remove HO2S 1 and HO2S 2, and check them for silicone (powdery white deposit) contamination. Replace HO2S if contaminated. After repairs, go to step 22 . If HO2S is not contaminated, see «DIAGNOSTIC AIDS»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p0135-p0204) .
Check and tighten TP sensor mounting screws. If mounting screws are tight, replace TP sensor. After repairs, go to step 22 .
Replace MAF sensor. After repairs, go to next step.
Using scan tool, read and record FAILURE RECORDS data, and clear DTCs. Operate vehicle within conditions noted in FAILURE RECORDS data. Using scan tool, select SPECIFIC DTC INFO for DTC P0172. If scan tool displays DTC P0172 FAILED THIS IGN, go to step 2 . If scan tool does not display DTC P0172 FAILED THIS IGN, system is okay.

Check fuel pressure. Check fuel injector operation. Disconnect MAF sensor harness connector and see if rich condition is corrected. If rich condition is corrected, replace MAF sensor.

DTC P0172: FUEL TRIM SYSTEM RICH-BANK 1 (4.0L "G" BODY & 4.6L "E" & "K" BODIES)

Note. For circuit reference, see appropriate wiring diagram in WIRING DIAGRAMS article.

PCM monitors the HO2S signal voltage and adjusts fuel delivery based on signal voltage when system in "closed loop". A change made to fuel delivery is indicated by the long and short term fuel trim values which can be monitored with a scan tool. Ideal fuel trim is about zero percent. If HO2S signal is indicating a lean condition, PCM will add fuel, resulting in a fuel trim greater than zero percent (100 percent maximum lean). If a rich condition is detected, fuel trim values will be less than zero percent (-99 percent maximum rich), indicating that PCM is reducing the amount of fuel delivered. If an excessive rich condition is detected, DTC P0172 will set.

For duplication of DTC, ensure

DTCs P0101-P0103, P0106-P0108, P0121, P0122, P0131-P0134, P0137, P0138, P0140, P0143, P0144, P0146, P0151, P0154, P0163, P0201-P0208, P0300, P0325, P0327, P0340, P0401, P0506, P0507, P0562, P1121, P1133, P1153, P1154, P1441, P1508 or P1509 are not set.
System is in closed loop.
ECT is 185-221°F (85-105°C).
BARO is greater than 70.8 kPa.
MAF is 3-200 grams per second.
MAP is 27-103 kPa.
IAT is -40-304°F (-40-151°C).
Engine speed is 400-3000 RPM.
TP angle is less than 19.8 percent.
Vehicle speed is less than 70 MPH.
EVAP canister purge tank is not full.
Fuel trim is enabled.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-introduction__on-board-diagnostic-obd-system-check) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Using scan tool, check if any other DTCs are present. If other DTCs are present, diagnose affected DTCs first. If no other DTCs are present, go to next step.
Warm engine until coolant temperature reaches 185°F (85°C) or greater. Using scan tool, monitor LONG TERM BN. 1 and SHRT. TERM BN. 1 status. If either displayed value is less than -95 or -98 percent, go to next step. If neither displayed value is less than -95 or -98 percent, go to step 5 .
Using FREEZE FRAME data, note conditions under which the DTC was set. Clear DTC and operate vehicle under the conditions that set DTC. Using scan tool, select NOT RUN SCC and TEST FAIL SCC to verify that this diagnostic test runs while duplicating test conditions. If this diagnostic test ran and failed this ignition cycle, go to next step. If this diagnostic test did not run or did not fail in this ignition cycle, see «DIAGNOSTIC AIDS»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p0135-p0204) .
If DTC P0175 is also present, go to next step. If DTC P0175 is not present, go to step 7 .
Check for collapsed air intake duct, restricted air filter, improperly installed MAF sensor or for foreign objects blocking MAF sensor screen. Check for fuel in pressure regulator vacuum hose. If a problem is found, go to step 8 . If no problem is found, see «DIAGNOSTIC AIDS»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p0135-p0204) .
Inspect for leaking fuel injectors at bank 1. Repair as necessary. If fuel injectors are okay, go to step 9 .
Repair or replace any faulty items.
Replace HO2S 2.

If scan tool indicated that test ran and passed, fault is not present. If scan tool indicated that the test did not run, ensure that all the test conditions were met.

DTC P0172: FUEL TRIM SYSTEM RICH-BANK 1 (4.3L, 5.0L, 5.7L & 7.4L "C", "G", "K", "L", "M", "P", "S" & "T" SERIES)

Note. For circuit reference, see appropriate wiring diagram in WIRING DIAGRAMS article.

A "closed loop" air/fuel metering system is utilized for driveability, fuel economy and emission control. While in closed loop, VCM monitors oxygen sensor signal voltage and adjusts fuel delivery based on signal voltage. A change in fuel delivery can be monitored using a scan tool and is indicated by Long Term (LT) and Short Term (ST) fuel trim values. Ideal fuel trim is about 128. If a lean condition is present, VCM will increase fuel, resulting in a fuel trim value greater than 128. If a rich condition is present, VCM will reduce fuel, resulting in a fuel trim value less than 128. DTC P0172 will set if an excessively rich condition is detected.

For duplication of DTC, ensure

No misfire, VSS, system voltage, ECT, EGR, EVAP, HO2S, IAC, IAT, MAF, MAP or TP sensor DTCs are set.
Throttle position is less than 69.9 percent.
Engine speed is 575-4000 RPM.
BARO is greater than 70 kPa.
ECT is 167-237°F (75-114°C).
MAP is 22-85 kPa.
IAT is 46-169°F (-8.3-76°C).
MAF is 3-85 gm/s.
Vehicle speed is less than 85 MPH.
Average short term fuel trim is less than 115.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-introduction__on-board-diagnostic-obd-system-check) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Check for collapsed or restricted air intake duct or plugged air filter. Check throttle body for coking or objects blocking IAC passage, if a low or unsteady idle is being experienced. Check fuel pressure regulator for proper operation. See appropriate BASIC DIAGNOSTIC PROCEDURES article. Check TP sensor for loose or missing mounting bolts. Monitor TP sensor voltage with scan tool while slowly opening throttle. Voltage should increase steadily and evenly from closed throttle voltage (0.2 volt) to wide open throttle voltage (4.5 volts). If voltage is not as specified, replace TP sensor. If a problem is found, go to step 8 . If no problem is found, go to next step.
Connect a fuel pressure gauge to fuel rail fitting. Turn ignition off for 10 seconds. Turn A/C off. Turn ignition on. Fuel pump should run for about 2 seconds. It may be necessary to cycle ignition more than once to obtain maximum pressure. Note pressure with pump running. On CSI models, pressure should be 60-66 psi (4.2-4.6 kg/cm 2 ). On SFI models, pressure should be 55-60 psi (3.9-4.2 kg/cm 2 ). On all models, when pump stops, pressure may slightly vary, but should hold steady. If pressure is as specified, go to next step. If pressure is not as specified, go to step 11 .
Perform injector balance test. See FUEL SYSTEM in appropriate SYSTEM & COMPONENT TESTING article. If a problem is found, go to step 9 . If no problem is found, go to next step.
Remove HO2S and inspect for silicone contamination (a white powdery deposit on portion of sensor exposed to exhaust stream). If contamination is found, go to step 12 . If contamination is not found, go to next step.
Perform canister purge solenoid check. See EMISSION SYSTEMS & SUB-SYSTEMS in appropriate SYSTEM & COMPONENT TESTING article. If a problem is found, go to next step. If no problem is found, see «DIAGNOSTIC AIDS»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p0135-p0204) .
Repair EVAP system. Install scan tool. Operate vehicle in closed loop while monitoring LT and ST fuel trim values. LT fuel trim value should increase to greater than 100. ST fuel trim value should increase to greater than 94. If values are as specified, go to step 10 . If values are not as specified, see «DIAGNOSTIC AIDS»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p0135-p0204) .
Repair problem as necessary. Operate vehicle in closed loop while monitoring LT and ST fuel trim values. LT fuel trim value should increase to greater than 100. ST fuel trim value should increase to greater than 94. If values are as specified, go to step 10 . If values are not as specified, go to step 3 .
Replace fuel injector. Operate vehicle in closed loop while monitoring LT and ST fuel trim values. LT fuel trim value should increase to greater than 100. ST fuel trim value should increase to greater than 94. If values are as specified, go to next step. If values are not as specified, go to step 5 .
Rich condition is not present. If driveability symptoms are still present, see appropriate TROUBLE SHOOTING - NO CODES article for diagnosis. If no symptoms are present, go to step 13 .
Diagnose fuel system. See appropriate BASIC DIAGNOSTIC PROCEDURES article. After repairs, go to step 13 .
Replace HO2S. After repairs, go to next step.
Using scan tool, clear DTCs. Start and warm engine to normal operating temperature. Select DTC, SPECIFIC, and then enter this DTC. Operate vehicle within the conditions for setting this DTC. If scan tool indicates that this test ran and passed, go to next step. If scan tool does not indicate that this test ran and passed, go to step 2 .
Using scan tool, select CAPTURE INFO, REVIEW INFO function. If any undiagnosed DTCs are displayed, go to applicable DTC test. If no undiagnosed DTCs are displayed, system is okay.

If problem can not be isolated during diagnostic procedures, monitor LT fuel trim value while operating vehicle under various load conditions. A condition that causes DTC P0300 may also result in DTC P0172 setting. Also, an extreme rich condition that may cause DTC P0172 to set may result in P0300 setting due to misfire at idle. If cause for DTC P0172 can not be determined and DTC P0300 is also set, go to DTC P0300.

PCM monitors oxygen sensor signal voltage and adjusts fuel delivery based on signal voltage. A change made to fuel delivery is indicated by long and short term fuel trim values.

Ideal fuel trim value is about zero percent. A positive fuel trim indicates that PCM is adding fuel to compensate for a lean condition. A negative fuel trim indicates that PCM is reducing amount of fuel to compensate for rich condition. DTC P0172 will set if PCM detects an excessively rich condition.

For duplication of DTC, ensure

DTCs P0101-P0103, P0107, P0108, P0112, P0113, P0117, P0118, P0121-P0123, P0125, P0200, P0300, P0335, P0336, P0351-P0358, P0401, P0404, P0405, P0410, P0412, P0418, P0443, P0500, P0502, P0503, P1111, P1112, P1258, P1404, P1415 or P1416 are not set.
Engine coolant temperature between 120-239°F (60-115°C).
BARO is greater than 74 kPa.
MAF is 5-90 gm/s.
MAP is 26-90 kPa.
IAT is -4-194°F (-20-90°C).
Engine speed is 400-3000 RPM.
TP sensor angle is less than 90 percent.
Vehicle speed is less than 85 MPH.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-introduction__on-board-diagnostic-obd-system-check) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Start and warm engine to normal operating temperature. Ensure system is in "closed loop" operation. Using scan tool, select FUEL TRIM DATA LIST and monitor LT FT BN 1. If LT FT is greater than -13 percent, go to next step. If LT FT is not greater than -13 percent, go to step 4 .
Turn ignition on, with engine off. Using scan tool, review FREEZE FRAME and/or FAILURE RECORDS data and note parameters. Turn ignition off for about 15 seconds. Start engine and operate vehicle within conditions required for this diagnostic to run, and as close to conditions recorded in FREEZE FRAME/FAILURE RECORDS as possible. Select DTC function, and then enter DTC P0172. If scan tool indicates that this test failed this ignition, go to next step. If scan tool does not indicate that this test failed this ignition, see «DIAGNOSTIC AIDS»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p0135-p0204) .
If DTC P0175 is also present, go to next step. If DTC P0175 is not present, go to step 6 .
Check for collapsed air intake duct, restricted fuel filter, improperly installed MAF sensor, foreign objects in MAF sensor inlet or for fuel in fuel regulator hose. Repair as necessary. After repairs, go to step 7 . If components are okay, or repair is not necessary, diagnose fuel system. See appropriate BASIC DIAGNOSTIC PROCEDURES article.
Check for leaking fuel injectors in bank 1. Repair or replace as necessary. After repairs, go to step 9 . If injectors are okay, go to step 8 .
Replace or repair affected components. After repairs, go to step 9 .
Replace faulty HO2S. After repairs, go to next step.
Using scan tool, clear DTCs. Start and warm engine to normal operating temperature. Select DTC, SPECIFIC, and then enter DTC P0172. Operate vehicle within conditions that set DTC. If scan tool indicates that this test ran and passed, go to next step. If scan tool does not indicate that this test ran and passed, go to step 2 .
Using scan tool, select CAPTURE INFO, REVIEW INFO function. If any undiagnosed DTCs are displayed, diagnose affected DTCs. If no undiagnosed DTCs are displayed, system is okay.

For intermittent problem, see appropriate TROUBLE SHOOTING - NO CODES article.

DTC P0174: FUEL TRIM SYSTEM LEAN-BANK 2 (3.0L "V" BODY)

Note. For circuit reference, see appropriate wiring diagram in WIRING DIAGRAMS article.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-introduction__on-board-diagnostic-obd-system-check) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
If any other DTCs are set, except DTCs P0171 and P0174, proceed to that DTC before proceeding with this DTC. If no other DTCs are set, warm engine to normal operating temperature. Ensure fuel system is in closed loop. Using scan tool, monitor short term and long term fuel trim for bank 2. If both parameters are less than 95 percent, go to next step. If both parameters are not less than 95 percent, go to step 4 .
Turn ignition on, with engine off. Review FREEZE FRAME data for this DTC and note parameters. Clear DTCs. Turn ignition off for 15 seconds. Operate vehicle as close to conditions recorded in FREEZE FRAME as possible. Check for DTCs. If DTC P0174 is set, go to next step. If DTC P0174 is not set, see «DIAGNOSTIC AIDS»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p0135-p0204) .
If DTC P0171 is also set, go to next step. If DTC P0171 is not set, go to step 6 .
Inspect for collapsed air intake duct. Ensure air filter is clean and not restricted. Ensure MAF sensor is installed in proper direction and no foreign objects are blocking inlet screen. Inspect for fuel in fuel pressure regulator hose. Repair components as necessary. After repairs, go step 7 . If all components are okay, diagnose fuel system malfunction. See BASIC FUEL SYSTEM CHECKS in appropriate BASIC DIAGNOSTIC PROCEDURES article.
Inspect bank 2 for exhaust or vacuum leaks, or bank 2 HO2S 1 for proper installation. Repair as necessary. After repairs, go to next step. If no problems are found, diagnose fuel system. See BASIC FUEL SYSTEM CHECKS in appropriate BASIC DIAGNOSTIC PROCEDURES article.
Using scan tool, clear DTCs. Turn ignition off for 15 seconds. Operate vehicle as close to conditions recorded in FREEZE FRAME as possible. Check for DTCs. If DTC P0174 is set, go to step 2 . If DTC P0174 is not set, go to next step.
If other DTCs were present during OBD system check and have not been diagnosed, go to applicable DTC. If no other DTCs are present, system is okay.

If DTC P0174 cannot be duplicated, vehicle must have run out of fuel. Check for low fuel pressure, causing lean condition. Check for water contamination. See appropriate TROUBLE SHOOTING - NO CODES article for diagnosis.

DTC P0174: FUEL TRIM SYSTEM LEAN-BANK 2 (3.8L "F" BODY)

Note. For circuit reference, see appropriate wiring diagram in WIRING DIAGRAMS article.

PCM reads HO2S signal voltage and adjusts fuel delivery based on this voltage. A change made to fuel delivery is indicated by Long Term (LT) and Short Term (ST) fuel trim values.

Ideal fuel trim value is about zero. Fuel trim value more than zero indicates that PCM is adding fuel to compensate for a lean condition. Fuel trim less than zero indicates that PCM is reducing amount of fuel to compensate for rich condition. DTC P0174 will set if PCM detects an excessively lean condition.

For duplication of DTC, ensure

No IAC, EVAP system, misfire, ECT, EGR, HO2S, IAT, MAF, MAP or TP sensor DTCs are set.
Engine speed is 500-4000 RPM.
ECT is 68-230°F (20-110°C).
IAT is 0-104°F (-18-40°C).
BARO is greater than 10.7 psi (0.75 kg/cm 2 ).
TP angle is less than 90 percent.
MAF is 9-180 grams per second.
Long term fuel trim is near maximum authority (16).
Short term fuel trim is near maximum authority (20).
Vehicle speed is less than 70 MPH.
Conditions are met in fuel trim cells 0, 1, 2, 6, and/or 7.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-introduction__on-board-diagnostic-obd-system-check) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
If any other DTCs (except P0171 and P0174) are set, diagnose affected DTCs before proceeding. If no other DTCs are set, go to next step.
Operate vehicle in closed loop mode while using scan tool to read BANK 2 LT and ST fuel trim values. If LT fuel trim value is about 16 and ST fuel trim value is about 20, go to step 5 . If values are not as specified, go to next step.
Using scan tool, read and record FAILURE RECORDS data. Clear DTCs and operate vehicle within conditions noted in FAILURE RECORDS data. Using scan tool, read SPECIFIC DTC while operating vehicle. Continue operating vehicle until DTC P0174 test runs. If scan tool displays DTC P0174 FAILED THIS IGN, go to next step. If scan tool does not display DTC P0174 FAILED THIS IGN, see «DIAGNOSTIC AIDS»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p0135-p0204) .
If DTC P0171 is also set, go to DTC P0171. If DTC is not set, go to next step.
Perform EVAP system check. See EMISSION SYSTEMS & SUB-SYSTEMS in appropriate SYSTEM & COMPONENT TESTING article. Repair as necessary. After repairs, go to step 11 . If no problem is found, go to next step.
Check intake manifold, injector "O" rings, EGR adapter, EGR valve, and EGR feed pipes for vacuum leaks. Repair as necessary. After repairs, go to step 11 . If no problem is found, go to next step.
Check exhaust system for corrosion, loose or missing hardware. Repair as necessary. After repairs, go to step 11 . If no problem is found, go to next step.
Perform injector balance test. See appropriate SYSTEM & COMPONENT TESTING article. Repair as necessary. After repairs, go to step 11 . If no problem is found, go to next step.
Ensure HO2S 2 is installed securely, and connector and harness are not contacting exhaust manifold or ignition wires. Repair as necessary. After repairs, go to next step. If no problem is found, see «DIAGNOSTIC AIDS»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p0135-p0204) .
Using scan tool, read and record FAILURE RECORDS data, and clear DTCs. Operate vehicle within conditions noted in FAILURE RECORDS data. Using scan tool, select SPECIFIC DTC INFO for DTC P0174. If scan tool displays DTC P0174 FAILED THIS IGN, go to step 2 . If scan tool does not display DTC P0174 FAILED THIS IGN, system is okay.

Check for fuel contamination. Check for faulty connections or damaged harness. If connections and harness appear okay, observe scan tool HO2S 2 display while moving all related harness and connectors. A change in scan tool display indicates fault location.

DTC P0174: FUEL TRIM SYSTEM LEAN-BANK 2 (4.0L "G" BODY & 4.6L "E" & "K" BODIES)

Note. For circuit reference, see appropriate wiring diagram in WIRING DIAGRAMS article.

PCM monitors the HO2S signal voltage and adjusts fuel delivery based on signal voltage when system in "closed loop". A change made to fuel delivery will be indicated by the long and short term fuel trim values which can be monitored with a scan tool. Ideal fuel trim is about zero percent. If HO2S signal is indicating a lean condition, PCM will add fuel, resulting in a fuel trim greater than zero percent (100 percent maximum lean). If rich condition is detected, fuel trim values will be less than zero percent (-99 percent maximum rich), indicating that PCM is reducing the amount of fuel delivered. If an excessive lean condition is detected, DTC P0174 will set.

For duplication of DTC, ensure

DTCs P0101-P0103, P0106-P0108, P0121, P0122, P0131-P0134, P0337, P0338, P0140, P0143, P0144, P0146, P0151, P0154, P0163, P0201-P0208, P0300, P0325, P0327, P0340, P0401, P0506, P0507, P0562, P1121, P1133, P1153, P1154, P1441, P1508 or P1509 are not set.
Closed loop is enabled.
Engine coolant temperature is 185-221°F (85-105°C).
BARO is greater than 70.8 kPa.
MAF is 3-200 gm/s.
MAP is 27-103.2 kPa.
IAT is -40-304°F (-40-151°C).
Engine speed is 400-3000 RPM.
TP sensor angle is less than 19.8 percent.
Vehicle speed is less than 70 MPH.
EVAP canister purge tank is not full.
Fuel trim is enabled.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-introduction__on-board-diagnostic-obd-system-check) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Using scan tool, check if any other DTCs are present. If other DTCs are present, diagnose affected DTCs first. If no other DTCs are present, go to next step.
Start and warm engine until coolant temperature reaches 185°F (85°C) or greater. Using scan tool, monitor LONG TERM BN. 1 and SHRT. TERM BN. 1 status. If either values are greater than 95-98 percent, go to next step. If either values are less than 95-98 percent, go to step 5 .
Using FREEZE FRAME data, note conditions under which the DTC set. Clear DTC and operate vehicle under the conditions that set DTC. Using scan tool, select NOT RUN SCC and TEST FAIL SCC to verify that this diagnostic test runs while duplicating test conditions. If this diagnostic test ran and failed this ignition cycle, go to next step. If this diagnostic test did not run or did not fail in this ignition cycle, see «DIAGNOSTIC AIDS»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p0135-p0204) .
If DTC P0171 is also present, go to next step. If DTC P0171 is not present, go to step 7 .
Check vacuum hoses for splits, kinks and proper routing. Check throttle body, air induction system after MAF sensor, intake manifold, PCV and EGR valve for vacuum leaks. Check for contaminated fuel. Ensure PCM grounds are lean and tight. Check for mechanical failure. Repair as necessary. After repairs, go to step 8 . If system is okay or no problem is found, see «DIAGNOSTIC AIDS»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p0135-p0204) .
Inspect bank 2 for exhaust leaks, missing or loose exhaust hardware. Ensure HO2S is securely installed and wiring harness is not touching exhaust or ignition wires. Check for vacuum leaks that will only affect bank 2. Check for mechanical failure. If problem is found, go to next step. If system is okay or no problem is found, see «DIAGNOSTIC AIDS»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p0135-p0204) .
Repair as necessary. After repairs, verify for proper operation of components.

If scan tool indicated that test ran and passed, fault is not present. If scan tool indicated that the test did not run, ensure that all the test conditions were met.

DTC P0174: FUEL TRIM SYSTEM LEAN-BANK 2 (4.3L, 5.0L, 5.7L & 7.4L "C", "G", "K", "L", "M", "P", "S" & "T" SERIES)

Note. For circuit reference, see appropriate wiring diagram in WIRING DIAGRAMS article.

A "closed loop" air/fuel metering system is utilized for driveability, fuel economy and emission control. While in closed loop, VCM monitors oxygen sensor signal voltage and adjusts fuel delivery based on signal voltage. A change in fuel delivery can be monitored using a scan tool and is indicated by Long Term (LT) and Short Term (ST) fuel trim values. Ideal fuel trim is about 128. If a lean condition is present, VCM will increase fuel, resulting in a fuel trim value greater than 128. If a rich condition is present, VCM will reduce fuel, resulting in a fuel trim value less than 128. DTC P0174 will set if an excessively lean condition is detected.

For duplication of DTC, ensure

No VSS, misfire, ECT, EGR, EVAP, HO2S, IAC, IAT, MAF, MAP or TP sensor DTCs are set.
Throttle position is less than 70 percent.
Engine speed is 575-4000 RPM.
BARO is greater than 70 kPa.
ECT is 167-237°F (75-114°C).
MAP is 22-85 kPa.
IAT is 46-169°F (-8.3-76°C).
MAF is 3-85 gm/s.
Vehicle speed is less than 85 MPH.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-introduction__on-board-diagnostic-obd-system-check) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Check for the following conditions: Exhaust system for corrosion, loose or missing hardware. HO2S is securely installed and pigtail is not contacting exhaust manifold or ignition wiring. Vacuum hoses for splits, kinks and proper connections. Throttle body, intake manifold and EGR for vacuum leaks. IAC, if a high or unsteady idle is being experienced. Crankcase ventilation valve, spring and "O" ring for proper installation. Fuel for excessive water, alcohol or other contaminants. VCM and sensor ground are clean, tight and in proper locations. If a problem is found, go to step 8 . If no problem is found, go to next step.
Connect a fuel pressure gauge to fuel rail fitting. Turn ignition off for 10 seconds. Turn A/C off. Turn ignition on. Fuel pump should run for about 2 seconds. It may be necessary to cycle ignition more than once to obtain maximum pressure. Note pressure with pump running. On CSI models, pressure should be 60-66 psi (4.2-4.6 kPa). On SFI models, pressure should be 55-60 psi (3.9-4.2 kPa). On all models, when pump stops, pressure may slightly vary, but should hold steady. If pressure is as specified, go to next step. If pressure is not as specified, go to step 11 .
Start and idle engine at normal operating temperature. If pressure decreases by 3-10 psi (.2-.7 kg/cm 2 ), go to next step. If pressure does not decrease by 3-10 psi (.2-.7 kg/cm 2 ), go to step 11 .
Perform injector balance test. See appropriate SYSTEM & COMPONENT TESTING article. If a problem is found, go to step 9 . If no problem is found, go to next step.
Perform canister purge solenoid check. See EMISSION SYSTEMS & SUB-SYSTEMS in appropriate SYSTEM & COMPONENT TESTING article. If a problem is found, go to next step. If no problem is found, see «DIAGNOSTIC AIDS»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p0135-p0204) .
Repair EVAP system. Install scan tool. Operate vehicle in closed loop while monitoring LT and ST fuel trim values. LT fuel trim value should decrease to less than 158. ST fuel trim value should decrease to less than 180. If values are as specified, go to step 10 . If values are not as specified, see «DIAGNOSTIC AIDS»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p0135-p0204) .
Repair problem as necessary. Operate vehicle in closed loop while monitoring LT and ST fuel trim values. LT fuel trim value should decrease to less than 158. ST fuel trim value should decrease to less than 180. If values are as specified, go to step 10 . If values are not as specified, go to step 3 .
Replace fuel injector. Operate vehicle in closed loop while monitoring LT and ST fuel trim values. LT fuel trim value should decrease to less than 158. ST fuel trim value should decrease to less than 180. If values are as specified, go to next step. If values are not as specified, go to step 6 .
Lean condition is not present. See appropriate TROUBLE SHOOTING - NO CODES article for diagnosis.
Diagnose fuel system. See appropriate BASIC DIAGNOSTIC PROCEDURES article. After repairs, go to next step.
Using scan tool, clear DTCs. Start and warm engine to normal operating temperature. Select DTC, SPECIFIC, and then enter this DTC. Operate vehicle within the conditions for setting this DTC. If scan tool indicates that this test ran and passed, go to next step. If scan tool does not indicate that this test ran and passed, repeat step 2 .
Using scan tool, select CAPTURE INFO, REVIEW INFO function. If any undiagnosed DTCs are displayed, go to applicable DTC test. If no undiagnosed DTCs are displayed, system is okay.

If problem can not be isolated during diagnostic procedures, monitor LT fuel trim value while operating vehicle under various load conditions. A condition that causes DTC P0300 may also result in DTC P0174 setting. Also, an extreme lean condition that may cause DTC P0174 to set may result in P0300 setting due to misfire at idle. If cause for DTC P0174 can not be determined and DTC P0300 is also set, go to DTC P0300.

DTC P0174: FUEL TRIM SYSTEM LEAN-BANK 2 (4.8L, 5.3L & 6.0L "C" & "K" SERIES & 5.7L "F" & "Y" BODIES)

Note. For circuit reference, see appropriate wiring diagram in WIRING DIAGRAMS article.

PCM monitors oxygen sensor signal voltage and adjusts fuel delivery based on signal voltage. A change made to fuel delivery is indicated by long and short term fuel trim values.

Ideal fuel trim value is about zero percent. A positive fuel trim indicates that PCM is adding fuel to compensate for a lean condition. A negative fuel trim indicates that PCM is reducing amount of fuel to compensate for a rich condition. DTC P0174 will set if PCM detects an excessively lean condition.

For duplication of DTC, ensure

DTCs P0101-P0103, P0107, P0108, P0112, P0113, P0117, P0118, P0121-P0123, P0125, P0200, P0300, P0335, P0336, P0351-P0358, P0401, P0404, P0405, P0410, P0412, P0418, P0443, P0500, P0502, P0503, P1111, P1112, P1258, P1404, P1415 or P1416 are not set.
Engine coolant temperature is 120-239°F (60-115°C).
BARO is greater than 74 kPa.
MAF is 5-90 gm/s.
MAP is 26-90 kPa.
IAT is -4-194°F (-20-90°C).
Engine speed is 400-3000 RPM.
TP sensor angle is less than 90 percent.
Vehicle speed is less than 85 MPH.
Fuel level is greater than 10 percent.
PCM detects average long term fuel trim cell values greater than a predetermined threshold.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-introduction__on-board-diagnostic-obd-system-check) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Start and warm engine to normal operating temperature. Ensure system is in "closed-loop". Using scan tool, select FUEL TRIM DATA LIST and monitor LT FT BN 2. If LT FT BN 2 is less than 23 percent, go to next step. If displayed value is not less than 23 percent, go to step 4 .
Turn ignition on, with engine off. Using scan tool, review FREEZE FRAME and/or FAILURE RECORDS data and note parameters. Turn ignition off for about 15 seconds. Start engine and operate vehicle within conditions required for this diagnostic to run, and as close to conditions recorded in FREEZE FRAME/FAILURE RECORDS as possible. Select DTC function, and then enter DTC P0174. If scan tool indicates that this test failed this ignition, go to next step. If scan tool does not indicate that this test failed this ignition, see «DIAGNOSTIC AIDS»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p0135-p0204) .
If DTC P0171 is also present, go to next step. If DTC P0171 is not present, go to step 6 .
Check vacuum hoses for splits, kinks and proper routing. Check for vacuum leaks at throttle body, intake manifold, EGR valve or MAF sensor. Check for fuel contamination. Check for engine mechanical failure. Repair problem as necessary. After repairs, go to step 7 . If problem is not found or repair is not necessary, diagnose fuel system. See appropriate SYSTEM & COMPONENT TESTING article.
Inspect bank 2 for exhaust leaks, missing or loose hardware. Check if bank 2 HO2S is installed properly and if connectors are secured. Check vacuum leaks that will only affect bank 1. Check engine mechanical condition. Repair problem as necessary. After repairs, go to next step. If problem is not found or repair is not necessary, diagnose fuel system. See appropriate SYSTEM & COMPONENT TESTING article.
Repair or replace affected faulty components. After repairs or replacement, go to next step.
Using scan tool, clear DTCs. Start and warm engine to normal operating temperature. Select DTC, SPECIFIC, and then enter DTC P0174. Operate vehicle within conditions for setting this DTC. If scan tool indicates that this test ran and passed, go to next step. If scan tool does not indicate that this test ran and passed, go to step 2 .
Using scan tool, select CAPTURE INFO, REVIEW INFO function. If any undiagnosed DTCs are displayed, go to applicable DTC test. If no undiagnosed DTCs are displayed, system is okay.

If DTC cannot be duplicated, DTC may have been set by engine running out of fuel. A fuel delivery malfunction will also cause DTC to set. Inspect related items that can cause a lean condition.

DTC P0175: FUEL TRIM SYSTEM RICH-BANK 2 (3.0L "V" BODY)

Note. For circuit reference, see appropriate wiring diagram in WIRING DIAGRAMS article.

To provide best possible combination of driveability, fuel economy and emission control, a closed loop air/fuel metering system is used. While in closed loop, ECM monitors heated oxygen sensor signal voltage and adjusts fuel delivery based on signal voltage. A change made in fuel delivery will be indicated by long and short term fuel trim values. Short term fuel trim values change rapidly in response to HO2S signal voltages. These changes fine tune engine fueling.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-introduction__on-board-diagnostic-obd-system-check) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
If any other DTCs are set, except DTCs P0172 and P0175, proceed to that DTC before proceeding with this DTC. If no other DTCs are set, warm engine to normal operating temperature. Ensure fuel system is in closed loop. Using scan tool, monitor short term and long term fuel trim for bank 2. If both parameters are less than -95 percent, go to step 4 . If both parameters are not less than -95 percent, go to next step.
Turn ignition on, with engine off. Review FREEZE FRAME data for this DTC and note parameters. Clear DTCs. Turn ignition off for 15 seconds. Operate vehicle as close to conditions recorded in FREEZE FRAME as possible. Check for DTCs. If DTC P0175 is set, go to next step. If DTC P0175 is not set, see «DIAGNOSTIC AIDS»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p0135-p0204) .
If DTC P0172 is also set, go to next step. If DTC P0172 is not set, go to step 6 .
Inspect for collapsed air intake duct. Ensure air filter is clean and not restricted. Ensure MAF sensor is installed in proper direction and no foreign objects are blocking inlet screen. Inspect for fuel in fuel pressure regulator hose. Repair components as necessary. After repairs, go step 8 . If all components are okay, diagnose fuel system malfunction. See BASIC FUEL SYSTEM CHECKS in appropriate BASIC DIAGNOSTIC PROCEDURES article.
Inspect bank 2 for leaks. Repair as necessary. After repairs, go to step 8 . If no problems are found, go to next step.
Replace faulty HO2S. After repairs, go to next step.
Using scan tool, clear DTCs. Turn ignition off for 15 seconds. Operate vehicle as close to conditions recorded in FREEZE FRAME as possible. Check for DTCs. If DTC P0175 is set, go to step 2 . If DTC P0175 is not set, go to next step.
If other DTCs were present during OBD system check and have not been diagnosed, go to applicable DTC. If no other DTCs are present, system is okay.

Problem is intermittent. See appropriate TROUBLE SHOOTING - NO CODES article for diagnosis.

DTC P0175: FUEL TRIM SYSTEM RICH-BANK 2 (3.8L "F" BODY)

Note. For circuit reference, see appropriate wiring diagram in WIRING DIAGRAMS article.

PCM reads HO2S signal voltage and adjust fuel delivery based on this voltage. A change made to fuel delivery is indicated by Long Term (LT) and Short Term (ST) fuel trim values.

Ideal fuel trim value is about zero. Fuel trim value more than zero indicates that PCM is adding fuel to compensate for a lean condition. Fuel trim less than zero indicates that PCM is reducing amount of fuel to compensate for rich condition. DTC will set if PCM detects an excessively rich or lean condition.

For duplication of DTC, ensure

No EVAP system, VSS, EST, misfire, fuel injector circuit, CKP, CMP, TP, MAF, O2, MAP, EGR, ECT or IAT sensor DTCs are set.
ECT is 68-230°F (20-110°C).
IAT is 0-158°F (-18-70°C).
MAP is 15-85 kPa.
TP sensor angle is less than 90 percent.
Vehicle speed is less than 82 MPH.
Engine speed is 600-4000 RPM.
BARO is greater than 70 kPa.
MAF is 3-150 grams per second.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-introduction__on-board-diagnostic-obd-system-check) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
If any other DTCs except P0172 and P0175 are set, diagnose affected DTCs before proceeding. If no other DTCs are set, operate vehicle in closed loop mode while using scan tool to read LT fuel trim value for bank 2. If value is greater than -18 percent, go to next step. If value is not greater than -18 percent, go to step 4 .
Using scan tool, read and record FAILURE RECORDS data. Clear DTCs and operate vehicle within conditions noted in FAILURE RECORDS data. Using scan tool, read SPECIFIC DTC while operating vehicle. Continue operating vehicle until DTC P0175 test runs. If scan tool displays DTC P0175 FAILED THIS IGN, go to next step. If scan tool does not display DTC P0175 FAILED THIS IGN, see «DIAGNOSTIC AIDS»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p0135-p0204) .
If DTC P0172 is also set, go to next step. If DTC P0172 is not set, go to step 6 .
Inspect for collapsed air intake duct. Ensure air filter is clean and not restricted. Ensure MAF sensor is installed in proper direction and no foreign objects are blocking inlet screen. Inspect for fuel in fuel pressure regulator hose. Repair components as necessary. After repairs, go step 7 . If all components are okay, diagnose fuel system malfunction. See BASIC FUEL SYSTEM CHECKS in appropriate BASIC DIAGNOSTIC PROCEDURES article.
Check for leaking fuel injectors on bank 2. If injectors are leaking, go to step 9 . If fuel injectors are not leaking, go to step 8 .
Repair or replace faulty system components as necessary. After repairs, go to step 9 .
Replace faulty HO2S. After repairs, go to next step.
Using scan tool, read and record FAILURE RECORDS data, and clear DTCs. Operate vehicle within conditions noted in FAILURE RECORDS data. Using scan tool, select SPECIFIC DTC INFO for DTC P0172. If scan tool displays DTC P0172 FAILED THIS IGN, go to step 2 . If scan tool does not display DTC P0172 FAILED THIS IGN, go to next step.
Using scan tool, select CAPTURE INFO, REVIEW INFO function. If any undiagnosed DTCs are displayed, go to applicable DTC test. If no undiagnosed DTCs are displayed, system is okay.

Check fuel pressure. Check fuel injector operation. Disconnect MAF sensor connector and see if rich condition is corrected. If rich condition is corrected, replace MAF sensor.

Check for faulty TP sensor operation. Check for faulty connections or damaged harness. If connections and harness appear okay, observe scan tool HO2S 2 display while moving all related harness and connectors. A change in scan tool display indicates fault location.

DTC P0175: FUEL TRIM SYSTEM RICH-BANK 2 (4.0L "G" BODY & 4.6L "E" & "K" BODIES)

Note. For circuit reference, see appropriate wiring diagram in WIRING DIAGRAMS article.

PCM monitors the HO2S signal voltage and adjust fuel delivery based on signal voltage when system in "closed loop". A change made to fuel delivery will be indicated by the long and short term fuel trim values which can be monitored with a scan tool. Ideal fuel trim is about zero percent. If HO2S signal is indicating a lean condition, PCM will add fuel, resulting in a fuel trim greater than zero percent (100 percent maximum lean). If rich condition is detected, fuel trim values will be less than zero percent (-99 percent maximum rich), indicating that PCM is reducing the amount of fuel delivered. If an excessive rich condition is detected, DTC P0175 will set.

For duplication of DTC, ensure

DTCs P0101-P0103, P0106-P0108, P0121, P0122, P0131-P0134, P0337, P0338, P0140, P0143, P0144, P0146, P0151, P0154, P0163, P0201-P0208, P0300, P0325, P0327, P0340, P0401, P0506, P0507, P0562, P1121, P1133, P1153, P1154, P1441, P1508 or P1509 are not set.
Closed loop is enabled.
Engine coolant temperature is 185-221°F (85-105°C).
BARO is greater than 70.8 kPa.
MAF is 3-200 gm/s.
MAP is 27-200 kPa.
IAT is -40-304°F (-40-151°C).
Engine speed is 400-3000 RPM.
TP sensor angle is less than 19.8 percent.
Vehicle speed is less than 70 MPH.
EVAP canister purge tank is not full.
Fuel trim is enabled.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-introduction__on-board-diagnostic-obd-system-check) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Using scan tool, check if any other DTCs are present. If other DTCs are present, diagnose affected DTCs first. If no other DTCs are present, go to next step.
Start an warm engine until coolant temperature reaches 185°F (85°C) or greater. Using scan tool, monitor LONG TERM BN. 1 and SHRT. TERM BN. 1 status. If either values are less than -95 or -98 percent, go to next step. If neither value is less than -95 or -98 percent, go to step 5 .
Using FREEZE FRAME data, note conditions under which the DTC set. Clear DTC and operate vehicle under the conditions that set DTC. Using scan tool, select NOT RUN SCC and TEST FAIL SCC to verify that this diagnostic test runs while duplicating test conditions. If this diagnostic test ran and failed this ignition cycle, go to next step. If this diagnostic test did not run or did not fail in this ignition cycle, see «DIAGNOSTIC AIDS»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p0135-p0204) .
If DTC P0172 is also present, go to next step. If DTC P0172 is not present, go to step 7 .
Check for collapsed air intake duct, restricted air filter, improperly installed MAF sensor or for foreign objects blocking MAF sensor screen. Check for fuel in pressure regulator vacuum hose. If a problem is found, go to step 8 . If no problems are found, diagnose fuel system. See BASIC FUEL SYSTEM CHECKS in appropriate BASIC DIAGNOSTIC PROCEDURES article.
Inspect for leaking fuel injectors at bank 2. Repair as necessary. If fuel injectors are okay, go to step 9 .
Repair or replace any faulty components.
Replace front HO2S.

If scan tool indicated that test ran and passed, fault is not present. If scan tool indicated that the test did not run, ensure that all the test conditions were met.

DTC P0175: FUEL TRIM SYSTEM RICH-BANK 2 (4.3L, 5.0L, 5.7L & 7.4L "C", "G", "K", "L", "M", "P", "S" & "T" SERIES)

Note. For circuit reference, see appropriate wiring diagram in WIRING DIAGRAMS article.

A "closed loop" air/fuel metering system is utilized for driveability, fuel economy and emission control. While in closed loop, VCM monitors oxygen sensor signal voltage and adjusts fuel delivery based on signal voltage. A change in fuel delivery can be monitored using a scan tool and is indicated by Long Term (LT) and Short Term (ST) fuel trim values. Ideal fuel trim is about 128. If a lean condition is present, VCM will increase fuel, resulting in a fuel trim value greater than 128. If a rich condition is present, VCM will reduce fuel, resulting in a fuel trim value less than 128. DTC P0175 will set if an excessively rich condition is detected.

For duplication of DTC, ensure

No VSS, misfire, EVAP system, ECT, EGR, HO2S, IAC, IAT, MAF, MAP or TP sensor DTCs are set.
Throttle position is less than 70 percent.
Engine speed is 575-4000 RPM.
BARO is greater than 70 kPa.
ECT is 167-237°F (75-114°C).
MAP is 22-85 kPa.
IAT is 46-169°F (-8.3-76°C).
MAF is 3-85 gm/s.
Vehicle speed is less than 85 MPH.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-introduction__on-board-diagnostic-obd-system-check) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Start engine and let idle in closed loop. Using scan tool, monitor LT fuel trim for bank 2. If value is less than -14 percent, go to next step. If value is not less than -14 percent, go to step 4 .
Turn ignition on, with engine off. Review FREEZE FRAME data for this DTC and note parameters. Clear DTCs. Turn ignition off for 15 seconds. Operate vehicle as close to conditions recorded in FREEZE FRAME as possible. Check for DTCs. If DTC P0175 is set, go to next step. If DTC P0175 is not set, see «DIAGNOSTIC AIDS»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p0135-p0204) .
Check for the following conditions: Air filter plugged or air intake duct collapsed or restricted. Proper MAF sensor installation and inlet screen condition. Throttle body coking or objects blocking IAC passage, if a low or unsteady idle is being experienced. HO2S 1, bank 2 connector and harness routing. Ensure harness does not contact exhaust system. Fuel pressure regulator for proper operation. See BASIC FUEL SYSTEM CHECKS in appropriate BASIC DIAGNOSTIC PROCEDURES article. Excessive fuel in crankcase. Change oil if necessary. If a problem is found, go to step 9 . If no problem is found, go to next step.
Connect a fuel pressure gauge to fuel rail fitting. Turn ignition off for 10 seconds. Turn A/C off. Turn ignition on. Fuel pump should run for about 2 seconds. It may be necessary to cycle ignition more than once to obtain maximum pressure. Note pressure with pump running. On CSI models, pressure should be 60-66 psi (4.2-4.6 kPa). On SFI models, pressure should be 55-60 psi (3.9-4.2 kPa). On all models, when pump stops, pressure may slightly vary, but should hold steady. If pressure is as specified, go to next step. If pressure is not as specified, go to step 12 .
Perform injector balance test. See appropriate SYSTEM & COMPONENT TESTING article. If a problem is found, go to step 10 . If no problem is found, go to next step.
Perform diagnostic procedures for DTC P1441. If a problem is found, go to next step. If no problem is found, see «DIAGNOSTIC AIDS»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p0135-p0204) .
Repair EVAP system. Start engine and let idle in closed loop. Using scan tool, monitor LT fuel trim for bank 2. If value is less than -14 percent, go to step 11 . If value is not less than -14 percent, go to step 4 .
Repair faulty item found in step 4) . Start engine and let idle in closed loop. Using scan tool, monitor LT fuel trim for bank 2. If value is less than -14 percent, go to step 11 . If value is not less than -14 percent, go to step 5 .
Replace faulty fuel injector. Start engine and let idle in closed loop. Using scan tool, monitor LT fuel trim for bank 2. If value is less than -14 percent, go to next step. If value is not less than -14 percent, go to step 5 .
Rich condition is not present at this time. If driveability symptoms are still present, see appropriate TROUBLE SHOOTING - NO CODES article for diagnosis. If no driveability symptoms are present, go to step 13 .
Diagnose fuel system. See BASIC FUEL SYSTEM CHECKS in appropriate BASIC DIAGNOSTIC PROCEDURES article. After repairs, go to next step.
Using scan tool, clear DTCs. Turn ignition off for 15 seconds. Operate vehicle as close to conditions recorded in FREEZE FRAME as possible. Check for DTCs. If DTC P0175 is set, go to step 2 . If DTC P0175 is not set, go to next step.
Using scan tool, select CAPTURE INFO, REVIEW INFO function.. If any undiagnosed DTCs are displayed, go to applicable DTC test. If no undiagnosed DTCs are displayed, system is okay.

If problem can not be isolated during diagnostic procedures, monitor LT fuel trim value while operating vehicle under various load conditions. A condition that causes DTC P0300 may also result in DTC P0175 setting. Also, an extreme rich condition that may cause DTC P0175 to set may result in P0300 setting due to misfire at idle. If cause for DTC P0175 cannot be determined and DTC P0300 is also set, go to DTC P0300.

DTC P0175: FUEL TRIM SYSTEM RICH-BANK 2 (4.8L, 5.3L & 6.0L "C" & "K" SERIES & 5.7L "F" & "Y" BODIES)

Note. For circuit reference, see appropriate wiring diagram in WIRING DIAGRAMS article.

PCM monitors oxygen sensor signal voltage and adjusts fuel delivery based on signal voltage. A change made to fuel delivery is indicated by long and short term fuel trim values.

Ideal fuel trim value is about zero percent. A positive fuel trim indicates that PCM is adding fuel to compensate for a lean condition. A negative fuel trim indicates that PCM is reducing amount of fuel to compensate for rich condition. DTC P0175 will set if PCM detects an excessively rich condition.

For duplication of DTC, ensure

DTCs P0101-P0103, P0107, P0108, P0112, P0113, P0117, P0118, P0121-P0123, P0125, P0200, P0300, P0335, P0336, P0351-P0358, P0401, P0404, P0405, P0410, P0412, P0418, P0443, P0500, P0502, P0503, P1111, P1112, P1258, P1404, P1415 or P1416 are not set.
Engine coolant temperature is 122-239°F (50-115°C).
Barometric pressure is greater than 74 kPa.
MAF is 5-90 gm/s.
MAP is 26-90 kPa.
IAT -4-194°F (-20-90°C).
Engine speed is 400-3000 RPM.
TP sensor angle is less than 90 percent.
Vehicle speed is less than 85 MPH.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-introduction__on-board-diagnostic-obd-system-check) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Warm engine to normal operating temperature. Ensure system is in closed loop. Using scan tool, select FUEL TRIM DATA LIST and monitor LF FT BN 2. If LT FT BN 2 displayed value is greater than -13 percent, go to next step. If displayed value is not greater than -13 percent, go to step 4 .
Turn ignition on, with engine off. Using scan tool, review FREEZE FRAME and/or FAILURE RECORDS data and note parameters. Turn ignition off for about 15 seconds. Start engine and operate vehicle within conditions required for this diagnostic to run, and as close to conditions recorded in FREEZE FRAME/FAILURE RECORDS as possible. Select DTC function, and then enter DTC P0175. If scan tool indicates that this test failed this ignition, go to next step. If scan tool does not indicate that this test failed this ignition, see «DIAGNOSTIC AIDS»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p0135-p0204) .
If DTC P0172 is also present, go to next step. If DTC P0172 is not present, go to step 6 .
Check for collapsed air intake duck, restricted air filter, improperly mounted MAF sensor, foreign objects blocking inlet screen or for fuel in pressure regulator hose. Repair as necessary. After repairs, go to step 7 . If problem is not found or repairs are not necessary, diagnose fuel system. See BASIC FUEL SYSTEM CHECKS in appropriate SYSTEM & COMPONENT TESTING article.
Check for leaking fuel injectors on bank 2. If fuel injectors are leaking, go to step 9 . If fuel injectors are okay, go to step 8 .
Repair or replace affected components. After repairs, go to step 9 .
Replace faulty HO2S. After repairs, go to next step.
Using scan tool, clear DTCs. Start and warm engine to normal operating temperature. Select DTC, SPECIFIC, and then enter DTC P0175. Operate vehicle within conditions for setting this DTC. If scan tool indicates that this test ran and passed, go to next step. If scan tool does not indicate that this test ran and passed, go to step 2 .
Using scan tool, select CAPTURE INFO, REVIEW INFO function.. If any undiagnosed DTCs are displayed, go to applicable DTC test. If no undiagnosed DTCs are displayed, system is okay.

If problem is intermittent, see appropriate TROUBLE SHOOTING - NO CODES article for diagnosis.

DTC P0200: INJECTOR CONTROL CIRCUIT (2.2L "J" BODY, 2.2L "S" SERIES & 2.4L "J" & "N" BODIES)

Note. For circuit reference, see appropriate wiring diagram in WIRING DIAGRAMS article.

Powertrain Control Module (PCM) has 4 injector driver circuits, one for each injector. PCM monitors current in each driver circuit by measuring a voltage drop through a fixed resistor and is able to control it. Current through each driver is allowed to rise to a peak or 4 amps to quickly open injectors. Current is then reduced to one amp to keep injector open. If current cannot reach 4 amps or injector driver is shorted to voltage, DTC P0200 will set.

For duplication of DTC, ensure engine is running and battery voltage is greater than 9 volts.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-introduction__on-board-diagnostic-obd-system-check) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Attempt to start engine. If engine starts, go to next step. If engine will not start, see NO START DIAGNOSIS in appropriate BASIC DIAGNOSTIC PROCEDURES article.
Turn ignition off. Remove air cleaner outlet resonator. Disconnect all injector connectors. Install an injector test light on No. 1 injector harness connector. Crank engine and observe test light. Check remaining fuel injectors. If test light flashes for all injectors, perform injector coil test. See FUEL SYSTEM in appropriate SYSTEM & COMPONENT TESTING article. If test light does not flash at all injectors, go to next step.
If test light did not flash in step 3) but was on steady, go to next step. If test light did not flash in step 3) and was off, go to step 8 .
Remove injector test light from affected circuit. Turn ignition off. Disconnect PCM harness connector containing affected fuel injector circuit. Using a test light connected to battery positive, probe affected fuel injector driver circuits. If test light illuminates, go to next step. If test light does not illuminate, go to step 7 .
Repair short to ground in fuel injector driver circuit. After repairs, go to step 14 .
Replace PCM. Program replacement PCM using required equipment. After repairs, go to step 14 .
Using a test light connected to ground, probe ignition feed circuit terminal at affected fuel injector harness connector. Crank engine. If test light illuminates, go to next step. If test light does not illuminate, go to step 10 .
With test light still connected to ground, probe fuel injector driver circuit terminal at affected injector harness connector. Crank engine. If test light does not illuminate, go to step 11 . If test light illuminates, go to step 12 .
Repair open in ignition feed circuit. After repairs, go to step 14 .
Check for open or faulty connection in fuel injector driver circuit. If a problem is found, go to step 13 . If circuit is okay, go to step 7 .
Repair short to voltage in fuel injector driver circuit. After repairs, go to step 14 .
Repair open or faulty connection in fuel injector driver circuit. After repairs, go to next step.
Reconnect all harness connectors. Using scan tool, clear DTCs. Start engine and allow it to idle. Ensure engine is at normal operating temperature. Operate vehicle within conditions required for setting this DTC. Select SPECIFIC DTC function, and then enter DTC which was set. If scan tool indicates that this test ran and passed, go to next step. If scan tool does not indicate that this test ran and passed, go to step 2 .
If any other DTCs are set, diagnose DTCs as necessary. If no other DTCs are set, system is okay.

An injector that is shorted to voltage or is disconnected while engine is operating will cause a DTC P0200 to set. A misfire related DTC should also be set indicating which cylinder is inoperative.

DTC P0201, P0202, P0203 &/OR P0204: INJECTOR CONTROL CIRCUIT FAULT (1.9L SATURN)

Note. For circuit reference, see appropriate wiring diagram in WIRING DIAGRAMS article.

The injector system on both the DOHC and SOHC engines utilize Sequential Fuel Injection (SFI). The PCM independently controls each fuel injector through a driver circuit, in accordance with intake valve opening. The driver circuit is internally located in the PCM, providing the ground for each injector. The length and time an injector is held open (grounded by PCM) is calculated based on engine speed, load and valve location from the crankshaft position sensor.

Any of these DTCs will set if an injector circuit is open, shorted to voltage or shorted to ground. The injector circuit is continuously checked when engine is running.

Attempt to start engine. If engine starts, go to next step. If engine does not start, check if DTCs are present. If all 4 injector DTCs are present, repair ignition voltage to injectors. Check injector fuse. If injector DTCs are not present, see NO START DIAGNOSIS in appropriate BASIC DIAGNOSTIC PROCEDURES article.
With engine running, check if any active injector faults are present. If injector faults are present, go to next step. If injector faults are not present, problem is intermittent. See «DIAGNOSTIC AIDS»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p0135-p0204) .
If injector fault is indicated as open/grounded, go to step 5 . If injector fault is indicated as shorted, go to next step. If injector fault is indicated as intermittent, check for proper harness routing and terminals for proper tightness.
Turn engine off. Disconnect harness connector to affected injector. Install injector test light. Start engine. If shorted condition still exists, check circuit to PCM for short to voltage or faulty PCM. If shorted condition does not exist, replace faulty injector.
Turn engine off. Disconnect harness connector to affected injector. Install injector test light. Turn ignition on. If test light illuminates, check injector driver circuit for short to ground or faulty PCM. If test light does not illuminate, go to next step.
Using scan tool, select injector test and pulse affected injector while observing injector light. If test light flashes, replace faulty injector. If test light does not flash, go to next step.
Using a test light connected to ground, probe affected injector's positive side terminal (ignition on). If test light illuminates, check for open in circuit to PCM, terminal tightness or faulty PCM. If test light does not illuminate, repair open in injector positive circuit.

When diagnosing an intermittent problem, use scan tool to review malfunction history diagnostic information. This data can be used to duplicate a problem. Check tightness to harness connector terminals. An open or shorted injector circuit will cause a misfire DTC. Diagnose an injector DTC first if an injector and misfire DTC is present. Fuel in the oil is a good suspect of a leaking or grounded injector. Battery voltage is supplied to each injector when ignition is on. Injector resistance should be 12 ohms.

DTC P0201: INJECTOR NO. 1 CONTROL CIRCUIT (3.0L "V" BODY)

Note. For circuit reference, see appropriate wiring diagram in WIRING DIAGRAMS article.

ECM will enable an injector on intake stroke of each cylinder. Ignition voltage is supplied directly to fuel injectors. ECM controls each injector by grounding control circuit via an internal driver.

Primary function of driver is to supply ground for component being controlled. Each driver has a fault line which is monitored by ECM. When ECM is commanding a component on, voltage of control circuit should be low (near zero). When ECM is commanding control circuit to component off, voltage potential of circuit should be high (near battery voltage). If fault detection circuit senses a voltage other than what is expected, DTC P0201 will set.

ECM will monitor injector circuit for short to ground, short to voltage, open circuit or an internally shorted or excessively low resistance at injector. If ECM detects any of these malfunctions, this DTC will set and affected driver will be disabled. ECM will continue to test circuit and if fault disappears, driver will be reactivated.

For duplication of DTC, ensure battery voltage is 7.5-15 volts, and engine speed is greater than 40 RPM.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-introduction__on-board-diagnostic-obd-system-check) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Start and idle engine. Using scan tool, monitor misfire current cylinder No. 1. If counter is incrementing, go to next step. If counter is not incrementing, see «DIAGNOSTIC AIDS»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p0135-p0204) .
Turn ignition off. Disconnect main fuel injector connector. Turn ignition on, with engine off. Using test light connected to battery positive, probe injector No. 1 harness connector control circuit (ECM side). If test light illuminates, go to next step. If test light does not illuminate, go to step 6 .
Turn ignition off. Disconnect ECM harness connector located in engine compartment relay center. If test light illuminates, go to step 11 . If test light does not illuminate, go to next step.
Turn ignition on, with engine off. Using test light connected to ground, probe injector No. 1 harness connector control circuit (ECM side). If test light illuminates, go to step 12 . If test light does not illuminate, go to step 15 .
Crank engine. If test light flashes about once per second, go to step 8 . If test light does not flash about once per second, go to next step.
Turn ignition off. Disconnect ECM harness connector located in engine compartment relay center. Using DVOM, check harness continuity of injector No. 1 control circuit between main injector and ECM harness connectors. If continuity is present, go to step 14 . If continuity is not present, go to step 10 .
Turn ignition off. Using a jumper wire, reconnect switched battery feed circuit in male half of main injector harness connector to switched battery feed circuit in female half of main injector harness connector. Using test light connected to ground, probe injector No. 1 harness connector control circuit (injector side). Turn ignition on, with engine off. If test light illuminates, go to step 13 . If test light does not illuminate, go to next step.
Check for poor connections and terminal tension at fuel injector harness connector or at main injector harness connector. Check injector control circuit for open, short to ground, or short to voltage between injector and main injector connector. Check for open in switched battery feed circuit between injector and wiring splice. Repair as necessary. After repairs, go to step 16 . If connections, terminals and circuits are okay, go to step 13 .
Repair open or high resistance in injector control circuit. After repairs, go to step 16 .
Repair short to ground in injector control circuit. After repairs, go to step 16 .
Repair short to voltage in injector driver circuit. After repairs, go to step 16 .
Replace fuel injector. After repairs, go to step 16 .
Check for poor connections and terminal tension at ECM harness connector. Repair as necessary. After repairs, go to step 16 . If connections and terminals are okay, go to next step.
Replace ECM. New ECM must be programmed with theft deterrent module frequency code currently on vehicle. After repairs, go to next step.
Using scan tool, clear DTCs. Turn ignition off for 15 seconds. Start engine and operate vehicle. Check for DTCs. If DTC P0201 is set, go to step 2 . If DTC P0201 is not set, go to next step.
If other DTCs were present during OBD system check and have not been diagnosed, go to applicable DTC. If no other DTCs are present, system is okay.

Check for poor connections at ECM or at component. Inspect harness connectors for backed-out terminals, improper mating, broken locks, improperly formed or damaged terminals and poor terminal-to-wire connection.

Check for misrouted wiring harness. Inspect harness to ensure that it is not routed too close to high voltage wires (spark plug wires) or too close to high current devices (generator, motors, solenoids).

Check for damaged wiring harness. If harness appears to be okay, observe scan tool while moving related connectors and wiring harnesses. A change in scan tool display may help to locate fault.

DTC P0201: INJECTOR NO. 1 CONTROL CIRCUIT (3.1L "N" & "W" BODIES & 3.4L "N" BODY & "U" SERIES)

Note. For circuit reference, see appropriate wiring diagram in WIRING DIAGRAMS article.

PCM controls fuel injector control circuit using an ignition feed driver and ground circuit within the PCM. The driver has the ability to detect an electrical malfunction in ignition feed or ground circuit. If an electrical malfunction occurs in fuel injector circuit for affected cylinder, ignition feed driver signals PCM to set DTC.

For duplication of DTC, engine must be running with an incorrect voltage level being detected on an injector driver circuit.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-introduction__on-board-diagnostic-obd-system-check) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Start and operate engine at idle. Using scan tool, monitor SPECIFIC DTC. If scan tool indicates that this DTC failed this ignition cycle, go to step 4 . If scan does not indicate that this DTC failed this ignition cycle, go to next step.
Turn ignition on, engine off. Using scan tool, review and record FAILURE RECORDS data. Operate vehicle in failure conditions parameter. If scan tool indicates that this DTC failed this ignition cycle, go to next step. If scan tool does not indicate that this DTC failed this ignition cycle, see «DIAGNOSTIC AIDS»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p0135-p0204) .
Using scan tool, enter OUTPUT DRIVER DATA menu. If scan tool indicates that cylinder No. 1 injector circuit is STUCK HIGH, go to step 6 . If scan tool does not indicate that cylinder No. 1 injector circuit is STUCK HIGH, go to next step.
If scan tool indicates that cylinder No. 1 injector circuit is STUCK LOW, go to step 10 . If scan tool does not indicate that cylinder No. 1 injector circuit is STUCK LOW, see «DIAGNOSTIC AIDS»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p0135-p0204) .
Turn ignition off. Disconnect 10-pin fuel injector harness connector. Crank engine. While cranking engine, if scan tool indicates that cylinder No. 1 injector circuit is STUCK LOW, go to next step. If scan tool does not indicate that cylinder No. 1 injector circuit is STUCK LOW, go to step 9 .
Turn ignition off. Disconnect PCM harness connector. Turn ignition on, engine off. Check voltage between cylinder No. 1 fuel injector control circuit and ground. If voltage is near battery voltage, go to next step. If voltage is not near battery voltage, go to step 15 .
Locate and repair short to voltage in cylinder No. 1 fuel injector control circuit. After repairs, go to step 16 .
If scan tool indicates that No. 1 injector control circuit is STUCK LOW, check affected fuel injector. Perform fuel injector coil test. See FUEL SYSTEM in appropriate SYSTEM & COMPONENT TESTING article.
Disconnect 10-pin fuel injector harness connector. Using a test light connected to battery positive, probe injector No. 1 control circuit at PCM side of 10-pin connector. If test light illuminates, go to next step. If test light does not illuminate, go to step 12 .
Disconnect PCM harness connector. Using a test light connected to battery positive, probe injector No. 1 control circuit at PCM connector. If test light illuminates, go to step 14 . If test light does not illuminate, go to step 15 .
With test light still connected, crank engine. If test light flashes, check affected fuel injector. Perform fuel injector coil test. See FUEL SYSTEM in appropriate SYSTEM & COMPONENT TESTING article. If test light does not flash, go to next step.
Check cylinder No. 1 injector driver circuit between 10-pin injector connector and PCM for an open circuit. Repair as necessary. After repairs, go to step 16 .
Locate and repair short to ground in fuel injector driver circuit between PCM and 10-pin injector connector. After repairs, go to step 16 .
Replace PCM. Program replacement PCM using required equipment. After repairs, go to next step.
Using scan tool, clear DTCs. Turn ignition off for 15 seconds. Start engine and operate vehicle within FAILURE RECORDS conditions. Check for DTCs. If this DTC is set, go to step 2 . If this DTC is not set, system is okay.

Monitor injector fault parameter on scan tool. Wiggle electrical harnesses for affected electrical circuit. If status changes on tool, an intermittent problem is present. Check for poor connections at PCM. Check for damaged harness.

DTC P0201: INJECTOR NO. 1 CONTROL CIRCUIT (3.5L "W" BODY)

Note. For circuit reference, see appropriate wiring diagram in WIRING DIAGRAMS article.

PCM will enable an injector on intake stroke of each cylinder. Ignition voltage is supplied directly to fuel injectors. PCM controls each injector by grounding control circuit via an internal driver.

Primary function of driver is to supply ground for component being controlled. Each driver has a fault line which is monitored by PCM. When PCM is commanding a component on, voltage of control circuit should be low (near zero volts). When PCM is commanding control circuit to component off, voltage potential of circuit should be high (near battery voltage). If fault detection circuit senses a voltage other than what is expected, DTC P0201 will set.

PCM will monitor injector circuit for short to ground, short to voltage, open circuit or an internally shorted or excessively low resistance at injector. If PCM detects any of these malfunctions, this DTC will set and affected driver will be disabled. PCM will continue to test circuit and if fault disappears, driver will be reactivated. For duplication of DTC, ensure engine is running, and ignition voltage is 9-17 volts.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-introduction__on-board-diagnostic-obd-system-check) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Start engine and let idle. Using scan tool, monitor injector circuit status for cylinder No. 1. If scan tool does not indicate a circuit fault, see «DIAGNOSTIC AIDS»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p0135-p0204) . If scan tool indicates a circuit fault, go to next step.
If an entire bank of cylinders is inoperative, go to next step. If an entire bank of cylinders is not inoperative, go to step 6 .
Inspect fuel injector fuses located in underhood fuse block assembly. If fuses are okay, go to next step. If either fuse is open, go to step 11 .
Turn ignition off. Disconnect No. 1 fuel injector harness connector. Turn ignition on. Measure voltage between ground and ignition feed circuit at No. 1 fuel injector harness connector. If battery voltage is present, go to next step. If battery voltage is not present, go to step 12 .
Connect injector test light to No. 1 injector harness connector. Crank engine. If test light flashes, go to step 18 . If test light does not flash, go to next step.
Turn ignition off. Disconnect PCM harness connector. Measure resistance in injector control circuit between injector No. 1 and PCM. If resistance is 5 ohms or less, go to next step. If resistance is not 5 ohms or less, go to step 13 .
Check for continuity between injector control circuit and ground. If continuity is present, go to step 14 . If continuity is not present, go to next step.
Turn ignition on, with engine off. Check for voltage on injector control circuit. If any voltage is present, go to step 15 . If no voltage is present, go to next step.
Turn ignition off. Disconnect all fuel injectors. Check for continuity between fuel injector control circuits. If continuity is present between any circuits, go to step 16 . If continuity is not present between any circuit, go to step 20 .
Check for short to ground in injector ignition feed circuit. Repair as necessary. After repairs, go to step 22 . If circuit is okay, go to step 17 .
Repair open or high resistance in injector ignition feed circuit. After repairs, go to step 22 .
Repair open or high resistance in injector control circuit. After repairs, go to step 22 .
Repair short to ground in injector control circuit. After repairs, go to step 22 .
Repair short to voltage in injector control circuit. After repairs, go to step 22 .
Repair injector control circuits that are shorted together. After repairs, go to step 22 .
Check fuel injector. Perform fuel injector coil test. See FUEL SYSTEM in appropriate SYSTEM & COMPONENT TESTING article. Repair as necessary. After repairs, go to step 22 .
Check for poor connections and improper terminal tension at fuel injector. Repair as necessary. After repairs, go to step 22 . If connections and terminal tension is okay, go to next step.
Replace fuel injector. After repairs, go to step 22 .
Check for poor connections and improper terminal tension at PCM. Repair as necessary. After repairs, go to step 22 . If connections and terminal tension is okay, go to next step.
Replace PCM. Program replacement PCM using required equipment. After repairs, go to next step.
Using scan tool, clear DTCs. Turn ignition off for 15 seconds. Start engine and operate vehicle. Check for DTCs. If DTC P0201 is set, go to step 2 . If DTC P0201 is not set, go to next step.
If other DTCs were present during OBD system check and have not been diagnosed, go to applicable DTC. If no other DTCs are present, system is okay.

For any test that requires probing PCM or component harness connectors, use Connector Test Adapter Kit (J-35616-A). This will prevent damage to harness connector terminals. Check for the following conditions

Check for poor connections at PCM or at component. Inspect harness connectors for backed-out terminals, improper mating, broken locks, improperly formed or damaged terminals and poor terminal-to-wire connection.

Check for damaged wiring harness. If harness appears to be okay, observe scan tool while moving related connectors and wiring harnesses. A change in scan tool display may help to locate fault.

DTC P0201: INJECTOR NO. 1 CONTROL CIRCUIT (3.8L "C", "F", "G", "H" & "W" BODIES)

Note. For circuit reference, see appropriate wiring diagram in WIRING DIAGRAMS article.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-introduction__on-board-diagnostic-obd-system-check) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Start and operate engine at idle. Using scan tool, monitor SPECIFIC DTC. If scan tool indicates that this DTC failed this ignition cycle, go to step 4 . If scan does not indicate that this DTC failed this ignition cycle, go to next step.
Turn ignition on, engine off. Using scan tool, review and record FAILURE RECORDS data. Operate vehicle in fail conditions parameter. If scan tool indicates that this DTC failed this ignition cycle, go to next step. If scan tool does not indicate that this DTC failed this ignition cycle, see «DIAGNOSTIC AIDS»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p0135-p0204) .
Turn ignition off. Disconnect PCM harness connector. Turn ignition on, engine off. Check voltage between cylinder No. 1 fuel injector control circuit and ground. If voltage is near battery voltage, go to next step. If voltage is not near battery voltage, go to step 9 .
Check fuel injectors. Perform fuel injector coil test. See FUEL SYSTEM in appropriate SYSTEM & COMPONENT TESTING article. If injectors are okay, go to next step. If injectors are not okay, go to step 17 .
Turn ignition off. Disconnect cylinder No. 1 injector connector. Turn ignition on. Check voltage between ground and fuel injector No. 1 control circuit at PCM connector. If voltage is zero volts, go to next step. If voltage is not zero volts, go to step 16 .
Check for intermittent open in ignition feed circuit in harness between fuse and injector No. 1. Check for intermittent open in injector No. 1 control circuit between PCM and injector. Repair as necessary. After repairs, go to step 19 . If circuits are okay, go to next step.
Check for poor terminal connections at fuel injector No. 1 connector and injector No. 1 connection at PCM connector. Repair as necessary. After repairs, go to step 19 . If connections are okay, go to step 18 .
Turn ignition off. Disconnect injector No. 1 connector. Turn ignition on. Check voltage between ground and ignition feed circuit at injector No. 1 connector. If battery voltage is present, go to next step. If battery voltage is not present, go to step 14 .
Using a test light connected to battery positive, probe injector No. 1 control circuit. If test light illuminates, go to step 15 . If test light does not illuminate, go to step 11 .
Turn ignition off. Using a fused jumper wire, jumper injector No. 1 control circuit and ignition feed circuit at injector connector. Turn ignition on. Using test light connected to ground, probe injector No. 1 control circuit at PCM connector. If test light illuminates, go to next step. If test light does not illuminate, go to step 13 .
Check for poor terminal contact at injector No. 1 connector. Repair as necessary. After repairs, go to step 19 . If connection is okay, go to step 17 .
Locate and repair open in injector No. 1 control circuit. After repairs, go to step 19 .
Locate and repair open or short to ground in injector No. 1 ignition feed circuit. After repairs, go to step 19 .
Locate and repair short to ground in injector No. 1 control circuit. After repairs, go to step 19 .
Locate and repair short to voltage in injector No. 1 control circuit. After repairs, go to step 19 .
Replace faulty injector. After repairs, go to step 19 .
Replace PCM. Program replacement PCM using required equipment. After repairs, go to next step.
Using scan tool, clear DTCs. Turn ignition off for 15 seconds. Start engine and operate vehicle within FAILURE RECORDS conditions. Check for DTCs. If this DTC is set, go to step 2 . If this DTC is not set, system is okay.

DTC P0201: INJECTOR NO. 1 CONTROL CIRCUIT (4.0L "G" BODY & 4.6L "E" & "K" BODIES)

Note. For circuit reference, see appropriate wiring diagram in WIRING DIAGRAMS article.

The PCM contains a General Field Effect Transistor Driver (GFD) that controls the 8 fuel injector drivers. The GFD is used to determine if there is a problem with any of the fuel injector circuits. The GFD has a fault line for each injector. The fault line goes high when an open, short to ground, or short to voltage is noticed in an injector circuit. DTC P0201 will set when the fault line for an injector is high.

For duplication of DTC, ensure DTCs P0560 and P1376 are not set and ignition voltage is 10-16 volts.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-introduction__on-board-diagnostic-obd-system-check) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Turn ignition on. Using scan tool, check if DTCs P0204, P0206 and P0207 are also present. If these DTCs are present, go to next step. If these DTCs are not present, go to step 7 .
Turn ignition off. Remove and inspect INJ 2 fuse (10-amp). If fuse is open, go to next step. If fuse is okay, go to step 6 .
Disconnect fuel rail harness connector. Using DVOM, measure resistance between fuel rail harness connector terminal "N" and ground. If resistance is greater than 5 ohms, go to next step. If resistance is not greater than 5 ohms, go to step 17 .
Disconnect injector No. 1 harness connector. Measure resistance between injector No. 1 harness connector terminal "A" and ground. Repeat test for injectors No. 4, 6 and 7. If resistance is less than 5 ohms on any of the circuits, go to step 18 . If resistance is not less than 5 ohms on any of the circuits, go to step 19 .
Disconnect fuel rail harness connector. Replace INJ 2 fuse. Turn ignition on. Using DVOM, measure voltage between fuel rail harness connector terminal "N" and ground. If voltage is 10 volts or greater, go to step 20 . If voltage is not 10 volts or greater, go to step 21 .
Using scan tool, select DTC INFO and LAST TST. FAIL mode. If this DTC failed its last test, go to step 9 . If this DTC does not show that it failed its last test, go to next step.
Clear DTCs and operate vehicle until DTC P0201 resets. If DTC P0201 resets, go to next step. If DTC P0201 does not reset, fault is not present.
Turn ignition off. Disconnect injector No. 1 harness connector. Turn ignition on. Measure voltage between injector No. 1 harness connector terminal "A" and ground. If voltage is 10 volts or greater, go to next step. If voltage is not 10 volts or greater, go to step 22 .
Reconnect injector No. 1 harness connector. Store fluid life reading as indicated on scan tool. Turn ignition off for 30 seconds, and then disconnect PCM harness connector C2. Turn ignition on. Measure voltage between PCM harness connector C2 terminal No. 9 and ground. If voltage is less than 10 volts, go to next step. If voltage is not less than 10 volts, go to step 14 .
Disconnect injector No. 1 harness connector. Measure resistance between injector terminals "A" and "B". If resistance is greater than 8 ohms, go to next step. If resistance is not greater than 8 ohms, go to step 27 .
Measure voltage between injector No. 1 harness connector terminal "B". If voltage is 0.1 volt or less, go to next step. If voltage is not 0.1 volt or less, go to step 23 .
Check terminal contact at PCM harness connector C2. Repair as necessary. If terminal contact is okay, go to step 28 .
Turn ignition off. Reconnect PCM harness connector C2. Disconnect fuel rail harness connector. Turn ignition on. Measure voltage between injector harness terminal "A" and ground. If voltage is less than 10 volts, go to next step. If voltage is not less than 10 volts, go to step 24 .
Disconnect injector No. 1 harness connector. Measure resistance between injector terminal "A" and ground. If resistance is greater than 10,000 ohms, go to next step. If resistance is not greater than 10,000 ohms, go to step 25 .
Measure resistance between injector terminals "A" and "B". If resistance is greater than 25 ohms, go to step 27 . If resistance is not greater than 25 ohms, go to step 26 .
Repair short to ground between fuse and fuel rail connector.
Repair short to ground between fuel rail connector and injector connector that low resistance was measured on.
Replace INJ 2 fuse and retest for DTCs.
Repair open in circuit between splice and fuel rail connector.
Repair open in circuit between INJ 2 fuse and fuel rail connector, or repair poor terminal contact at fuse.
Repair open in circuit between splice and injector No. 1.
Repair short to voltage in injector No. 1 control circuit.
Repair open or short to ground in injector No. 1 control circuit.
Repair short to ground in injector No. 1 control circuit.
Repair open in injector No. 1 control circuit.
Replace fuel injector.
Replace PCM. Program replacement PCM using required equipment.

DTC P0202: INJECTOR NO. 2 CONTROL CIRCUIT (3.0L "V" BODY)

Note. For circuit reference, see appropriate wiring diagram in WIRING DIAGRAMS article.

ECM will enable an injector on intake stroke of each cylinder. Ignition voltage is supplied directly to fuel injectors. ECM controls each injector by grounding control circuit via an internal driver.

Primary function of driver is to supply ground for component being controlled. Each driver has a fault line which is monitored by ECM. When ECM is commanding a component on, voltage of control circuit should be low (near zero volts). When ECM is commanding control circuit to component off, voltage potential of circuit should be high (near battery voltage). If fault detection circuit senses a voltage other than what is expected, DTC P0202 will set.

For duplication of DTC, ensure ignition voltage is 7.5-15 volts, and engine speed is greater than 80 RPM.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-introduction__on-board-diagnostic-obd-system-check) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Start and idle engine. Using scan tool, monitor misfire current cylinder No. 2. If counter is incrementing, go to next step. If counter is not incrementing, see «DIAGNOSTIC AIDS»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p0135-p0204) .
Turn ignition off. Disconnect main fuel injector connector. Turn ignition on, with engine off. Using test light connected to battery positive, probe injector No. 2 harness connector control circuit (ECM side). If test light illuminates, go to next step. If test light does not illuminate, go to step 6 .
Turn ignition off. Disconnect ECM harness connector located in engine compartment relay center. If test light illuminates, go to step 11 . If test light does not illuminate, go to next step.
Turn ignition on, with engine off. Using test light connected to ground, probe injector No. 2 harness connector control circuit (ECM side). If test light illuminates, go to step 12 . If test light does not illuminate, go to step 15 .
Crank engine. If test light flashes about once per second, go to step 8 . If test light does not flash about once per second, go to next step.
Turn ignition off. Disconnect ECM harness connector located in engine compartment relay center. Using DVOM, check harness continuity of injector No. 2 control circuit between main injector and ECM harness connectors. If continuity is present, go to step 14 . If continuity is not present, go to step 10 .
Turn ignition off. Using a jumper wire, reconnect switched battery feed circuit in male half of main injector harness connector to switched battery feed circuit in female half of main injector harness connector. Using test light connected to ground, probe injector No. 2 harness connector control circuit (injector side). Turn ignition on, with engine off. If test light illuminates, go to step 13 . If test light does not illuminate, go to next step.
Check for poor connections and terminal tension at fuel injector harness connector or at main injector harness connector. Check injector control circuit for open, short to ground, or short to voltage between injector and main injector connector. Check for open in switched battery feed circuit between injector and wiring splice. Repair as necessary. After repairs, go to step 16 . If connections, terminals and circuits are okay, go to step 13 .
Repair open or high resistance in injector control circuit. After repairs, go to step 16 .
Repair short to ground in injector control circuit. After repairs, go to step 16 .
Repair short to voltage in injector driver circuit. After repairs, go to step 16 .
Replace fuel injector. After repairs, go to step 16 .
Check for poor connections and terminal tension at ECM harness connector. Repair as necessary. After repairs, go to step 16 . If connections and terminals are okay, go to next step.
Replace ECM. New ECM must be programmed with theft deterrent module frequency code currently on vehicle. After repairs, go to next step.
Using scan tool, clear DTCs. Turn ignition off for 15 seconds. Start engine and operate vehicle. Check for DTCs. If DTC P0202 is set, go to step 2 . If DTC P0202 is not set, go to next step.
If other DTCs were present during OBD system check and have not been diagnosed, go to applicable DTC. If no other DTCs are present, system is okay.

Check for damaged wiring harness. If harness appears to be okay, observe scan tool while moving related connectors and wiring harnesses. A change in scan tool display may help to locate fault.

DTC P0202: INJECTOR NO. 2 CONTROL CIRCUIT (3.1L "N" & "W" BODIES & 3.4L "N" BODY & "U" SERIES)

Note. For circuit reference, see appropriate wiring diagram in WIRING DIAGRAMS article.

For duplication of DTC, engine must be running with an incorrect voltage level being detected on an injector driver circuit.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-introduction__on-board-diagnostic-obd-system-check) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Start and operate engine at idle. Using scan tool, monitor SPECIFIC DTC. If scan tool indicates that this DTC failed this ignition cycle, go to step 4 . If scan does not indicate that this DTC failed this ignition cycle, go to next step.
Turn ignition on, engine off. Using scan tool, review and record FAILURE RECORDS data. Operate vehicle in failure conditions parameter. If scan tool indicates that this DTC failed this ignition cycle, go to next step. If scan tool does not indicate that this DTC failed this ignition cycle, see «DIAGNOSTIC AIDS»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p0135-p0204) .
Using scan tool, enter OUTPUT DRIVER DATA menu. If scan tool indicates that cylinder No. 2 injector circuit is STUCK HIGH, go to step 6 . If scan tool does not indicate that cylinder No. 2 injector circuit is STUCK HIGH, go to next step.
If scan tool indicates that cylinder No. 2 injector circuit is STUCK LOW, go to step 10 . If scan tool does not indicate that cylinder No. 2 injector circuit is STUCK LOW, see «DIAGNOSTIC AIDS»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p0135-p0204) .
Turn ignition off. Disconnect 10-pin fuel injector harness connector. Crank engine. While cranking engine, if scan tool indicates that cylinder No. 2 injector circuit is STUCK LOW, go to next step. If scan tool does not indicate that cylinder No. 2 injector circuit is STUCK LOW, go to step 9 .
Turn ignition off. Disconnect PCM harness connector. Turn ignition on, with engine off. Measure voltage between cylinder No. 2 fuel injector control circuit and ground. If voltage is near battery voltage, go to next step. If voltage is not near battery voltage, go to step 15 .
Locate and repair short to voltage in cylinder No. 2 fuel injector control circuit. After repairs, go to step 16 .
If scan tool indicates that No. 2 injector control circuit is STUCK LOW, check affected fuel injector. Perform fuel injector coil test. See FUEL SYSTEM in appropriate SYSTEM & COMPONENT TESTING article.
Disconnect 10-pin fuel injector harness connector. Using a test light connected to battery positive, probe injector No. 2 control circuit at PCM side of 10-pin connector. If test light illuminates, go to next step. If test light does not illuminate, go to step 12 .
Disconnect PCM harness connector. Using a test light connected to battery positive, probe injector No. 2 control circuit at PCM connector. If test light illuminates, go to step 14 . If test light does not illuminate, go to step 15 .
With test light still connected, crank engine. If test light flashes, check affected fuel injector. Perform fuel injector coil test. See FUEL SYSTEM in appropriate SYSTEM & COMPONENT TESTING article. If test light does not flash, go to next step.
Check cylinder No. 2 injector driver circuit between 10-pin injector connector and PCM for an open circuit. Repair as necessary. After repairs, go to step 16 .
Locate and repair short to ground in fuel injector driver circuit between PCM and 10-pin injector connector. After repairs, go to step 16 .
Replace PCM. Program replacement PCM using required equipment. After repairs, go to next step.
Using scan tool, clear DTCs. Turn ignition off for 15 seconds. Start engine and operate vehicle with the FAILURE RECORDS conditions. Check for DTCs. If this DTC is set, go to step 2 . If this DTC is not set, system is okay.

DTC P0202: INJECTOR NO. 2 CONTROL CIRCUIT (3.5L "W" BODY)

Note. For circuit reference, see appropriate wiring diagram in WIRING DIAGRAMS article.

PCM will enable an injector on intake stroke of each cylinder. Ignition voltage is supplied directly to fuel injectors. PCM controls each injector by grounding control circuit via an internal driver.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-introduction__on-board-diagnostic-obd-system-check) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Start engine and let idle. Using scan tool, monitor injector circuit status for cylinder No. 2. If scan tool does not indicate a circuit fault, see «DIAGNOSTIC AIDS»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p0135-p0204) . If scan tool does indicates a circuit fault, go to next step.
If an entire bank of cylinders is inoperative, go to next step. If an entire bank of cylinders is not inoperative, go to step 6 .
Inspect fuel injector fuses located in underhood fuse block assembly. If fuses are okay, go to next step. If either fuse is open, go to step 11 .
Turn ignition off. Disconnect No. 2 fuel injector harness connector. Turn ignition on. Measure voltage between ground and ignition feed circuit at No. 2 fuel injector harness connector. If battery voltage is present, go to next step. If battery voltage is not present, go to step 12 .
Connect injector test light to No. 2 injector harness connector. Crank engine. If test light flashes, go to step 18 . If test light does not flash, go to next step.
Turn ignition off. Disconnect PCM harness connector. Measure resistance in injector control circuit between injector No. 2 and PCM. If resistance is 5 ohms or less, go to next step. If resistance is not 5 ohms or less, go to step 13 .
Check for continuity between injector control circuit and ground. If continuity is present, go to step 14 . If continuity is not present, go to next step.
Turn ignition on, with engine off. Check for voltage on injector control circuit. If any voltage is present, go to step 15 . If no voltage is present, go to next step.
Turn ignition off. Disconnect all fuel injectors. Check for continuity between fuel injector control circuits. If continuity is present between any circuits, go to step 16 . If continuity is not present between any circuit, go to step 20 .
Check for short to ground in injector ignition feed circuit. Repair as necessary. After repairs, go to step 22 . If circuit is okay, go to step 17 .
Repair open or high resistance in injector ignition feed circuit. After repairs, go to step 22 .
Repair open or high resistance in injector control circuit. After repairs, go to step 22 .
Repair short to ground in injector control circuit. After repairs, go to step 22 .
Repair short to voltage in injector control circuit. After repairs, go to step 22 .
Repair injector control circuits that are shorted together. After repairs, go to step 22 .
Check fuel injector. Perform fuel injector coil test. See FUEL SYSTEM in appropriate SYSTEM & COMPONENT TESTING article. Repair as necessary. After repairs, go to step 22 .
Check for poor connections and improper terminal tension at fuel injector. Repair as necessary. After repairs, go to step 22 . If connections and terminal tension is okay, go to next step.
Replace fuel injector. After repairs, go to step 22 .
Check for poor connections and improper terminal tension at PCM. Repair as necessary. After repairs, go to step 22 . If connections and terminal tension is okay, go to next step.
Replace PCM. Program replacement PCM using required equipment. After repairs, go to next step.
Using scan tool, clear DTCs. Turn ignition off for 15 seconds. Start engine and operate vehicle. Check for DTCs. If DTC P0201 is set, go to step 2 . If DTC P0201 is not set, go to next step.
If other DTCs were present during OBD system check and have not been diagnosed, go to applicable DTC. If no other DTCs are present, system is okay.

Check for damaged wiring harness. If harness appears to be okay, observe scan tool while moving related connectors and wiring harnesses. A change in scan tool display may help to locate fault.

DTC P0202: INJECTOR NO. 2 CONTROL CIRCUIT (3.8L "C", "F", "G", "H" & "W" BODIES)

Note. For circuit reference, see appropriate wiring diagram in WIRING DIAGRAMS article.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-introduction__on-board-diagnostic-obd-system-check) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Start and operate engine at idle. Using scan tool, monitor SPECIFIC DTC. If scan tool indicates that this DTC failed this ignition cycle, go to step 4 . If scan does not indicate that this DTC failed this ignition cycle, go to next step.
Turn ignition on, engine off. Using scan tool, review and record FAILURE RECORDS data. Operate vehicle in failure conditions parameter. If scan tool indicates that this DTC failed this ignition cycle, go to next step. If scan tool does not indicate that this DTC failed this ignition cycle, see «DIAGNOSTIC AIDS»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p0135-p0204) .
Turn ignition off. Disconnect PCM harness connector. Turn ignition on, engine off. Measure voltage between cylinder No. 2 fuel injector control circuit and ground. If voltage is near battery voltage, go to next step. If voltage is not near battery voltage, go to step 9 .
Check fuel injectors. Perform fuel injector coil test. See FUEL SYSTEM in appropriate SYSTEM & COMPONENT TESTING article. If injectors are okay, go to next step. If injectors are not okay, go to step 17 .
Turn ignition off. Disconnect cylinder No. 2 injector connector. Turn ignition on. Measure voltage between ground and fuel injector No. 2 control circuit at PCM connector. If voltage is near zero volts, go to next step. If voltage is not near zero volts, go to step 16 .
Check for intermittent open in ignition feed circuit in harness between fuse and injector No. 2. Check for intermittent open in injector No. 2 control circuit between PCM and injector. Repair as necessary. After repairs, go to step 19 . If circuits are okay, go to next step.
Check for poor terminal connections at fuel injector No. 2 connector and injector No. 2 connection at PCM connector. Repair as necessary. After repairs, go to step 19 . If connections are okay, go to step 18 .
Turn ignition off. Disconnect injector No. 2. Turn ignition on. Measure voltage between ground and ignition feed circuit at injector No. 2 connector. If battery voltage is present, go to next step. If battery voltage is not present, go to step 14 .
Using a test light connected to battery positive, probe injector No. 2 control circuit. If test light illuminates, go to step 15 . If test light does not illuminate, go to next step.
Turn ignition off. Using a fused jumper wire, jumper injector No. 2 control circuit and ignition feed circuit at injector connector. Turn ignition on. Using test light connected to ground, probe injector No. 2 control circuit at PCM connector. If test light illuminates, go to next step. If test light does not illuminate, go to step 13 .
Check for poor terminal contact at injector No. 2 connector. Repair as necessary. After repairs, go to step 19 . If connection is okay, go to step 17 .
Locate and repair open in injector No. 2 control circuit. After repairs, go to step 19 .
Locate and repair open or short to ground in injector No. 2 ignition feed circuit. After repairs, go to step 19 .
Locate and repair short to ground in injector No. 2 control circuit. After repairs, go to step 19 .
Locate and repair short to voltage in injector No. 2 control circuit. After repairs, go to step 19 .
Replace faulty injector. After repairs, go to step 19 .
Replace PCM. Program replacement PCM using required equipment. After repairs, go to next step.
Using scan tool, clear DTCs. Turn ignition off for 15 seconds. Start engine and operate vehicle with the FAILURE RECORDS conditions. Check for DTCs. If this DTC is set, go to step 2 . If this DTC is not set, system is okay.

DTC P0202: INJECTOR NO. 2 CONTROL CIRCUIT (4.0L "G" BODY & 4.6L "E" & "K" BODIES)

Note. For circuit reference, see appropriate wiring diagram in WIRING DIAGRAMS article.

The PCM contains a General Field Effect Transistor Driver (GFD) that controls the 8 fuel injector drivers. The GFD is used to determine if there is a problem with any of the fuel injector circuits. The GFD has a fault line for each injector. The fault line goes high when an open, short to ground, or short to voltage is noticed in an injector circuit. DTC P0202 will set when the fault line for an injector is high.

For duplication of DTC, ensure DTCs P0560 and P1376 not set, and ignition voltage is 10-16 volts.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-introduction__on-board-diagnostic-obd-system-check) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Turn ignition on. Using scan tool, check if DTCs P0203, P0205 and P0208 are also present. If these DTCs are present, go to next step. If these DTCs are not present, go to step 7 .
Turn ignition off. Remove and inspect INJ 1 fuse (10-amp). If fuse is open, go to next step. If fuse is okay, go to step 6 .
Disconnect fuel rail harness connector. Using DVOM, measure resistance between fuel rail harness connector terminal "P" and ground. If resistance is greater than 5 ohms, go to next step. If resistance is not greater than 5 ohms, go to step 17 .
Disconnect injector No. 2 harness connector. Measure resistance between injector No. 2 harness connector terminal "A" and ground. Repeat test for injectors No. 3, 5 and 8. If resistance is less than 5 ohms on any of the circuits, go to step 18 . If resistance is not less than 5 ohms on any of the circuits, go to step 19 .
Disconnect fuel rail harness connector. Replace INJ 1 fuse. Turn ignition on. Using DVOM, measure voltage between fuel rail harness connector terminal "P" and ground. If voltage is 10 volts or greater, go to step 20 . If voltage is not 10 volts or greater, go to step 21 .
Using scan tool, select DTC INFO, and then LAST TST. FAIL mode. If this DTC failed its last test, go to step 9 . If this DTC does not show that it failed its last test, go to next step.
Clear DTCs and operate vehicle until DTC P0202 resets. If DTC P0202 resets, go to next step. If DTC P0202 does not reset, fault is not present.
Turn ignition off. Disconnect injector No. 2 harness connector. Turn ignition on. Measure voltage between injector No. 2 harness connector terminal "A" and ground. If voltage is 10 volts or greater, go to next step. If voltage is less than 10 volts, go to step 22 .
Reconnect injector No. 2 harness connector. Store fluid life reading as indicated on scan tool. Turn ignition off for 30 seconds, and then disconnect PCM harness connector C2. Turn ignition on. Measure voltage between PCM harness connector C2 terminal No. 10 and ground. If voltage is less than 10 volts, go to next step. If voltage is not less than 10 volts, go to step 14 .
Disconnect injector No. 2 harness connector. Measure resistance between injector terminals "A" and "B". If resistance is greater than 8 ohms, go to next step. If resistance is not greater than 8 ohms, go to step 27 .
Measure voltage between ground and injector No. 2 harness connector terminal "B". If voltage is 0.1 volt or less, go to next step. If voltage is not 0.1 volt or less, go to step 23 .
Check terminal contact at PCM harness connector C2. Repair as necessary. If terminal contact is okay, go to step 28 .
Turn ignition off. Reconnect PCM harness connector C2. Disconnect fuel rail harness connector. Turn ignition on. Measure voltage between injector harness terminal "B" and ground. If voltage is less than 10 volts, go to next step. If voltage is not less than 10 volts, go to step 24 .
Disconnect injector No. 2 harness connector. Measure resistance between injector terminal "B" and ground. If resistance is greater than 10,000 ohms, go to next step. If resistance is not greater than 10,000 ohms, go to step 25 .
Measure resistance between injector terminals "A" and "B". If resistance is greater than 25 ohms, go to step 27 . If resistance is not greater than 25 ohms, go to step 26 .
Repair short to ground in injector ignition feed circuit between fuse and fuel rail connector.
Repair short to ground in injector ignition feed circuit between fuel rail connector and injector connector that low resistance was measured on.
Replace INJ 1 fuse and retest for DTCs.
Repair open in injector ignition feed circuit between splice and fuel rail connector.
Repair open in injector ignition feed circuit between INJ 1 fuse and fuel rail connector, or repair poor terminal contact at fuse.
Repair open in injector ignition feed circuit between splice and injector No. 2.
Repair short to voltage in injector No. 2 control circuit.
Repair open or short to ground in injector No. 2 control circuit.
Repair short to ground in injector No. 2 control circuit.
Repair open in injector No. 2 control circuit.
Replace fuel injector.
Replace PCM. Program replacement PCM using required equipment.

DTC P0203: INJECTOR NO. 3 CONTROL CIRCUIT (3.0L "V" BODY)

Note. For circuit reference, see appropriate wiring diagram in WIRING DIAGRAMS article.

ECM will enable an injector on intake stroke of each cylinder. Ignition voltage is supplied directly to fuel injectors. ECM controls each injector by grounding control circuit via an internal driver.

Primary function of driver is to supply ground for component being controlled. Each driver has a fault line which is monitored by ECM. When ECM is commanding a component on, voltage of control circuit should be low (near zero volts). When ECM is commanding control circuit to component off, voltage potential of circuit should be high (near battery voltage). If fault detection circuit senses a voltage other than what is expected, DTC P0203 will set.

For duplication of DTC, ensure ignition voltage is 7.5-15 volts, and engine speed is greater than 80 RPM.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-introduction__on-board-diagnostic-obd-system-check) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Start and idle engine. Using scan tool, monitor misfire current cylinder No. 3. If counter is incrementing, go to next step. If counter is not incrementing, see «DIAGNOSTIC AIDS»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p0135-p0204) .
Turn ignition off. Disconnect main fuel injector connector. Turn ignition on, with engine off. Using test light connected to battery positive, probe injector No. 3 harness connector control circuit (ECM side). If test light illuminates, go to next step. If test light does not illuminate, go to step 6 .
Turn ignition off. Disconnect ECM harness connector located in engine compartment relay center. If test light illuminates, go to step 11 . If test light does not illuminate, go to next step.
Turn ignition on, with engine off. Using test light connected to ground, probe injector No. 3 harness connector control circuit (ECM side). If test light illuminates, go to step 12 . If test light does not illuminate, go to step 15 .
Crank engine. If test light flashes about once per second, go to step 8 . If test light does not flash about once per second, go to next step.
Turn ignition off. Disconnect ECM harness connector located in engine compartment relay center. Using DVOM, check harness continuity of injector No. 3 control circuit between main injector and ECM harness connectors. If continuity is present, go to step 14 . If continuity is not present, go to step 10 .
Turn ignition off. Using a jumper wire, reconnect switched battery feed circuit in male half of main injector harness connector to switched battery feed circuit in female half of main injector harness connector. Using test light connected to ground, probe injector No. 3 harness connector control circuit (injector side). Turn ignition on, with engine off. If test light illuminates, go to step 13 . If test light does not illuminate, go to next step.
Check for poor connections and terminal tension at fuel injector harness connector or at main injector harness connector. Check injector control circuit for open, short to ground, or short to voltage between injector and main injector connector. Check for open in switched battery feed circuit between injector and wiring splice. Repair as necessary. After repairs, go to step 16 . If connections, terminals and circuits are okay, go to step 13 .
Repair open or high resistance in injector control circuit. After repairs, go to step 16 .
Repair short to ground in injector control circuit. After repairs, go to step 16 .
Repair short to voltage in injector driver circuit. After repairs, go to step 16 .
Replace fuel injector. After repairs, go to step 16 .
Check for poor connections and terminal tension at ECM harness connector. Repair as necessary. After repairs, go to step 16 . If connections and terminals are okay, go to next step.
Replace ECM. NEW ECM must be programmed with theft deterrent module frequency code currently on vehicle. After repairs, go to next step.
Using scan tool, clear DTCs. Turn ignition off for 15 seconds. Start engine and operate vehicle. Check for DTCs. If DTC P0203 is set, go to step 2 . If DTC P0203 is not set, go to next step.
If other DTCs were present during OBD system check and have not been diagnosed, go to applicable DTC. If no other DTCs are present, system is okay.

Check for damaged wiring harness. If harness appears to be okay, observe scan tool while moving related connectors and wiring harnesses. A change in scan tool display may help to locate fault.

DTC P0203: INJECTOR NO. 3 CONTROL CIRCUIT (3.1L "N" & "W" BODIES & 3.4L "N" BODY & "U" SERIES)

Note. For circuit reference, see appropriate wiring diagram in WIRING DIAGRAMS article.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-introduction__on-board-diagnostic-obd-system-check) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Start and operate engine at idle. Using scan tool, monitor SPECIFIC DTC. If scan tool indicates that this DTC failed this ignition cycle, go to step 4 . If scan does not indicate that this DTC failed this ignition cycle, go to next step.
Turn ignition on, engine off. Using scan tool, review and record FAILURE RECORDS data. Operate vehicle in failure conditions parameter. If scan tool indicates that this DTC failed this ignition cycle, go to next step. If scan tool does not indicate that this DTC failed this ignition cycle, see «DIAGNOSTIC AIDS»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p0135-p0204) .
Using scan tool, enter OUTPUT DRIVER DATA menu. If scan tool indicates that cylinder No. 3 injector circuit is STUCK HIGH, go to step 6 . If scan tool does not indicate that cylinder No. 3 injector circuit is STUCK HIGH, go to next step.
If scan tool indicates that cylinder No. 3 injector circuit is STUCK LOW, go to step 10 . If scan tool does not indicate that cylinder No. 3 injector circuit is STUCK LOW, see «DIAGNOSTIC AIDS»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p0135-p0204) .
Turn ignition off. Disconnect 10-pin fuel injector harness connector. Crank engine. While cranking engine, if scan tool indicates that cylinder No. 3 injector circuit is STUCK HIGH, go to next step. If scan tool does not indicate that cylinder No. 3 injector circuit is STUCK HIGH, go to step 9 .
Turn ignition off. Disconnect PCM harness connector. Turn ignition on, with engine off. Measure voltage between cylinder No. 3 fuel injector control circuit and ground. If voltage is near battery voltage, go to next step. If voltage is not near battery voltage, go to step 15 .
Locate and repair short to voltage in cylinder No. 3 fuel injector control circuit. After repairs, go to step 16 .
If scan tool indicates that No. 3 injector control circuit is STUCK LOW, check affected fuel injector. Perform fuel injector coil test. See FUEL SYSTEM in appropriate SYSTEM & COMPONENT TESTING article.
Disconnect 10-pin fuel injector harness connector. Using a test light connected to battery positive, probe injector No. 3 control circuit at PCM side of 10-pin connector. If test light illuminates, go to next step. If test light does not illuminate, go to step 12 .
Disconnect PCM harness connector. Using a test light connected to battery positive, probe injector No. 3 control circuit at PCM harness connector. If test light illuminates, go to step 14 . If test light does not illuminate, go to step 15 .
With test light still connected, crank engine. If test light flashes, check affected fuel injector. Perform fuel injector coil test. See FUEL SYSTEM in appropriate SYSTEM & COMPONENT TESTING article. If test light does not flash, go to next step.
Check cylinder No. 3 injector driver circuit between 10-pin injector harness connector and PCM for an open circuit. Repair as necessary. After repairs, go to step 16 .
Locate and repair short to ground in fuel injector driver circuit between PCM and 10-pin injector harness connector. After repairs, go to step 16 .
Replace PCM. Program replacement PCM using required equipment. After repairs, go to next step.
Using scan tool, clear DTCs. Turn ignition off for 15 seconds. Start engine and operate vehicle with the FAILURE RECORDS conditions. Check for DTCs. If this DTC is set, go to step 2 . If this DTC is not set, system is okay.

DTC P0203: INJECTOR NO. 3 CONTROL CIRCUIT (3.5L "W" BODY)

Note. For circuit reference, see appropriate wiring diagram in WIRING DIAGRAMS article.

PCM will enable an injector on intake stroke of each cylinder. Ignition voltage is supplied directly to fuel injectors. PCM controls each injector by grounding control circuit via an internal driver.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-introduction__on-board-diagnostic-obd-system-check) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Start engine and let idle. Using scan tool, monitor injector circuit status for cylinder No. 3. If scan tool does not indicate a circuit fault, see «DIAGNOSTIC AIDS»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p0135-p0204) . If scan tool does indicates a circuit fault, go to next step.
If an entire bank of cylinders is inoperative, go to next step. If an entire bank of cylinders is not inoperative, go to step 6 .
Inspect fuel injector fuses located in underhood fuse block assembly. If fuses are okay, go to next step. If either fuse is open, go to step 11 .
Turn ignition off. Disconnect No. 3 fuel injector harness connector. Turn ignition on. Measure voltage between ground and ignition feed circuit at No. 3 fuel injector harness connector. If battery voltage is present, go to next step. If battery voltage is not present, go to step 12 .
Connect injector test light to No. 3 injector harness connector. Crank engine. If test light flashes, go to step 18 . If test light does not flash, go to next step.
Turn ignition off. Disconnect PCM harness connector. Measure resistance in injector control circuit between injector No. 3 and PCM. If resistance is 5 ohms or less, go to next step. If resistance is not 5 ohms or less, go to step 13 .
Check for continuity between injector control circuit and ground. If continuity is present, go to step 14 . If continuity is not present, go to next step.
Turn ignition on, with engine off. Check for voltage on injector control circuit. If any voltage is present, go to step 15 . If no voltage is present, go to next step.
Turn ignition off. Disconnect all fuel injectors. Check for continuity between fuel injector control circuits. If continuity is present between any circuits, go to step 16 . If continuity is not present between any circuit, go to step 20 .
Check for short to ground in injector ignition feed circuit. Repair as necessary. After repairs, go to step 22 . If circuit is okay, go to step 17 .
Repair open or high resistance in injector ignition feed circuit. After repairs, go to step 22 .
Repair open or high resistance in injector control circuit. After repairs, go to step 22 .
Repair short to ground in injector control circuit. After repairs, go to step 22 .
Repair short to voltage in injector control circuit. After repairs, go to step 22 .
Repair injector control circuits that are shorted together. After repairs, go to step 22 .
Check fuel injector. Perform fuel injector coil test. See FUEL SYSTEM in appropriate SYSTEM & COMPONENT TESTING article. Repair as necessary. After repairs, go to step 22 .
Check for poor connections and improper terminal tension at fuel injector. Repair as necessary. After repairs, go to step 22 . If connections and terminal tension is okay, go to next step.
Replace fuel injector. After repairs, go to step 22 .
Check for poor connections and improper terminal tension at PCM. Repair as necessary. After repairs, go to step 22 . If connections and terminal tension is okay, go to next step.
Replace PCM. Program replacement PCM using required equipment. After repairs, go to next step.
Using scan tool, clear DTCs. Turn ignition off for 15 seconds. Start engine and operate vehicle. Check for DTCs. If DTC P0201 is set, go to step 2 . If DTC P0201 is not set, go to next step.
If other DTCs were present during OBD system check and have not been diagnosed, go to applicable DTC. If no other DTCs are present, system is okay.

Check for damaged wiring harness. If harness appears to be okay, observe scan tool while moving related connectors and wiring harnesses. A change in scan tool display may help to locate fault.

DTC P0203: INJECTOR NO. 3 CONTROL CIRCUIT (3.8L "C", "F", "G", "H" & "W" BODIES)

Note. For circuit reference, see appropriate wiring diagram in WIRING DIAGRAMS article.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-introduction__on-board-diagnostic-obd-system-check) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Start and operate engine at idle. Using scan tool, monitor SPECIFIC DTC. If scan tool indicates that this DTC failed this ignition cycle, go to step 4 . If scan does not indicate that this DTC failed this ignition cycle, go to next step.
Turn ignition on, engine off. Using scan tool, review and record FAILURE RECORDS data. Operate vehicle in fail conditions parameter. If scan tool indicates that this DTC failed this ignition cycle, go to next step. If scan tool does not indicate that this DTC failed this ignition cycle, see «DIAGNOSTIC AIDS»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p0135-p0204) .
Turn ignition off. Disconnect PCM harness connector. Turn ignition on, with engine off. Measure voltage between cylinder No. 3 fuel injector control circuit and ground. If voltage is near battery voltage, go to next step. If voltage is not near battery voltage, go to step 9 .
Check fuel injectors. Perform fuel injector coil test. See FUEL SYSTEM in appropriate SYSTEM & COMPONENT TESTING article. If injectors are okay, go to next step. If injectors are not okay, go to step 17 .
Turn ignition off. Disconnect cylinder No. 3 injector connector. Turn ignition on. Measure voltage between ground and fuel injector No. 3 control circuit at PCM harness connector. If voltage is near zero volts, go to next step. If voltage is not near zero volts, go to step 16 .
Check for intermittent open in ignition feed circuit in harness between fuse and injector No. 3. Check for intermittent open in injector No. 3 control circuit between PCM and injector. Repair as necessary. After repairs, go to step 19 . If circuits are okay, go to next step.
Check for poor terminal connections at fuel injector No. 3 connector and injector No. 3 connection at PCM harness connector. Repair as necessary. After repairs, go to step 19 . If connections are okay, go to step 18 .
Turn ignition off. Disconnect injector No. 3. Turn ignition on. Measure voltage between ground and ignition feed circuit at injector No. 3 connector. If battery voltage is present, go to next step. If battery voltage is not present, go to step 14 .
Using a test light connected to battery positive, probe test light to injector No. 3 control circuit. If test light illuminates, go to step 15 . If test light does not illuminate, go to next step.
Turn ignition off. Using a fused jumper wire, jumper injector No. 3 control circuit and ignition feed circuit at injector connector. Turn ignition on. Using test light connected to ground, probe injector No. 3 control circuit at PCM harness connector. If test light illuminates, go to next step. If test light does not illuminate, go to step 13 .
Check for poor terminal contact at injector No. 3 connector. Repair as necessary. After repairs, go to step 19 . If connection is okay, go to step 17 .
Locate and repair open in injector No. 3 control circuit. After repairs, go to step 19 .
Locate and repair open or short to ground in injector No. 3 ignition feed circuit. After repairs, go to step 19 .
Locate and repair short to ground in injector No. 3 control circuit. After repairs, go to step 19 .
Locate and repair short to voltage in injector No. 3 control circuit. After repairs, go to step 19 .
Replace faulty injector. After repairs, go to step 19 .
Replace PCM. Program replacement PCM using required equipment. After repairs, go to next step.
Using scan tool, clear DTCs. Turn ignition off for 15 seconds. Start engine and operate vehicle with the FAILURE RECORDS conditions. Check for DTCs. If this DTC is set, go to step 2 . If this DTC is not set, system is okay.

DTC P0203: INJECTOR NO. 3 CONTROL CIRCUIT (4.0L "G" BODY & 4.6L "E" & "K" BODIES)

Note. For circuit reference, see appropriate wiring diagram in WIRING DIAGRAMS article.

The PCM contains a General Field Effect Transistor Driver (GFD) that controls the 8 fuel injector drivers. The GFD is used to determine if there is a problem with any of the fuel injector circuits. The GFD has a fault line for each injector. The fault line goes high when an open, short to ground, or short to voltage is noticed in an injector circuit. DTC P0203 will set when the fault line for an injector is high.

For duplication of DTC, ensure DTCs P0560 and P1376 are not set, and ignition voltage is 10-16 volts.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-introduction__on-board-diagnostic-obd-system-check) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Turn ignition on. Using scan tool, check if DTCs P0202, P0205 and P0208 are also present. If these DTCs are present, diagnose using DTC P0202 test. If these DTCs are not present, go to next step.
Using scan tool, select DTC INFO, and then LAST TST. FAIL mode. If this DTC failed its last test, go to step 5 . If this DTC does not show that it failed its last test, go to next step.
Clear DTCs and operate vehicle until DTC P0203 resets. If DTC P0203 resets, go to next step. If DTC P0203 does not reset, fault is not present.
Turn ignition off. Disconnect injector No. 3 harness connector. Turn ignition on. Measure voltage between injector No. 3 harness connector terminal "A" and ground. If voltage is 10 volts or greater, go to next step. If voltage is not 10 volts or greater, go to step 13 .
Reconnect injector No. 3 harness connector. Store fluid life reading as indicated on scan tool. Turn ignition off for 30 seconds, and then disconnect PCM harness connector C2. Turn ignition on. Measure voltage between ground and PCM harness connector C2, terminal No. 12. If voltage is greater than 10 volts, go to next step. If voltage is not greater than 10 volts, go to step 10 .
Disconnect injector No. 3 harness connector. Measure resistance between injector terminals "A" and "B". If resistance is greater than 8 ohms, go to next step. If resistance is not greater than 8 ohms, go to step 18 .
Measure voltage between ground and injector No. 3 harness connector terminal "B". If voltage is 0.1 volt or less, go to next step. If voltage is not 0.1 volt or less, go to step 14 .
Check terminal contact at PCM harness connector C2. Repair as necessary. If terminal contact is okay, go to step 19 .
Turn ignition off. Reconnect PCM harness connector C2. Disconnect fuel rail harness connector. Turn ignition on. Measure voltage between injector harness terminal "D" and ground. If voltage is less than 10 volts, go to next step. If voltage is not less than 10 volts, go to step 15 .
Disconnect injector No. 3 harness connector. Measure resistance between injector terminal "D" and ground. If resistance is greater than 10,000 ohms, go to next step. If resistance is not greater than 10,000 ohms, go to step 16 .
Measure resistance between injector terminals "A" and "B". If resistance is greater than 25 ohms, go to step 18 . If resistance is not greater than 25 ohms, go to step 17 .
Repair open in circuit between splice and injector No. 3.
Repair short to voltage in injector No. 3 control circuit.
Repair open or short to ground in injector No. 3 control circuit.
Repair short to ground in injector No. 3 control circuit.
Repair open in injector No. 3 control circuit.
Replace fuel injector.
Replace PCM. Program replacement PCM using required equipment.

DTC P0204: INJECTOR NO. 4 CONTROL CIRCUIT (3.0L "V" BODY)

Note. For circuit reference, see appropriate wiring diagram in WIRING DIAGRAMS article.

ECM will enable an injector on intake stroke of each cylinder. Ignition voltage is supplied directly to fuel injectors. ECM controls each injector by grounding control circuit via an internal driver.

Primary function of driver is to supply ground for component being controlled. Each driver has a fault line which is monitored by ECM. When ECM is commanding a component on, voltage of control circuit should be low (near zero volts). When ECM is commanding control circuit to component off, voltage potential of circuit should be high (near battery voltage). If fault detection circuit senses a voltage other than what is expected, DTC P0204 will set.

For duplication of DTC, ensure ignition voltage is 7.5-15 volts, and engine speed is greater than 80 RPM.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-introduction__on-board-diagnostic-obd-system-check) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Start and idle engine. Using scan tool, monitor misfire current cylinder No. 4. If counter is incrementing, go to next step. If counter is not incrementing, see «DIAGNOSTIC AIDS»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p0135-p0204) .
Turn ignition off. Disconnect main fuel injector connector. Turn ignition on, with engine off. Using test light connected to battery positive, probe injector No. 4 harness connector control circuit (ECM side). If test light illuminates, go to next step. If test light does not illuminate, go to step 6 .
Turn ignition off. Disconnect ECM harness connector located in engine compartment relay center. If test light is illuminated, go to step 11 . If test light does not illuminate, go to next step.
Turn ignition on, with engine off. Using test light connected to ground, probe injector No. 4 harness connector control circuit (ECM side). If test light illuminates, go to step 12 . If test light does not illuminate, go to step 15 .
Crank engine. If test light flashes about once per second, go to step 8 . If test light does not flash about once per second, go to next step.
Turn ignition off. Disconnect ECM harness connector located in engine compartment relay center. Using DVOM, check harness continuity of injector No. 4 control circuit between main injector and ECM harness connectors. If continuity is present, go to step 14 . If continuity is not present, go to step 10 .
Turn ignition off. Using a jumper wire, reconnect switched battery feed circuit in male half of main injector harness connector to switched battery feed circuit in female half of main injector harness connector. Using test light connected to ground, probe injector No. 4 harness connector control circuit (injector side). Turn ignition on, with engine off. If test light illuminates, go to step 13 . If test light does not illuminate, go to next step.
Check for poor connections and terminal tension at fuel injector harness connector or at main injector connector. Check injector control circuit for open, short to ground, or short to voltage between injector and main injector connector. Check for open in switched battery feed circuit between injector and wiring splice. Repair as necessary. After repairs, go to step 16 . If connections, terminals and circuits are okay, go to step 13 .
Repair open or high resistance in injector control circuit. After repairs, go to step 16 .
Repair short to ground in injector control circuit. After repairs, go to step 16 .
Repair short to voltage in injector driver circuit. After repairs, go to step 16 .
Replace fuel injector. After repairs, go to step 16 .
Check for poor connections and terminal tension at ECM harness connector. Repair as necessary. After repairs, go to step 16 . If connections and terminals are okay, go to next step.
Replace ECM. New ECM must be programmed with theft deterrent module frequency code currently on vehicle. After repairs, go to next step.
Using scan tool, clear DTCs. Turn ignition off for 15 seconds. Start engine and operate vehicle. Check for DTCs. If DTC P0204 is set, go to step 2 . If DTC P0204 is not set, go to next step.
If other DTCs were present during OBD system check and have not been diagnosed, go to applicable DTC. If no other DTCs are present, system is okay.

Check for damaged wiring harness. If harness appears to be okay, observe scan tool while moving related connectors and wiring harnesses. A change in scan tool display may help to locate fault.

DTC P0204: INJECTOR NO. 4 CONTROL CIRCUIT (3.1L "N" & "W" BODIES & 3.4L "N" BODY & "U" SERIES)

Note. For circuit reference, see appropriate wiring diagram in WIRING DIAGRAMS article.

For duplication of DTC, ensure DTCs P0560 and P1376 are not set, and ignition voltage is 10-16 volts.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-introduction__on-board-diagnostic-obd-system-check) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Start and operate engine at idle. Using scan tool, monitor SPECIFIC DTC. If scan tool indicates that this DTC failed this ignition cycle, go to step 4 . If scan does not indicate that this DTC failed this ignition cycle, go to next step.
Turn ignition on, engine off. Using scan tool, review and record FAILURE RECORDS data. Operate vehicle in failure conditions parameter. If scan tool indicates that this DTC failed this ignition cycle, go to next step. If scan tool does not indicate that this DTC failed this ignition cycle, see «DIAGNOSTIC AIDS»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p0135-p0204) .
Using scan tool, enter OUTPUT DRIVER DATA menu. If scan tool indicates that cylinder No. 4 injector circuit is STUCK HIGH, go to step 6 . If scan tool does not indicate that cylinder No. 4 injector circuit is STUCK HIGH, go to next step.
If scan tool indicates that cylinder No. 4 injector circuit is STUCK LOW, go to step 10 . If scan tool does not indicate that cylinder No. 4 injector circuit is STUCK LOW, see «DIAGNOSTIC AIDS»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p0135-p0204) .
Turn ignition off. Disconnect 10-pin fuel injector harness connector. Crank engine. While cranking engine, if scan tool indicates that cylinder No. 4 injector circuit is STUCK HIGH, go to next step. If scan tool does not indicate that cylinder No. 4 injector circuit is STUCK HIGH, go to step 9 .
Turn ignition off. Disconnect PCM harness connector. Turn ignition on, engine off. Measure voltage between cylinder No. 4 fuel injector control circuit and ground. If voltage is near battery voltage, go to next step. If voltage is not near battery voltage, go to step 15 .
Locate and repair short to voltage in cylinder No. 4 fuel injector control circuit. After repairs, go to step 16 .
If scan tool indicates that No. 4 injector control circuit is STUCK LOW, check affected fuel injector. Perform fuel injector coil test. See FUEL SYSTEM in appropriate SYSTEM & COMPONENT TESTING article.
Disconnect 10-pin fuel injector harness connector. Using a test light connected to battery positive, probe injector No. 4 control circuit at PCM side of 10-pin connector. If test light illuminates, go to next step. If test light does not illuminate, go to step 12 .
Disconnect PCM harness connector. Using a test light connected to battery positive, probe injector No. 4 control circuit at PCM harness connector. If test light illuminates, go to step 14 . If test light does not illuminate, go to step 15 .
With test light still connected, crank engine. If test light flashes, check affected fuel injector. Perform fuel injector coil test. See FUEL SYSTEM in appropriate SYSTEM & COMPONENT TESTING article. If test light does not flash, go to next step.
Check cylinder No. 4 injector driver circuit between 10-pin injector connector and PCM for an open circuit. Repair as necessary. After repairs, go to step 16 .
Locate and repair short to ground in fuel injector driver circuit between PCM and 10-pin injector connector. After repairs, go to step 16 .
Replace PCM. Program replacement PCM using required equipment. After repairs, go to next step.
Using scan tool, clear DTCs. Turn ignition off for 15 seconds. Start engine and operate vehicle with the FAILURE RECORDS conditions. Check for DTCs. If this DTC is set, go to step 2 . If this DTC is not set, system is okay.

DTC P0204: INJECTOR NO. 4 CONTROL CIRCUIT (3.5L "W" BODY)

Note. For circuit reference, see appropriate wiring diagram in WIRING DIAGRAMS article.

PCM will enable an injector on intake stroke of each cylinder. Ignition voltage is supplied directly to fuel injectors. PCM controls each injector by grounding control circuit via an internal driver.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-introduction__on-board-diagnostic-obd-system-check) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Start engine and let idle. Using scan tool, monitor injector circuit status for cylinder No. 4. If scan tool does not indicate a circuit fault, see «DIAGNOSTIC AIDS»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p0135-p0204) . If scan tool does indicates a circuit fault, go to next step.
If an entire bank of cylinders is inoperative, go to next step. If an entire bank of cylinders is not inoperative, go to step 6 .
Inspect fuel injector fuses located in underhood fuse block assembly. If fuses are okay, go to next step. If either fuse is open, go to step 11 .
Turn ignition off. Disconnect No. 4 fuel injector harness connector. Turn ignition on. Measure voltage between ground and ignition feed circuit at No. 4 fuel injector harness connector. If battery voltage is present, go to next step. If battery voltage is not present, go to step 12 .
Connect injector test light to No. 4 injector harness connector. Crank engine. If test light flashes, go to step 18 . If test light does not flash, go to next step.
Turn ignition off. Disconnect PCM harness connector. Measure resistance in injector control circuit between injector No. 4 and PCM. If resistance is 5 ohms or less, go to next step. If resistance is not 5 ohms or less, go to step 13 .
Check for continuity between injector control circuit and ground. If continuity is present, go to step 14 . If continuity is not present, go to next step.
Turn ignition on, with engine off. Check for voltage on injector control circuit. If any voltage is present, go to step 15 . If no voltage is present, go to next step.
Turn ignition off. Disconnect all fuel injectors. Check for continuity between fuel injector control circuits. If continuity is present between any circuits, go to step 16 . If continuity is not present between any circuit, go to step 20 .
Check for short to ground in injector ignition feed circuit. Repair as necessary. After repairs, go to step 22 . If circuit is okay, go to step 17 .
Repair open or high resistance in injector ignition feed circuit. After repairs, go to step 22 .
Repair open or high resistance in injector control circuit. After repairs, go to step 22 .
Repair short to ground in injector control circuit. After repairs, go to step 22 .
Repair short to voltage in injector control circuit. After repairs, go to step 22 .
Repair injector control circuits that are shorted together. After repairs, go to step 22 .
Check fuel injector. Perform fuel injector coil test. See FUEL SYSTEM in appropriate SYSTEM & COMPONENT TESTING article. Repair as necessary. After repairs, go to step 22 .
Check for poor connections and improper terminal tension at fuel injector. Repair as necessary. After repairs, go to step 22 . If connections and terminal tension is okay, go to next step.
Replace fuel injector. After repairs, go to step 22 .
Check for poor connections and improper terminal tension at PCM. Repair as necessary. After repairs, go to step 22 . If connections and terminal tension is okay, go to next step.
Replace PCM. Program replacement PCM using required equipment. After repairs, go to next step.
Using scan tool, clear DTCs. Turn ignition off for 15 seconds. Start engine and operate vehicle. Check for DTCs. If DTC P0201 is set, go to step 2 . If DTC P0201 is not set, go to next step.
If other DTCs were present during OBD system check and have not been diagnosed, go to applicable DTC. If no other DTCs are present, system is okay.

Check for damaged wiring harness. If harness appears to be okay, observe scan tool while moving related connectors and wiring harnesses. A change in scan tool display may help to locate fault.

DTC P0204: INJECTOR NO. 4 CONTROL CIRCUIT (3.8L "C", "F", "G", "H" & "W" BODIES)

Note. For circuit reference, see appropriate wiring diagram in WIRING DIAGRAMS article.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-introduction__on-board-diagnostic-obd-system-check) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Start and operate engine at idle. Using scan tool, monitor SPECIFIC DTC. If scan tool indicates that this DTC failed this ignition cycle, go to step 4 . If scan does not indicate that this DTC failed this ignition cycle, go to next step.
Turn ignition on, engine off. Using scan tool, review and record FAILURE RECORDS data. Operate vehicle in fail conditions parameter. If scan tool indicates that this DTC failed this ignition cycle, go to next step. If scan tool does not indicate that this DTC failed this ignition cycle, see «DIAGNOSTIC AIDS»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p0135-p0204) .
Turn ignition off. Disconnect PCM harness connector. Turn ignition on, engine off. Check voltage between cylinder No. 4 fuel injector control circuit and ground. If voltage reading is battery voltage, go to next step. If voltage reading is not battery voltage, go to step 9 .
Check fuel injectors. See appropriate SYSTEM & COMPONENT TESTING article. If injectors are okay, go to next step. If injectors are not okay, go to step 17 .
Turn ignition off. Disconnect cylinder No. 4 injector connector. Turn ignition on. Check voltage between ground and fuel injector No. 4 control circuit at PCM connector. If voltage reading is zero volts, go to next step. If voltage reading is not zero volts, go to step 16 .
Check for intermittent open in ignition feed circuit in harness between fuse and injector No. 4. Check for intermittent open in injector No. 4 control circuit between PCM and injector. Repair as necessary. After repairs, go to step 19 . If circuits are okay, go to next step.
Check for poor terminal connections at fuel injector No. 4 connector and injector No. 4 connection at PCM connector. Repair as necessary. After repairs, go to step 19 . If connections are okay, go to step 18 .
Turn ignition off. Disconnect injector No. 4. Turn ignition on. Check voltage between ground and ignition feed circuit at injector No. 4 connector. If battery voltage is present, go to next step. If battery voltage is not present, go to step 14 .
Using a test light connected to battery voltage, probe test light to injector No. 4 control circuit. If test light illuminates, go to step 15 . If test light does not illuminate, go to next step.
Turn ignition off. Using a fused jumper wire, jumper injector No. 4 control circuit and ignition feed circuit at injector connector. Turn ignition on. Using test light connected to ground, probe injector No. 4 control circuit at PCM connector. If test light illuminates, go to next step. If test light does not illuminate, go to step 13 .
Check for poor terminal contact at injector No. 4 connector. Repair as necessary. After repairs, go to step 19 . If connection is okay, go to step 17 .
Locate and repair open in injector No. 4 control circuit. After repairs, go to step 19 .
Locate and repair open or short to ground in injector No. 4 ignition feed circuit. After repairs, go to step 19 .
Locate and repair short to ground in injector No. 4 control circuit. After repairs, go to step 19 .
Locate and repair short to voltage in injector No. 4 control circuit. After repairs, go to step 19 .
Replace faulty injector. After replacing injector, go to step 19 .
Replace PCM. Program replacement PCM using required equipment. After replacing PCM, go to next step.
Using scan tool, clear DTCs. Turn ignition off for 15 seconds. Start engine and operate vehicle with the FAILURE RECORDS conditions. Check for DTCs. If this DTC is set, go to repeat step 2 . If this DTC is not set, system is okay.

DTC P0204: INJECTOR NO. 4 CONTROL CIRCUIT (4.0L "G" BODY & 4.6L "E" & "K" BODIES)

Note. For circuit reference, see appropriate wiring diagram in WIRING DIAGRAMS article.

The PCM contains a General Field Effect Transistor Driver (GFD) that controls the 8 fuel injector drivers. The GFD is used to determine if there is a problem with any of the fuel injector circuits. The GFD has a fault line for each injector. The fault line goes high when an open, short to ground, or short to voltage is noticed in an injector circuit. DTC will set when the fault line for an injector is high. For duplication of DTC, ensure DTCs P0560 and P1376 are not set, and ignition voltage is 10-16 volts.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(/cadillac/escalade/gmt400-1998-2000/remont/testing-diagnostics/#engine-control-system-tests-wcodes-introduction__on-board-diagnostic-obd-system-check) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Turn ignition on. Using scan tool, check if DTCs P0201, P0206 and P0207 are also present. If these DTCs are present, diagnose using DTC P0201 test. If these DTCs are not present, go to next step.
Using scan tool, select DTC INFO then LAST TST. FAIL mode. If this DTC failed its last test, go to step 5 . If this DTC does not show that it failed its last test, go to next step.
Clear DTCs and operate vehicle until DTC P0204 resets. If DTC P0204 resets, go to next step. If DTC P0204 does not reset, fault is not present.
Turn ignition off. Disconnect injector No. 4 harness connector. Turn ignition on. Check voltage between injector No. 4 harness connector terminal "A" and ground. If voltage reading is 10 volts or greater, go to next step. If voltage reading is not 10 volts or greater, go to step 13 .
Reconnect injector No. 4 harness connector. Store fluid life reading as indicated on scan tool. Turn ignition off for 30 seconds, then disconnect PCM harness connector C2. Turn ignition on. Check voltage between PCM harness connector C2 terminal No. 13 and ground. If voltage reading is greater than 10 volts, go to next step. If voltage reading is not greater than 10 volts, go to step 10 .
Disconnect injector No. 4 harness connector. Check resistance between injector terminals "A" and "B". If resistance is greater than 8 ohms, go to next step. If resistance is not greater than 8 ohms, go to step 18 .
Check voltage between injector No. 4 harness connector terminal "B". If voltage reading is 0.1 volt or less, go to next step. If voltage reading is not 0.1 volt or less, go to step 14 .
Check terminal contact at PCM connector C2. Repair as necessary. If terminal contact is okay, go to step 19 .
Turn ignition off. Reconnect PCM connector C2. Disconnect fuel rail harness connector. Turn ignition on. Measure voltage between injector harness terminal "E" and ground. If voltage reading is less than 10 volts, go to next step. If voltage reading is not less than 10 volts, go to step 15 .
Disconnect injector No. 4 harness connector. Check resistance between injector terminal "A" and ground. If resistance is greater than 10,000 ohms, go to next step. If resistance is not greater than 10,000 ohms, go to step 16 .
Check resistance between injector terminals "A" and "B". If resistance is greater than 25 ohms, go to step 18 . If resistance is not greater than 25 ohms, go to step 17 .
Repair open in circuit between splice and injector No. 4.
Repair short to voltage between injector harness connector and PCM harness connector.
Repair open or short to ground in circuit between fuel rail connector and injector No. 4.
Repair short to ground in circuit between fuel rail connector and injector No. 4.
Repair open in circuit between fuel rail connector and injector No. 4.
Replace fuel injector.
Replace PCM. Program replacement PCM using required equipment.

Engine Control System - Tests W/codes - DTC p0135-p0204 Cadillac Escalade GMT400

MODEL IDENTIFICATION

DTC P0135: HO2S HEATER CIRCUIT-BANK 1, SENSOR 1 (3.0L "V" BODY)

Circuit Description

Diagnostic Procedures

Diagnostic Aids

DTC P0135: HO2S HEATER CIRCUIT-SENSOR 1 (3.1L "N" & "W" BODIES & 3.4L "N" BODY & "U" SERIES)

DTC P0135: HO2S HEATER CIRCUIT-SENSOR 1 (3.5L "W" BODY)

DTC P0135: HO2S HEATER CIRCUIT-SENSOR 1 (3.8L "C", "F", "G", "H" & "W" BODIES)

DTC P0135: HO2S HEATER CIRCUIT-BANK 1, SENSOR 1 (4.0L "G" BODY & 4.6L "E" & "K" BODIES)

DTC P0135: HO2S HEATER CIRCUIT BANK 1, SENSOR 1 (4.3L, 5.0L, 5.7L & 7.4L "C", "G", "K", "L", "M", "P", "S" & "T" SERIES)

DTC P0135: HO2S HEATER CIRCUIT-BANK 1, SENSOR 1 (4.8L, 5.3L & 6.0L "C" & "K" SERIES)

DTC P0135: HO2S HEATER CIRCUIT-BANK 1, SENSOR 1 (5.7L "F" & "Y" BODIES)

DTC P0136: HO2S CIRCUIT-BANK 1, SENSOR 2 (3.0L "V" BODY)

DTC P0137: HO2S CIRCUIT-LOW VOLTAGE-SENSOR 2 (1.9L SATURN)

DTC P0137: HO2S CIRCUIT-LOW VOLTAGE-SENSOR 2 (2.2L "J" BODY, 2.2L "S" SERIES & 2.4L "J" & "N" BODIES)

DTC P0137: HO2S CIRCUIT-LOW VOLTAGE-SENSOR 2 (3.1L "N" & "W" BODIES & 3.4L "N" BODY & "U" SERIES)

DTC P0137: HO2S CIRCUIT-LOW VOLTAGE-SENSOR 2 (3.8L "C", "F", "G", "H" & "W" BODIES)

DTC P0137: HO2S CIRCUIT-LOW VOLTAGE-BANK 1, SENSOR 2 (4.8L, 5.3L & 6.0L "C" & "K" SERIES & 5.7L "F" & "Y" BODIES)

DTC P0137: HO2S CIRCUIT-LOW VOLTAGE-BANK 1, SENSOR 2 (5.0L, 5.7L & 7.4L "C", "G", "K" & "P" SERIES)

DTC P0138: HO2S CIRCUIT-VOLTAGE HIGH-SENSOR 2 (1.9L SATURN)

DTC P0138: HO2S CIRCUIT-VOLTAGE HIGH-SENSOR 2 (2.2L "J" BODY, 2.2L "S" SERIES & 2.4L "J" & "N" BODIES)

DTC P0138: HO2S CIRCUIT-HIGH VOLTAGE-BANK 1, SENSOR 2 (3.0L "V" BODY)

DTC P0138: HO2S CIRCUIT-HIGH VOLTAGE-SENSOR 2 (3.1L "N" & "W" BODIES & 3.4L "N" BODY & "U" SERIES)

DTC P0138: HO2S CIRCUIT-HIGH VOLTAGE-SENSOR 2 (3.8L "C", "F", "G", "H" & "W" BODIES)

DTC P0138: HO2S CIRCUIT-HIGH VOLTAGE-BANK 1, SENSOR 2 (4.3L "C" & "K" SERIES)

DTC P0138: HO2S CIRCUIT-HIGH VOLTAGE-BANK 1, SENSOR 2 (4.8L, 5.3L & 6.0L "C" & "K" SERIES)

DTC P0138: HO2S CIRCUIT-HIGH VOLTAGE-BANK 1, SENSOR 2 (5.0L, 5.7L & 7.4L "C", "G", "K" & "P" SERIES)

DTC P0138: HO2S CIRCUIT-HIGH VOLTAGE-BANK 1, SENSOR 2 (5.7L "F" & "Y" BODIES)

DTC P0139: HO2S CIRCUIT-SLOW RESPONSE-BANK 1, SENSOR 2 (3.0L "V" BODY)

DTC P0140: HO2S CIRCUIT-INSUFFICIENT ACTIVITY-SENSOR 2 (1.9L SATURN)

DTC P0140: HO2S CIRCUIT-INSUFFICIENT ACTIVITY-SENSOR 2 (2.2L "J" BODY, 2.2L "S" SERIES & 2.4L "J" & "N" BODIES)

DTC P0140: HO2S CIRCUIT-INSUFFICIENT ACTIVITY-BANK 1, SENSOR 2 (3.0L "V" BODY)

DTC P0140: HO2S CIRCUIT-INSUFFICIENT ACTIVITY-SENSOR 2 (3.1L "N" & "W" BODIES & 3.4L "N" BODY & "U" SERIES)

DTC P0140: HO2S CIRCUIT-INSUFFICIENT ACTIVITY-SENSOR 2 (3.5L "W" BODY)

DTC P0140: HO2S CIRCUIT-INSUFFICIENT ACTIVITY-SENSOR 2 (3.8L "C", "F", "G", "H" & "W" BODIES)

DTC P0140: HO2S CIRCUIT-INSUFFICIENT ACTIVITY-BANK 1, SENSOR 2 (4.3L, 5.0L, 5.7L & 7.4L "C", "G", "K" & "P" SERIES)

DTC P0140: HO2S CIRCUIT-INSUFFICIENT ACTIVITY-BANK 1, SENSOR 2 (4.8L, 5.3L & 6.0L "C" & "K" SERIES & 5.7L "F" & "Y" BODIES)

DTC P0141: HO2S HEATER CIRCUIT-SENSOR 2 (1.9L SATURN)

DTC P0141: HO2S HEATER CIRCUIT-SENSOR 2 (2.2L "J" BODY, 2.2L "S" SERIES & 2.4L "J" & "N" BODIES)

DTC P0141: HO2S HEATER CIRCUIT-BANK 1, SENSOR 2 (3.0L "V" BODY)

DTC P0141: HO2S HEATER CIRCUIT-SENSOR 2 (3.1L "N" & "W" BODIES & 3.4L "N" BODY & "U" SERIES)

DTC P0141: HO2S 2 HEATER CIRCUIT-SENSOR 2 (3.8L "C", "F", "G", "H" & "W" BODIES)

DTC P0141: HO2S HEATER CIRCUIT-BANK 1, SENSOR 2 (4.3L, 5.0L, 5.7L & 7.4L "C", "G", "K" & "P" SERIES)

DTC P0141: HO2S HEATER CIRCUIT-BANK 1, SENSOR 2 (4.8L, 5.3L, & 6.0L "C" & "K" SERIES & 5.7L "F" & "Y" BODIES)

DTC P0143: HO2S CIRCUIT-LOW VOLTAGE-BANK 1, SENSOR 3 (3.8L "F" BODY)

DTC P0143: HO2S CIRCUIT-LOW VOLTAGE-BANK 1, SENSOR 3 (4.0L "G" BODY & 4.6L "E" & "K" BODIES)

DTC P0143: HO2S CIRCUIT-LOW VOLTAGE-BANK 1, SENSOR 3 (4.3L, 5.0L & 5.7L "C", "G", "K", "L", "M", "P", "S" & "T" SERIES)

DTC P0144: HO2S CIRCUIT-HIGH VOLTAGE-BANK 1, SENSOR 3 (3.8L "F" BODY)

DTC P0144: HO2S CIRCUIT-HIGH VOLTAGE-BANK 1, SENSOR 3 (4.0L "G" BODY & 4.6L "E" & "K" BODIES)

DTC P0144: HO2S CIRCUIT-HIGH VOLTAGE-BANK 1, SENSOR 3 (4.3L, 5.0L & 5.7L "C", "G", "K", "L", "M", "P", "S" & "T" SERIES)

DTC P0146: HO2S CIRCUIT-INSUFFICIENT ACTIVITY-BANK 1, SENSOR 3 (3.8L "F" BODY)

DTC P0146: HO2S CIRCUIT-INSUFFICIENT ACTIVITY-BANK 1, SENSOR 3 (4.0L "G" BODY & 4.6L "E" & "K" BODIES)

DTC P0146: HO2S CIRCUIT-INSUFFICIENT ACTIVITY-BANK 1, SENSOR 3 (4.3L, 5.0L & 5.7L "C", "G", "K, "L", "M", "P", "S" & "T" SERIES)

DTC P0147: HO2S HEATER CIRCUIT-BANK 1, SENSOR 3 (3.8L "F" BODY)

DTC P0147: HO2S HEATER CIRCUIT-BANK 1, SENSOR 3 (4.0L "G" BODY & 4.6L "E" & "K" BODIES)

DTC P0147: HO2S HEATER CIRCUIT BANK 1, SENSOR 3 (4.3L, 5.0L & 5.7L "C", "G", "K", "L", "M", "P", "S" & "T" SERIES)

DTC P0150: HO2S CIRCUIT-BANK 2, SENSOR 1 (3.0L "V" BODY)

DTC P0151: HO2S CIRCUIT VOLTAGE LOW BANK 2, SENSOR 1 (3.0L "V" BODY)

DTC P0151: HO2S CIRCUIT VOLTAGE LOW BANK 2, SENSOR 1 (3.8L "F" BODY)

DTC P0151: HO2S CIRCUIT-LOW VOLTAGE-BANK 2, SENSOR 1 (4.0L "G" BODY & 4.6L "E" & "K" BODIES)

DTC P0151: HO2S CIRCUIT-LOW VOLTAGE-BANK 2, SENSOR 1 (4.3L, 5.0L, 5.7L & 7.4L "C", "G", "K", "L", "M", "P", "S" & "T" SERIES)

DTC P0151: HO2S CIRCUIT-LOW VOLTAGE-BANK 2, SENSOR 1 (4.8L, 5.3L & 6.0L "C" & "K" SERIES & 5.7L "F" & "Y" BODIES)

DTC P0152: HO2S CIRCUIT-HIGH VOLTAGE-BANK 2, SENSOR 1 (3.0L "V" BODY)

DTC P0152: HO2S CIRCUIT-HIGH VOLTAGE-BANK 2, SENSOR 1 (3.8L "F" BODY)

DTC P0152: HO2S CIRCUIT-HIGH VOLTAGE-BANK 2, SENSOR 1 (4.0L "G" BODY & 4.6L "E" & "K" BODIES)

DTC P0152: HO2S CIRCUIT VOLTAGE HIGH BANK 2, SENSOR 1 (4.3L, 5.0L, 5.7L & 7.4L "C", "G", "K", "L", "M", "P", "S" & "T" SERIES)

DTC P0152: HO2S CIRCUIT-HIGH VOLTAGE-BANK 2, SENSOR 1 (4.8L, 5.3L & 6.0L "C" & "K" SERIES)

DTC P0152: HO2S CIRCUIT-HIGH VOLTAGE-BANK 2, SENSOR 1 (5.7L "F" & "Y" BODIES)

DTC P0153: HO2S CIRCUIT-SLOW RESPONSE-BANK 2, SENSOR 1 (3.8L "F" BODY)

DTC P0153: HO2S CIRCUIT-SLOW RESPONSE-BANK 2, SENSOR 1 (4.0L "G" BODY & 4.6L "E" & "K" BODIES)

DTC P0153: HO2S CIRCUIT-SLOW RESPONSE-BANK 2, SENSOR 1 (4.3L, 5.0L, 5.7L & 7.4L "C", "G", "K", "L", "M", "P", "S" & "T" SERIES)

DTC P0153: HO2S CIRCUIT-SLOW RESPONSE-BANK 2, SENSOR 1 (4.8L, 5.3L & 6.0L "C" & "K" SERIES & 5.7L "F" & "Y" BODIES)

DTC P0154: HO2S CIRCUIT-INSUFFICIENT ACTIVITY-BANK 2, SENSOR 1 (3.0L "V" BODY)

DTC P0154: HO2S CIRCUIT-INSUFFICIENT ACTIVITY-BANK 2, SENSOR 1 (3.8L "F" BODY)

DTC P0154: HO2S CIRCUIT-INSUFFICIENT ACTIVITY-BANK 2, SENSOR 1 (4.0L "G" BODY & 4.6L "E" & "K" BODIES)

DTC P0154: HO2S CIRCUIT-INSUFFICIENT ACTIVITY-BANK 2, SENSOR 1 (4.3L "L" & "M" SERIES)

DTC P0154: HO2S CIRCUIT-INSUFFICIENT ACTIVITY-BANK 2, SENSOR 1 (4.3L, 5.0L, 5.7L & 7.4L "C", "G", "K", "P", "S" & "T" SERIES)

DTC P0154: HO2S CIRCUIT-INSUFFICIENT ACTIVITY-BANK 2, SENSOR 1 (4.8L, 5.3L & 6.0L "C" & "K" SERIES & 5.7L "F" & "Y" BODIES)

DTC P0155: HO2S HEATER CIRCUIT-BANK 2, SENSOR 1 (3.0L "V" BODY)