Engine Control System - Tests W/codes - DTC p1537-u1193

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 P1537: A/C REQUEST CIRCUIT LOW VOLTAGE (4.0L "G" BODY)

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

Circuit Description

This diagnostic test indicates very low refrigerant pressure or an open low pressure switch/circuit by comparing the A/C request discrete line, which contains the low pressure switch, to the A/C-heater serial data A/C request status. If the A/C request line is low (no voltage present), while the A/C-heater serial data is requesting A/C operation, DTC will set.

Diagnostic Procedures

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(ref-132811-S27457185922002013000000) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Start and idle engine. Turn on A/C to maximum cool and maximum fan (high speed). Using scan tool in DTC mode, select DTC INFO then select FAIL THIS IGN. Wait one minute and check if DTC sets. If DTC sets, go to next step. If DTC does not set, fault is not present. See «DIAGNOSTIC AIDS»(/gmc/savana/i-1996-2002/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p1537-u1193__diagnostic-aids) .
Turn engine off. Disconnect A/C low pressure switch harness connector. Remove A/C compressor fuse or A/C clutch relay. Using scan tool in ENGINE 3 mode, select A/C REQUEST. Using a jumper wire, jumper A/C low pressure switch harness connector terminals. Start engine and turn A/C on. If scan tool displays YES, go to step 8 . If scan tool does not display YES, go to next step.
Reinstall fuse or relay. Remove jumper. With engine running and A/C on, check voltage between ground and A/C low pressure switch harness connector terminal "A". If voltage reading is 10.5 volts or greater, go to next step. If voltage reading is less than 10.5 volts, go to step 7 .
Store fluid life index as indicated on scan tool. Turn ignition off and wait 30 seconds, then disconnect PCM harness connector C1. Check resistance between ground and A/C low pressure switch circuit at harness connector. If resistance is less than 10,000 ohms, go to next step. If resistance is not less than 10,000 ohms, go to step 9 .
Check resistance of A/C low pressure switch circuit between PCM harness connector and switch harness connector terminals. If resistance is 5 ohms or less, go to step 14 . If resistance is not less than 5 ohms, go to step 10 .
With engine on and A/C on, check voltage to ground at A/C-heater programmer terminal D15 (Dark Green/White wire). If voltage reading is 10.5 volts or greater, go to step 11 . If voltage reading is not 10.5 volts or greater, go to step 13 .
Reinstall fuse or relay. Install A/C manifold gauges to A/C system, and note low side pressure. If low side pressure is greater than 38 psi (2.7 kg/cm 2 ), go to step 12 . If low side pressure is not greater than 38 psi (2.7 kg/cm 2 ), system pressure is low. Diagnose A/C-heater system. See appropriate AUTOMATIC A/C-HEATER SYSTEMS article in AIR CONDITIONING & HEATING.
Repair short to ground in A/C low pressure switch signal circuit.
Repair open in A/C low pressure switch signal circuit.
Repair open in A/C low pressure switch circuit to A/C-heater programmer.
Replace A/C low pressure switch.
Replace A/C-heater programmer.
Check terminal contacts for A/C low pressure switch at PCM harness connector C1. Repair as necessary. If terminal contact is okay, go to next step.
Replace PCM. Program replacement PCM using required equipment.

Diagnostic Aids

If fault is not present, operate vehicle with A/C manifold gauge connected and watch for low A/C system pressure with A/C on for an extended period. Whenever A/C request line is checked for voltage, engine must be running.

DTC P1538: A/C REQUEST CIRCUIT HIGH VOLTAGE (4.0L "G" BODY)

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

This test indicates if A/C request circuit is shorted to voltage. This is done by comparing the A/C request line to the serial data received from the A/C-heater programmer. If A/C is not requested by serial data and the A/C request line is high (voltage present), DTC will set.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(ref-132811-S27457185922002013000000) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Start and idle engine. Turn on A/C to maximum cool and maximum fan (high speed). Using scan tool in DTC mode, select DTC INFO then select FAIL THIS IGN. Wait one minute and check if DTC sets. If DTC sets, go to next step. If DTC does not set, fault is not present.
In ENGINE 3 mode, note A/C REQUEST display on scan tool. If scan tool displays YES, go to next step. If scan tool does not display yes, go to step 10 .
Disconnect A/C low pressure switch harness connector. In ENGINE 3 mode, select A/C REQUEST and note display on scan tool. If scan tool displays YES, go to step 6 . If scan tool does not display YES, go to next step.
Reconnect low pressure switch harness connector. Remove A/C fuse. In ENGINE 3 mode, note A/C REQUEST display on scan tool. If scan tool displays YES, go to step 7 . If scan tool does not display YES, go to step 9 .
Store fluid life index as indicated on scan tool. Turn ignition off and wait 30 seconds, then disconnect PCM harness connector C1. Turn ignition on. Check voltage between ground and A/C low pressure switch circuit at harness connector. If voltage reading is greater.5 volt, go to step 8 . If voltage reading is not greater than.5 volt, go to step 10 .
Repair short to ground in A/C low pressure switch circuit to A/C-heater programmer.
Repair short to voltage in circuit between A/C low pressure switch and PCM.
Replace A/C-heater (HVAC) programmer.
Replace PCM. Program replacement PCM using required equipment.

DTC P1539: A/C CLUTCH STATUS CIRCUIT VOLTAGE HIGH (5.7L "F" & "Y" BODIES)

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

When PCM detects that A/C has been requested, PCM will activate A/C clutch relay. When relay is activated, voltage should be present at both A/C compressor clutch and A/C clutch status terminal at PCM.

DTC will set if PCM detects voltage on A/C clutch status terminal when A/C has not been requested, if there is a short to voltage at any point in A/C status circuit, if A/C relay contacts are stuck or when voltage is detected on the A/C status circuit for greater than 15 seconds after PCM has disengaged the A/C relay.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(ref-132811-S27457185922002013000000) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Start and idle engine. Turn A/C off. Using scan tool, select ENGINE 1 DATA LIST and monitor A/C status display. If scan tool indicates A/C status as ON, go to step 4 . If scan tool does not indicate that A/C status as ON, 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 then enter this DTC. 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»(/gmc/savana/i-1996-2002/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p1537-u1193) .
Turn ignition off. Remove A/C clutch relay. Start and idle engine for about 30 seconds. Using scan tool, select DTC INFO, FAIL THIS IGN. If scan tool indicates that DTC P1539 failed, go to next step. If scan tool does not indicate that DTC P1539 failed, go to step 6 .
Repair A/C clutch status circuit for short to battery voltage. After repairs, go to step 7 .
Replace AC clutch relay. After replacing relay, go to next step.
Using scan tool, select DTC, CLEAR INFO function. Start and warm engine to normal operating temperature. Select DTC, SPECIFIC, then enter this DTC. 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, repeat step 2 .
Using scan tool, select CAPTURE INFO, REVIEW INFO function. If any undiagnosed DTC(s) are displayed, go to applicable DTC test.

A/C status circuit goes to A/C compressor clutch and to A/C clutch relay. Check all circuits going to these components.

DTC P1540: A/C SYSTEM-HIGH PRESSURE (4.0L "G" BODY)

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

This test detects an over-pressure condition in the A/C system. DTC will set if the high pressure switch opens, disabling the A/C clutch at least 10 times. This is designed to detect blockage in the A/C system. When DTC is set, the A/C clutch will be disabled for the ignition cycle.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(ref-132811-S27457185922002013000000) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Start engine and turn A/C on. Using scan tool in ENGINE 3 mode, note A/C HI PRESS. SW. display. If scan tool displays NORMAL, fault is not present. See «DIAGNOSTIC AIDS»(/gmc/savana/i-1996-2002/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p1537-u1193) . If scan tool does not display NORMAL, go to next step.
Turn engine off. Connect A/C manifold gauges. Start engine and turn A/C on. Monitor A/C high side pressure on A/C manifold gauges and monitor A/C HI PRESS. SW. display on scan tool. If scan tool displays HI PRESS. and high pressure side is greater than 430 psi (30 kg/cm 2 ), go to step 7 . If scan tool does not display HI PRESS. or if high pressure side is less than 430 psi (30 kg/cm 2 ), go to next step.
Turn ignition off. Disconnect A/C high pressure switch harness connector and PCM harness connector C1. Check terminal contact at both switch and PCM harness connectors. Repair as necessary. If terminal contacts are okay, go to next step.
Check for intermittent open in A/C high pressure switch signal and ground circuit. Repair as necessary. If circuits are okay, go to next step.
Replace A/C high pressure switch.
Repair cause of high A/C system pressure. See appropriate AUTOMATIC A/C-HEATER SYSTEMS article in AIR CONDITIONING & HEATING.

Use the FAILURE REC mode on scan tool and note conditions under which the DTC set. If A/C HIGH SIDE TEMP. was close to 189°F (87°C), then a high pressure condition probably occurred. If A/C HIGH SIDE TEMP. was low, then an intermittent open circuit or switch probably set the DTC.

DTC P1542: A/C SYSTEM HIGH PRESSURE/HIGH TEMPERATURE (4.0L "G" BODY)

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

This test detects an over-temperature or over-pressure condition in the A/C system. DTC will set if high pressure switch disables the A/C clutch and the high side temperature is above a threshold. Under extremely hot ambient conditions, a rapid cycling situation could occur as this DTC is set and cleared. To protect the A/C system, if this DTC continues to set and clear, a lower high side temperature will be used to clear the DTC. If after this occurs and a rapid cycling condition is detected for the third time, lower temperature is used to clear the DTC and re-enable the A/C clutch.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(ref-132811-S27457185922002013000000) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Turn ignition on. Using scan tool in DTC mode, select FAILURE REC and note the OUTSIDE AIR TEMP display when the DTC is set. If outside temperature is exceedingly hot, system is okay. See «DIAGNOSTIC AIDS»(/gmc/savana/i-1996-2002/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p1537-u1193) . If outside temperature is not that hot, diagnose A/C system. See appropriate AUTOMATIC A/C-HEATER SYSTEMS article in AIR CONDITIONING & HEATING.

This DTC is used for system protection during a high temperature/pressure condition. This condition could occur normally if sufficient cooling of the A/C system cannot occur due to high ambient temperature.

DTC P1545: A/C CLUTCH RELAY CONTROL CIRCUIT (3.0L "V" BODY)

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

DTC will run if battery voltage is 7.5-15.0 volts, vehicle speed is greater than 40 MPH and A/C clutch has been requested. DTC will set when ECM internal circuitry determines there is open or short in A/C compressor relay control circuit.

DTC will clear after 40 consecutive warm-up cycles in which no failures are reported by this diagnostic or any other non-essential related diagnostic, battery is disconnected or cleared by scan tool.

DTC P1546: A/C CLUTCH RELAY CIRCUIT FAULT (3.4L "U" SERIES)

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

Output Driver Modules (ODMs) are used by PCM to turn on many of the current-driven devices that are needed to control various engine and transmission functions. Each ODM is capable of controlling up to 7 separate outputs by applying ground to the device which PCM is commanding on. ODMs have the capability of diagnosing each output circuit individually. DTC will set when an improper voltage level has been detected on output circuit which controls the A/C compressor relay.

A history DTC will clear after 40 consecutive warm-up cycles have occurred without a malfunction. DTC will also clear when battery is disconnected or cleared by scan tool.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(ref-132811-S27457185922002013000000) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Turn ignition off. Disconnect PCM harness connector. Turn ignition on. Using DVOM, check voltage between ground and A/C relay control circuit on harness connector. If battery voltage is present, go to next step. If battery voltage is not present, go to step 6 .
Leave PCM harness connector disconnected. Set DVOM to 10-amp scale. Check current between A/C relay control circuit and ground. Monitor reading for about 2 minutes. If reading is 0.5-1.5 amps, go to next step. If reading is not 0.5-1.5 amps, go to step 13 .
Turn ignition off. Reconnect PCM harness connector. Remove A/C relay. Using a test light connected between relay connector cavities No. 85 and 86. Turn ignition on. Using scan tool, command A/C relay on and off. If test light flashes, see «DIAGNOSTIC AIDS»(/gmc/savana/i-1996-2002/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p1537-u1193) . If test light does not flash, go to next step.
Check for poor connections at PCM. If connections are faulty, go to step 22 . If connections are okay, go to step 21 .
Turn ignition off. Leave PCM harness connector disconnected. Remove A/C relay. Using a test light connected to ground, probe test light to relay connector cavity No. 86. If test light illuminates, go to next step. If test light does not illuminate, go to step 9 .
Check A/C relay control circuit for open or short to ground. If circuit is faulty, go to step 22 . If circuit is okay, go to next step.
Check for poor terminal connections at A/C relay connector. If connections are faulty, go to step 22 . If connections are okay, go to step 19 .
Turn ignition off. Remove ignition main relay. Using test light connected to ground, probe main relay connector cavity No. 87. If test light illuminates, go to next step. If test light does not illuminate, go to step 14 .
Connect a fused jumper wire between ignition main relay connector cavities No. 30 and 87. Connect test light between ground and A/C relay connector cavity No. 86. If test light illuminates, go to next step. If test light does not illuminate, go to step 15 .
Turn ignition on. Connect test light between ground and ignition main relay connector cavity No. 86. If test light illuminates, go to next step. If test light does not illuminate, go to step 16 .
Connect test light between battery voltage and ignition main relay connector cavity No. 85. If test light illuminates, go to step 20 . If test light does not illuminate, go to step 17 .
Turn ignition off. Leave PCM harness connector disconnected. Remove A/C relay. Connect a test light between ground and A/C relay control circuit. If test light illuminates, go to step 18 . If test light does not illuminate, go to step 19 .
Locate and repair open in battery feed circuit to ignition main relay connector cavity No. 87. After repairs, go to step 22 .
Locate and repair open in battery feed circuit to A/C relay connector cavity No. 86. After repairs, go to step 22 .
Locate and repair open in battery feed circuit to ignition main relay connector cavity No. 86. After repairs, go to step 22 .
Locate and repair open in ignition main relay ground circuit. After repairs, go to step 22 .
Locate and repair short to voltage in A/C relay control circuit. After repairs, go to step 22 .
Replace A/C relay. After replacing relay, go to step 22 .
Replace ignition relay. After replacing relay, go to step 22 .
Replace PCM. Program replacement PCM using required equipment. After replacing PCM, go to next step.
Using scan tool, select DTC, CLEAR INFO function. Start and warm engine to normal operating temperature. Select DTC, SPECIFIC, then enter this DTC. Operate vehicle within 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, repeat step 2 .

Using FREEZE FRAME and/or FAILURE RECORDS data mode may aid in locating an intermittent condition. If DTC cannot be duplicated, information included in FREEZE FRAME and/or FAILURE RECORDS data can be useful in determining how many miles since DTC set. FAIL COUNTER and PASS COUNTER can also be used to determine how many ignition cycles diagnostic reported a pass or a fail condition. To isolate when DTC failed, operate vehicle within same freeze frame conditions (RPM, load, vehicle speed, temperature, etc.).

DTC P1546: A/C CLUTCH RELAY CIRCUIT FAULT (3.8L "F"BODY)

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

Output Driver Modules (ODMs) are used by the PCM to turn on current-driven devices that are needed to control various engine and transaxle functions. Each ODM is capable of controlling up to 7 separate outputs by controlling the ground circuit when PCM is commanding ON. ODMs have the capability of diagnosing each output circuit individually.

DTC will also set when an improper voltage level has been detected on the output circuit which controls the A/C compressor relay and condition is present for at least 30 seconds.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(ref-132811-S27457185922002013000000) 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, command A/C relay on and off. If relay turns on and off as commanded, see «DIAGNOSTIC AIDS»(/gmc/savana/i-1996-2002/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p1537-u1193) . If relay does not turn on and off as commanded, go to next step.
Turn ignition off. Disconnect A/C relay. Turn ignition on. Using a test light connected to ground, probe relay coil feed circuit. If test light illuminates, go to next step. If test light does not illuminate, go to step 10 .
Connect test light between A/C relay control circuit and coil feed circuit. Using scan tool, command relay on and off. If test light turns on and off with each command, go to step 8 . If test light does not turn on and off with each command, go to next step.
If test light remains on with each command, go to step 7 . If test light does not remain on with each command, go to next step.
Check relay control circuit for short to voltage or open circuit. Repair as necessary. After repairs, go to step 13 . If circuit is okay, go to step 9 .
Check relay control circuit for short to ground. Repair as necessary. After repairs, go to step 13 . If circuit is okay, go to step 9 .
Check for poor connections at relay. Repair as necessary. After repairs, go to step 13 . If connections are okay, go to step 11 .
Check for poor connections at PCM. Repair as necessary. After repairs, go to step 13 . If connections are okay, go to step 12 .
Repair relay feed circuit. After repairs, go to step 13 .
Replace A/C relay. After replacing relay, go to step 13 .
Replace PCM. Program replacement PCM using required equipment. After replacing PCM, go to next step.
Using scan tool, clear DTCs. Operate vehicle within conditions for setting this DTC. If DTC resets, repeat step 2 . If DTC does not reset, system is okay.

An intermittent problem can be caused by a poor connection, rubbed-through wire insulation or broken wire inside insulation. Reviewing FREEZE FRAME/FAILURE RECORDS vehicle mileage since diagnostic test last failed. This may help determine how often condition that caused DTC to be set occurs.

DTC P1546: A/C CLUTCH STATUS CIRCUIT VOLTAGE LOW (5.7L "F" & "Y" BODIES)

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

DTC will also set when PCM has commanded A/C ON and no voltage is detected on A/C clutch status line for greater 5 seconds.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(ref-132811-S27457185922002013000000) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Start and operate engine at idle with A/C on for 5 minutes. If A/C clutch operates properly, go to next step. If A/C clutch does not operate, go to step 5 .
Using scan tool, select ENGINE 1 DATA LIST and monitor A/C status display. If scan tool indicates A/C status as ON, go to next step. If scan tool does not indicate that A/C status as ON, go to step 8 .
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 this DTC. 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»(/gmc/savana/i-1996-2002/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p1537-u1193) .
Turn ignition off. Remove A/C clutch relay. Turn ignition on, with engine off. Using a test light connected to ground, probe ignition feed circuit at A/C relay terminal connector. If test light illuminates, go to next step. If test light does not illuminate, go to step 9 .
Connect a fused jumper wire between ignition feed circuit and A/C clutch status circuit on A/C clutch relay harness. If A/C clutch engages, go to next step. If A/C clutch does not engage, go to step 10 .
Repair A/C clutch relay connection or replace faulty A/C clutch relay. After repairs, go to step 12 .
Repair open in A/C clutch status circuit from splice to PCM. After repairs, go to step 12 .
Repair open in ignition feed circuit to A/C relay. After repairs, go to step 12 .
Repair open in A/C status circuit from A/C relay to splice. After repairs, go to step 12 .
Replace PCM. Program replacement PCM using required equipment. After repair is completed, go to next step.
Using scan tool, select DTC, CLEAR INFO function. Start and warm engine to normal operating temperature. Select DTC, SPECIFIC, then enter this DTC. 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, repeat step 2 .
Using scan tool, select CAPTURE INFO, REVIEW INFO function. If any undiagnosed DTCs are displayed, go to applicable DTC test.

DTC P1554: CRUISE CONTROL STATUS CIRCUIT (3.1L "N" & "W" BODIES & 3.4L "N" BODY & "U" SERIES)

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

Stepper Motor Cruise Control (SMCC) module sends cruise status input to Powertrain Control Module (PCM) to indicate when cruise control is engaged. PCM monitors cruise status signal while commanding cruise control to be disengaged by grounding cruise inhibit circuit.

Following will cause PCM to inhibit cruise control operation

Engine not running long enough for cruise control operation.
Transaxle range inputs indicate Park, Neutral, Low or Reverse gear selected.
Engine or vehicle speed too high or too low.
ABS system is active for longer than 2 seconds.
Vehicle acceleration or deceleration rate is too high.

DTC will set when PCM is commanding the SMCC module to inhibit cruise control operation, cruise status input to PCM indicates that cruise is still active and conditions are present longer than one second.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(ref-132811-S27457185922002013000000) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Check if DTC P1662 is also set. If DTC P1662 is set, diagnose DTC first. If DTC P1662 is not set, go to next step.
Turn ignition off. Disconnect cruise control module. Turn ignition on. Using a DVOM, check cruise control status circuit at cruise control module harness connector and ground. If voltage reading is greater than 7 volts, go to next step. If voltage reading is not greater than 7 volts, go to step 5 .
Turn ignition off. Reconnect cruise control module harness connector. Disconnect PCM harness connector. Turn ignition on. Using a test light connected to battery voltage, probe cruise engaged status circuit at PCM harness connector. If test light illuminates, go to step 6 . If test light does not illuminate, go to step 7 .
Turn ignition off. Disconnect PCM harness connector. Using a test light connected to battery voltage, probe cruise engaged status circuit at PCM harness connector. If test light illuminates, go to step 8 . If test light does not illuminate, go to step 7 .
Replace cruise control module. After replacing cruise control module, go to step 9 .
Replace PCM. Program replacement PCM using required equipment. After replacing PCM, go to step 9 .
Locate and repair short to ground in cruise control status circuit. After repairs, go to next step.
Clear DTC P1554. Start engine and observe DTCs. If DTC P1554 resets, repeat step 2 . If DTC P1554 is not set, repair is complete.

Disconnect and inspect PCM connector. Inspect for damaged pins, corrosion and loose wires. 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 P1554: CRUISE ENGAGED CIRCUIT HIGH VOLTAGE (3.5L "W" BODY)

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

PCM has the ability to disable cruise control if conditions are detected which would make cruise control operation undesirable. The following will cause PCM to inhibit cruise control operation: engine not running long enough for cruise control operation, transaxle range inputs indicate Park, Neutral, Low or Reverse gear selected, engine or vehicle speed too high or too low, ABS system is active for longer than 2 seconds and vehicle acceleration or deceleration rate is too high.

DTC will set when PCM is commanding the cruise control module to inhibit cruise control operation, cruise status input to PCM indicates that cruise is still active and all these conditions are present for longer than one second.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(ref-132811-S27457185922002013000000) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Check if DTC P1585 is also set. If DTC P1585 is set, diagnose DTC P1585 first. If DTC P1585 is not set, go to next step.
Turn ignition off. Disconnect cruise control module. Turn ignition on. Using a DVOM, check cruise control engaged circuit at cruise control module harness connector and ground. If DVOM reads 12 volts, go to next step. If DVOM does not read 12 volts, go to step 5 .
Turn ignition off. Reconnect cruise control module harness connector. Disconnect PCM harness connector. Turn ignition on. Using a test light connected to battery voltage, probe cruise engaged status circuit at PCM harness connector. If test light illuminates, go to step 6 . If test light does not illuminate, go to step 7 .
Check cruise engaged circuit for open or short ground. Repair as necessary. After repairs, go to step 8 . If circuit is okay, go to step 7 .
Replace cruise control module. After replacing cruise control module, go to step 9 .
Replace PCM. Program replacement PCM using required equipment. After replacing PCM, go to step 9 .
Locate and repair short to ground in cruise engaged circuit. After repairs, go to next step.
Clear DTC P1554. Start engine and observe DTCs. If DTC P1554 resets, repeat step 2 . If DTC P1554 is not set, system is okay.

DTC P1554: CRUISE CONTROL STATUS CIRCUIT (3.8L "C", "G", "H" & "W" BODIES)

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

PCM can disable Cruise Control (C/C) if conditions are detected which make C/C operation undesirable. If C/C status signal indicates C/C is engaged when PCM is inhibiting C/C operation, DTC will set.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(ref-132811-S27457185922002013000000) 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 DTCs. If DTC P1676 is set, diagnose DTC P1676 first. If DTC P1676 is not set, go to next step.
Turn ignition off. Disconnect cruise control module connector. Turn ignition on. Using a DVOM, check voltage between engine ground and cruise status circuit at cruise control module connector. If voltage reading is greater than 7 volts, go to next step. If voltage reading is not greater than 7 volts, go to step 5 .
Turn ignition off. Reconnect cruise control module connector. Turn ignition on. Using test light connected to battery voltage, probe cruise control engaged status circuit at PCM connector. If test light illuminates, go to step 6 . If test light does not illuminate, go to step 7 .
Turn ignition off. Disconnect PCM harness connector. Connect test light between battery voltage and cruise engaged status circuit at PCM connector. If test light illuminates, go to step 8 . If test light does not illuminate, go to step 7 .
Replace cruise control module. After replacing module, go to step 9 .
Replace PCM. Program replacement PCM using required equipment. After replacing PCM, go to step 9 .
Locate and repair short to ground in cruise engaged status circuit. After repairs, go to next step.
Clear DTCs. Start engine and read DTCs. If DTC P1554 resets, return to step 2 . If DTC does not reset, repair is complete.

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

DTC P1554: CRUISE ENGAGED CIRCUIT HIGH VOLTAGE (4.0L "G" BODY)

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

PCM will not allow cruise control operation under certain conditions, such as when vehicle speed is too low. This is done by the PCM grounding the 12 volt cruise inhibit switch sent by the cruise control module. If PCM is allowing cruise operation and the operator is requesting for cruise control, the cruise control module will send a cruise engaged signal to the PCM.

This test is used to compare the cruise inhibit output versus the cruise engaged input. DTC will set when the PCM sees that the cruise control module is signaling that it is engaged by sending 12 volts to the cruise engaged circuit while the PCM is inhibiting cruise operation on the cruise inhibit output circuit.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(ref-132811-S27457185922002013000000) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Using scan tool, check if DTC P0503 is also present. If DTC P0503 is present, diagnose DTC first. If DTC P0503 is not present, go to next step.
Ensure DTC was not set due to icy, slippery or wet road conditions. If DTC was set due to road conditions, go to next step. If DTC was not set due to road conditions, see «DIAGNOSTIC AIDS»(/gmc/savana/i-1996-2002/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p1537-u1193) .
Clear DTCs and explain to customer that DTC was set due to slippery, icy or wet road conditions.

Use of the FAILURE REC. mode on scan tool can help diagnose intermittent problems, by displaying how long ago and the conditions under which the DTC set. Use of CRUISE REQUESTED and CRUISE displays can be monitored at the same time to aid in diagnosis an intermittent fault. Clear DTC and operate vehicle under the conditions in which the DTC set.

DTC P1554: CRUISE ENGAGED CIRCUIT HIGH VOLTAGE (4.6L "E" & "K" BODIES - DEVILLE & ELDORADO)

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

If the PCM is allowing cruise control operation and the operator requests cruise, cruise control module will send a cruise engaged signal to PCM. This diagnostic is used to compare the cruise inhibit output versus the cruise engage input. If PCM detects that the cruise control module is signaling that it is engaged, by grounding the cruise engaged input circuit, while the PCM is inhibiting cruise operation on the cruise inhibit output circuit, DTC will set.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(ref-132811-S27457185922002013000000) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Using scan tool, check if DTC P0503 is also present. If DTC P0503 is present, diagnose affected DTC first. If DTC P0503 is not present, go to next step.
Verify if a wheelspin was caused by icy, wet or slippery road condition, causing this DTC to set. If DTC was set due to these road conditions, go to next step. If these road conditions did not set this DTC, see «DIAGNOSTIC AIDS»(/gmc/savana/i-1996-2002/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p1537-u1193) .
Clear DTC. Explain to vehicle operator cause of problem, causing DTC to set.

Both the cruise engaged and cruise displays can be monitored at the same time to aid in diagnosing an intermittent fault. Clear DTCs and operate vehicle within conditions in which DTC will set. Recheck for DTC(s).

DTC P1554: CRUISE CONTROL FEEDBACK CIRCUIT (4.6L "K" BODY - SEVILLE)

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»(ref-132811-S27457185922002013000000) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Using scan tool, check if DTC P1654 is also present. If DTC P1654 is present, diagnose DTC first. If DTC P1654 is not present, go to next step.
Turn ignition on. Using scan tool, select DTC INFO. If scan tool indicates that this DTC failed this ignition, go to next step. If scan tool does not indicate that this DTC failed this ignition, see «DIAGNOSTIC AIDS»(/gmc/savana/i-1996-2002/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p1537-u1193) .
Turn ignition switch to LOCK position. Disconnect cruise control module harness connector. Turn ignition on. Check scan tool. If scan tool indicates that this DTC failed this ignition, go to step 7 . If scan tool does not indicate that this DTC failed this ignition, go to next step.
Record fluid life index as displayed on scan tool. Turn ignition switch to LOCK position. Wait 30 seconds. Disconnect PCM harness connector. Turn ignition on. Check for short in circuit between ground and cruise control module harness connector terminal "J" (cruise engaged output circuit). If circuit is shorted, go to next step. If circuit is okay, go to step 8 .
Repair short to ground in circuit.
Replace cruise control module.
Replace PCM. Program replacement PCM using required equipment.

DTC P1555: EVO CIRCUIT FAULT (1.9L SATURN - DOHC)

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

The Electronic Variable Orifice (EVO) signal is pulse width modulated to control the power steering pressure/flow from the power steering pump. The PCM controls the ground and source voltage. When vehicle speed is zero, current flow is zero milliamps. When vehicle speed reaches 10 MPH, current starts to flow and steering effort begins to increase.

DTC will set if the PCM desired current does not match feedback current when engine has been running for 2.5 seconds or when EVO is commanded (VSS at greater than 10 MPH). EVO circuit is continuously checked with engine running and EVO commanded.

Install scan tool. Start engine. Using scan tool, command assist to FULL and NO while turning steering wheel. If power assist increases and decreases with commands, problem is intermittent. See «DIAGNOSTIC AIDS»(/gmc/savana/i-1996-2002/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p1537-u1193) . If power assist does not respond as commanded, go to next step.
Monitor EVO feedback voltage as NO assist (maximum duty cycle) is commanded. If malfunction history indicates that feedback failed low (open/short to ground), go to step 4 . If malfunction history indicates that feedback failed high (short to voltage in EVO control signal circuit), go to next step.
Turn ignition off. Disconnect PCM harness connector J1. Check voltage on both EVO solenoid terminals at PCM. If voltage reading is present, repair shorted circuit to EVO solenoid. If voltage reading is not present, replace PCM. Check circuit for evidence of short to battery voltage.
Turn ignition off. Disconnect PCM harness connector J1. Check resistance between ground and EVO solenoid harness connector terminals J1D04 and J1D05. If resistance is less than 2 ohms, repair short to ground in circuit. If resistance is not less than 2 ohms, go to next step.
Check resistance between EVO solenoid harness connector terminals. If resistance is less than 8 ohms, check circuits for being shorted to each other or shorted solenoid. If resistance is not less than 8 ohms, go to next step.
If resistance is greater than 12 ohms, check for open in EVO solenoid circuit in fuse block, open EVO solenoid circuit between PCM and solenoid, terminal tightness or open EVO solenoid. If resistance is less than 12 ohms, check for terminal tightness or faulty PCM.

If PCM is defective, verify that EVO solenoid diagnostic feedback circuit is not shorted to battery voltage. A short to voltage in this circuit will damage the internal resistor in the new PCM.

DTC may be set by loss of ignition when vehicle is still moving. This is a normal condition. Review malfunction history data to verify if failure was feedback low/high. Feedback high indicates a short to voltage in EVO control signal circuit. Feedback low indicates an open/short to ground in the circuit.

If DTC is not present but there is a steering effort complaint, diagnose steering system. If EVO solenoid is shorted or if the EVO solenoid circuits are shorted to each other, PCM will not provide output voltage on the EVO control signal circuit. Ignition must be cycled after a repair or DTC P1555 will reset.

DTC P1560: CRUISE CONTROL-TRANSAXLE NOT IN DRIVE (4.0L "G" BODY)

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

If the PCM is allowing cruise control operation and the operator requests cruise, cruise control module will send a cruise engaged signal to PCM. This test will set DTC if cruise control is engaged and transaxle pressure switch in indicating that transaxle is in Park or Neutral. Cruise will disengage when transaxle is shifted out of a drive gear while cruise control is engaged.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(ref-132811-S27457185922002013000000) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Using scan tool, check if DTC P1520, P1554 or P1810 is also present. If any of the DTCs are present, diagnose affected DTC(s) first. If DTCs are not present, go to next step.
Verify if transaxle was shifted into Park or Neutral while cruise control was engaged. If transaxle was shifted out of a drive gear, causing DTC to set, go to next step. If transaxle was not shifted out of a drive gear, see «DIAGNOSTIC AIDS»(/gmc/savana/i-1996-2002/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p1537-u1193) .
Clear DTC. Explain to vehicle operator that shifting transaxle out of a drive gear while cruise control is engaged will set DTC.

Shifting into Neutral while cruise control is engaged will set this DTC. If this DTC was not induced by vehicle operator, use FAILURE REC on scan tool to compare both the TRANS RANGE and PNP displays to verify that operator did not induce DTC. Also, compare both displays to see if transaxle pressure switch circuit may have an intermittent fault. Clear DTC and operate vehicle under the conditions in which the DTC set.

DTC P1560: TRANSAXLE NOT IN DRIVE-CRUISE CONTROL DISABLED (4.6L "K" BODY - SEVILLE)

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

If PCM is allowing cruise control operation and the operator requests cruise, cruise control module will send a cruise engaged signal to PCM. This DTC will set if cruise control is engaged and transaxle pressure switch in indicating that transaxle is in Park or Neutral. Cruise will disengage when transaxle is shifted out of a drive gear while cruise control is engaged.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(ref-132811-S27457185922002013000000) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Using scan tool, check if DTC P1520, P1554 or P1810 is also present. If any of the DTCs are present, diagnose affected DTC(s) first. If DTCs are not present, go to next step.
Verify if transaxle was shifted into Park or Neutral while cruise control was engaged. If transaxle was shifted out of a drive gear, causing DTC to set, go to next step. If transaxle was not shifted out of a drive gear, see «DIAGNOSTIC AIDS»(/gmc/savana/i-1996-2002/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p1537-u1193) .
Clear DTC. Explain to vehicle operator that shifting transaxle out of a drive gear while cruise control is engaged will set DTC.

A complete loss of battery voltage at ECM will cause a no-start condition with no MIL. However, an intermittent loss of battery voltage can also set this DTC. If ECM has been disconnected, or battery power was interrupted during service procedure, this DTC will set.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(ref-132811-S27457185922002013000000) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
If engine starts and runs, fault is not present. See «DIAGNOSTIC AIDS»(/gmc/savana/i-1996-2002/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p1537-u1193) . If engine does not start and run, see appropriate BASIC DIAGNOSTIC PROCEDURES article.

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.

DTC P1564: VEHICLE ACCELERATION TOO HIGH-CRUISE CONTROL DISABLED (4.0L "G" BODY & 4.6L "E" & "K" BODIES)

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

DTC will set when vehicle speed is increasing at an extremely rapid rate (wheelspin). Cruise control is disabled when vehicle suddenly accelerates, such as when traveling on icy roads. DTC being set under this condition is considered normal. Clear DTC and road test vehicle to verify normal operation.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(ref-132811-S27457185922002013000000) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Using scan tool, check if DTC P0503 is also present. If DTC P0503 is present, diagnose affected DTC first. If DTC P0503 is not present, go to next step.
Verify if DTC was set by wheelspin due to icy, wet or slippery conditions. If road conditions caused DTC to set, go to next step. If DTC is not set, fault is not present. See «DIAGNOSTIC AIDS»(/gmc/savana/i-1996-2002/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p1537-u1193) .
Clear DTC. Explain to vehicle operator what caused DTC to set.

Use of the FAILURE REC on scan tool can help diagnose intermittent problems, by displaying how long ago and the conditions under which the DTC set. Clear DTC and operate vehicle under the conditions in which DTC was set.

DTC P1566: ENGINE RPM TOO HIGH-CRUISE CONTROL DISABLED (4.0L "G" BODY & 4.6L "E" & "K" BODIES)

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

DTC will set if engine speed exceeds 5975 RPM while cruise control is engaged. This may occur on slippery pavement, extended wide open throttle acceleration or slipping transaxle. Cruise control disengaging because of these conditions is considered normal. Clear DTC and road test vehicle to verify normal operation.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(ref-132811-S27457185922002013000000) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Verify if DTC was set by wheelspin due to icy, wet or slippery conditions. If road conditions caused DTC to set, go to step 4 . If DTC is not set, go to next step.
Check for mechanical problems, such as transaxle slippage. Repair as necessary. If a mechanical problem is not present, see «DIAGNOSTIC AIDS»(/gmc/savana/i-1996-2002/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p1537-u1193) .
Clear DTC. Explain to vehicle operator what caused DTC to set.

DTC P1567: CRUISE CONTROL DISABLED-ABCS ACTIVE (4.0L "G" BODY & 4.6L "K" BODY - SEVILLE)

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

DTC will set if Active Braking Control System (ABCS) has activated while cruise control was engaged. It is a protective measure to disable the cruise control when ABCS system is engaged.

Perform On-Board Diagnostic (OBD) system check. See ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article.

DTC P1570: TRACTION CONTROL ACTIVE-CRUISE CONTROL DISABLED (4.0L "G" BODY & 4.6L "E" & "K" BODIES)

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

This test indicates that cruise control and traction control are active at the same time. It is a protective measure to disable the cruise control when traveling on icy roads and traction control requesting a maximum torque of less than one percent. Under these conditions DTC P1570 is set and cruise control will be disengaged. Vehicle operator should be advised why cruise control disengaged.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(ref-132811-S27457185922002013000000) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Using scan tool, check if any traction control related DTCs are present. If DTCs are present, diagnose affected DTC(s) first. If other DTCs are not present, go to next step.
Since this DTC was caused most likely by wheel spin due to icy, wet or slippery road conditions, check with vehicle operator when DTC was set. If road condition caused DTC to set, go to next step. If road condition did not cause DTC to set, fault is not present. See «DIAGNOSTIC AIDS»(/gmc/savana/i-1996-2002/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p1537-u1193) .
Explain to vehicle operator the system operation. Clear DTC.

Use of the FAILURE REC. on scan tool can help diagnose intermittent problems, by displaying how long ago and the conditions under which the DTC set. Clear DTC and operate vehicle under the conditions in which it set, if fault condition is suspected.

DTC P1571: TCS DESIRED TORQUE CIRCUIT (3.4L "U" SERIES)

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

Traction Control System (TCS) uses Anti-lock Brake System (ABS) in conjunction with PCM fuel and ignition controls to limit drive wheel slippage during acceleration.

DTC will set when desired torque signal Pulse Width Modulation (PWM) is less than 10 percent or greater than 95 percent and condition is present for at least 10 seconds.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(ref-132811-S27457185922002013000000) 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 traction control desired torque. If desired torque is at or near 100 percent, go to step 4 . If desired torque is not at or near 100 percent, go to next step.
Turn ignition off. Disconnect Electronic Brake and Traction Control Module (EBTCM) connector. Turn ignition on. Using a DVOM, check voltage between engine ground and EBTCM harness connector desired torque PWM circuit. If voltage reading is 5 volts, go to next step. If voltage reading is not 5 volts, go to step 6 .
Turn ignition off. Connect ABS/TCS Pinout Box and Adapter (J39700-25) between EBTCM and EBTCM connector. Using DVOM in Hertz (Hz) scale, check frequency between engine ground and desired torque PWM circuit. Turn ignition on. If frequency is 120-135 Hz, go to next step. If frequency is not 120-135 Hz, go to step 7 .
Using DVOM in duty cycle scale, check duty cycle between engine ground and desired torque PWM circuit. Turn ignition on, with engine off. If duty cycle is 10-95 percent, go to step 9 . If duty cycle is not 10-95 percent, go to step 7 .
Turn ignition off. Disconnect PCM harness connector. Turn ignition on. Check desired torque PWM circuit for open, short to ground or short to voltage. Repair as necessary. After repairs, go to step 11 . If circuit is okay, go to step 9 .
Check for poor connection at EBTCM. Repair as necessary. After repairs, go to step 11 . If connection is okay, go to next step.
Replace EBTCM. After replacing EBTCM, go to step 11 .
Check for poor connection at PCM. Repair as necessary. After repairs, go to step 11 .
Replace PCM. Program replacement PCM using required equipment. After replacing PCM, go to next step.
Clear DTCs. Turn ignition on and observe DESIRED TORQUE PWM scan tool display. If scan tool displays about 100, repair is complete. If scan tool does not display about 100 percent, return to step 2 .

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

DTC P1571: TCS DESIRED TORQUE CIRCUIT (3.5L "W" BODY)

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

This test checks for a Traction Control System (TCS) desired torque signal failure to the PCM. PCM sends 5 volts on the desired torque circuit to the Electronic Brake and Traction Control Module (EBTCM). EBTCM then rapidly switches this circuit to ground creating a Pulse Width Modulated (PWM) frequency signal to request a specific amount of torque reduction during traction control event. DTC will set if this PWM signal is not received by the PCM for 3 seconds.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(ref-132811-S27457185922002013000000) 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, record FAILURE RECORDS and DTC INFO. Clear DTCs. Start and operate engine at idle. Check for stored DTCs. If this DTC failed this ignition cycle, go to next step. If this DTC did not fail in this ignition cycle, fault is not present. See «DIAGNOSTIC AIDS»(/gmc/savana/i-1996-2002/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p1537-u1193) .
Turn ignition off. Disconnect EBTCM harness connector. Start engine. Using a DVOM set to Hertz scale, connect DVOM between engine ground and EBTCM desired torque PWM circuit at harness connector. If DVOM reads 128 Hz, go to next step. If DVOM does not read 128 Hz, go to step 5 .
Check for poor connections or terminal contact at EBTCM. Repair as necessary. After repairs, go to step 8 . If connections or terminal contact are okay, fault is in EBTCM system. Diagnose EBTCM.
Turn ignition off. Disconnect PCM harness connector. Turn ignition on. Check desired torque PWM circuit for open, short to ground or short to voltage. Repair as necessary. After repairs, go to step 8 . If circuit is okay, go to next step.
Check for poor connection at EBTCM. Repair as necessary. After repairs, go to step 8 . If connection is okay, go to next step.
Replace PCM. Program replacement PCM using required equipment. After replacing PCM, go to next step.
Using scan tool, clear DTCs. Turn ignition on. Wait 15 seconds then 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, return to step 2 .
Using scan tool, select CAPTURED INFO feature. If any undiagnosed DTCs are displayed, go to applicable DTC test.

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

DTC P1571: TCS DESIRED TORQUE CIRCUIT (3.8L "C", "G", "H" & "W" BODIES)

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

Traction Control System (TCS) uses Anti-lock Brake System (ABS) in conjunction with PCM fuel and ignition controls to limit drive wheel slippage during acceleration.

DTC will set when desired torque signal Pulse Width Modulation (PWM) is less than 5 percent or greater than 95 percent.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(ref-132811-S27457185922002013000000) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Turn ignition on. Using scan tool, read DESIRED TORQUE. If PWM is about 100 percent, go to step 4 . If PWM is not as specified, go to next step.
Turn ignition off. Disconnect Electronic Brake and Traction Control Module (EBTCM) connector. Turn ignition on. Using a DVOM, check voltage between engine ground and EBTCM harness connector desired torque PWM circuit. If voltage reading is 5 volts, go to next step. If voltage reading is not 5 volts, go to step 6 .
Turn ignition off. Connect ABS/TCS Pinout Box and Adapter (J-39700-25) between EBTCM and EBTCM connector. Using DVOM in Hertz (Hz) scale, check frequency between engine ground and desired torque PWM circuit. Turn ignition on. If frequency is 120-135 Hz, go to next step. If frequency is not as specified, go to step 7 .
Using DVOM in duty cycle scale, check duty cycle between engine ground and desired torque PWM circuit. Turn ignition on, engine off. If duty cycle is 5-95 percent, go to step 9 . If measured duty cycle is not as specified, go to step 7 .
Turn ignition off. Disconnect harness PCM. Turn ignition on. Check desired torque PWM circuit for open, short to ground or short to voltage. Repair as necessary. After repairs are complete, go to step 11 . If circuit is okay, go to step 9 .
Check for faulty connection at EBTCM. Repair as necessary. After repairs, go to step 11 . If connection is okay, go to next step.
Replace EBTCM. After replacing EBTCM, go to step 11 .
Check for faulty connection at PCM. Repair as necessary. After repairs, go to step 11 . If connection is okay, go to next step.
Replace PCM. Program replacement PCM using required equipment. After replacing PCM, go to next step.
Clear DTCs. Turn ignition on and observe DESIRED TORQUE PWM scan tool display. If scan tool displays about 100, repair is complete. If scan tool does not display about 100 percent, return to step 2 .

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

DTC P1571: TCS DESIRED TORQUE CIRCUIT (3.8L "F" BODY)

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

PCM supplies 5 volts on Desired Torque (DT) circuit to Electronic Brake And Traction Control Module (EBTCM). EBTCM toggles this 5-volt signal to ground in order to produce a duty cycle signal. Signal is proportional to the amount of engine output torque requested by EBTCM. EBTCM supplies this signal when it detects a wheel slip.

In order to reduce engine output torque, the PCM reduces the amount of spark advance and in some cases, disables a number of fuel injectors. This diagnostic test check for DT signal failure. DTC will set when PCM does not receive the desired torque signal for 3 seconds.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(ref-132811-S27457185922002013000000) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Turn ignition off. Disconnect EBTCM harness connector. Turn ignition on. Using a DVOM, check voltage between ground and DT circuit at EBTCM connector. If voltage reading is about 5 volts, go to next step. If voltage reading is not about 5 volts, go to step 4 .
Turn ignition on, with engine off. Using scan tool, read DTCs. If any ABS system DTCs are set, diagnose affected ABS DTCs first. If no ABS system DTCs are set, see «DIAGNOSTIC AIDS»(/gmc/savana/i-1996-2002/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p1537-u1193) .
Using a DVOM, check voltage between ground and DT circuit at EBTCM connector. If battery voltage is present, go to step 7 . If battery voltage is not present, go to next step.
Using a test light connected to battery voltage, probe DT circuit at EBTCM connector. If test light illuminates, go to step 8 . If test light does not illuminate, go to next step.
Check for open in DT circuit. Repair as necessary. After repairs, go to step 11 . If circuit is okay, go to step 9 .
Repair short to battery voltage on DT circuit. After repairs, go to step 11 .
Repair short to ground on DT circuit. After repairs, go to step 11 .
Check terminal connections at PCM. Repair terminals as necessary. After repairs, go to step 11 . If terminals are okay, go to next step.
Replace PCM. Program replacement PCM using required equipment. After replacing PCM, go to next step.
Using scan tool, select DTC, CLEAR INFO function. Start and warm engine to normal operating temperature. Select DTC, SPECIFIC, then enter this DTC. 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, repeat step 2 .
Using scan tool, select CAPTURE INFO, REVIEW INFO function. If any undiagnosed DTCs are displayed, go to applicable DTC test.

An intermittent problem can be caused by misrouted harness, rubbed-through wire insulation or broken wire inside insulation.

DTC P1571: TCS PULSE WIDTH MODULATED (PWM) CIRCUIT NO FREQUENCY (4.0L "G" BODY)

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

This test checks for Traction Control System (TCS) PWM signal failure to PCM. The PCM sends 12 volts on the desired torque circuit to the Electronic Brake and Traction Control Module (EBTCM). The EBTCM then rapidly switches this circuit to ground creating a PWM (frequency) signal to request a specific amount of torque reduction during a traction control maneuver. If this PWM signal is not received by the PCM for 3 seconds, DTC will set.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(ref-132811-S27457185922002013000000) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Using scan tool, check for ABS/TCS related DTC(s). If DTCs are present, diagnose affected DTC(s) first. If other DTCs are not present, go to next step.
Check for intermittent terminal connection, intermittent open or short to the desired torque PWM input circuit between PCM connector C2 and EBTCM harness connector terminals. Repair as necessary. If circuit or terminal is okay, fault is not present. See «DIAGNOSTIC AIDS»(/gmc/savana/i-1996-2002/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p1537-u1193) .

If no fault is present, diagnose ABS/TCS system. See appropriate ANTI-LOCK article in BRAKES.

DTC P1571: TCS TORQUE REQUEST CIRCUIT (4.6L "E" & "K" 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»(ref-132811-S27457185922002013000000) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Using scan tool, record any failure records and DTC information. Clear DTCs. Start and operate engine at idle for several minutes. Check for stored DTCs again. If DTC P1571 failed this ignition cycle, go to next step. If DTC P1571 did not fail in this ignition cycle, fault is not present. See «DIAGNOSTIC AIDS»(/gmc/savana/i-1996-2002/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p1537-u1193) .
Turn ignition off. Disconnect EBTCM harness connector. Turn ignition on, engine off. Using DVOM, check voltage between ground and desired torque circuit at EBTCM connector terminal. If voltage reading is 4.8-5.4 volts, go to next step. If voltage reading is not 4.8-5.4 volts, go to step 6 .
Ensure EBTCM connector is still disconnected. Start and operate engine at idle. Using scan tool, monitor the desired torque output. Momentarily short the desired torque circuit to ground at EBTCM connector terminal. If scan tool display reading drops to near zero torque when circuit is grounded, fault is in EBTCM system. Diagnose EBTCM system. See appropriate ANTI-LOCK article in BRAKES. If scan tool reading does not drop, go to next step.
Turn ignition off. Disconnect both PCM harness connectors. Check for short between desired torque circuit and all other 5-volt reference PCM circuits (i.e. TP sensor, EGR position sensor, MAP sensor). Repair as necessary. If circuits are okay, go to step 9 .
If voltage reading is greater than 5.4 volts, go to step 8 . If voltage reading is not greater than 5.4 volts, go to next step.
Turn ignition off. Disconnect both PCM harness connectors. Check for short to ground, open or short to another circuit on desired torque circuit. Repair as necessary. If circuit is okay, go to step 9 .
Check for short to voltage on desired torque output circuit. Repair as necessary. If circuit is okay, go to next step.
Check PCM terminals. Repair as necessary. If terminals are okay, go to next step.
Replace PCM. Program replacement PCM using required equipment.

DTC may set along with others if ignition key is held in CRANK position while engine is running. Starter lock-out function of PCM is enabled several seconds after engine is running, preventing starter from engaging. With key in CRANK position will also cause partial loss of power to some components and systems.

If no fault is present, diagnose ABS/TCS system. See appropriate ANTI-LOCK article in BRAKES.

DTC P1571: ASR DESIRED TORQUE CIRCUIT (5.7L "Y" BODY)

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

PCM supplies 5 volts on Desired Torque (DT) circuit to Electronic Brake And Traction Control Module (EBTCM). EBTCM grounds circuit when it detects wheel slip. DTC sets if DT signal is not received by PCM.

DTC will also set when the desired torque signal is not received by PCM for 3 seconds.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(ref-132811-S27457185922002013000000) 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 DTCs. If any ABS/Traction control DTCs are also set, diagnose affected DTCs first. If no ABS/Traction control DTCs are set, go to next step.
Turn ignition off. Disconnect EBTCM connector. Turn ignition on. Using a DVOM and Connector Test Kit Adaptor (J-35616-A), check voltage between ground and EBTCM connector, DT circuit. If voltage reading is about 5 volts, see appropriate ANTI-LOCK article in BRAKES. If voltage reading is not as specified, go to next step.
Using a DVOM, check voltage between ground and EBTCM connector, DT circuit. If voltage reading is about battery voltage, go to step 7 . If voltage reading is not as specified, go to next step.
Connect a test light between battery positive and EBTCM connector, DT circuit. If test light illuminates, go to step 8 . If test light does not illuminate, go to next step.
Check for open in DT circuit. Repair as necessary. After repairs, go to step 11 . If circuit is okay, go to step 9 .
Repair short to battery voltage on DT circuit. After repairs, go to step 11 .
Repair short to ground on DT circuit. After repairs, go to step 11 .
Check terminal connections at PCM. Repair terminals as necessary. After repairs, go to step 11 . If terminals are okay, go to next step.
Replace PCM. Program replacement PCM using required equipment. After replacing PCM, go to next step.
Using scan tool, select DTC, CLEAR INFO function. Start and warm engine to normal operating temperature. Select DTC, SPECIFIC, then enter this DTC. 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, repeat step 2 .
Using scan tool, select CAPTURE INFO, REVIEW INFO function. If any undiagnosed DTCs are displayed, go to applicable DTC test.

An intermittent problem can be caused by misrouted harness, rubbed-through wire insulation or broken wire inside insulation.

DTC P1573: EBTCM/PCM SERIAL DATA CIRCUIT (3.4L "N" BODY)

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

Powertrain Control Module (PCM) uses serial data line to communicate with various components and systems within vehicle. DTC will set if PCM does not receive data from Electronic Brake and Traction Control Module (EBTCM) or when PCM detects a PCM-to-EBTCM communication error.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(ref-132811-S27457185922002013000000) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Using scan tool, check for PCM DTCs. If any PCM related DTCs are stored, diagnose affected DTCs. If no PCM related DTCs are set, go to next step.
Check for ABS related DTCs. If any ABS related DTCs are stored, diagnose affected DTCs. If no ABS related DTCs are set, go to next step.
Check for poor or intermittent connection at PCM and ABS components. Check for short or open in Class II serial data circuit from PCM to ABS system. Repair as necessary. After repairs, go to step 6. If connections or circuits are okay, go to next step.
Perform ABS diagnostic system check. See appropriate ANTI-LOCK article in BRAKES. Repair as necessary. After repairs, perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(ref-132811-S27457185922002013000000) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. If repairs were not necessary, go to next step.
Read and record FAILURE RECORDS data for this DTC. Clear DTCs. Operate vehicle within conditions noted in FAILURE RECORDS data. Using scan tool, read SPECIFIC DTC. If scan tool displays that this DTC FAILED THIS IGN, return to step 1 . If scan tool does not display that this DTC FAILED THIS IGN, repair is complete.

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

DTC P1573: EBTCM/PCM SERIAL DATA CIRCUIT (3.4L "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»(ref-132811-S27457185922002013000000) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Using scan tool, select ABS DATA. If scan tool displays ABS DATA, go to next step. If scan tool does not display ABS DATA, go to step 4 .
Turn ignition off. Disconnect EBTCM and PCM connectors. Check UART circuit for open between EBTCM and PCM. Repair as necessary. After repairs, go to step 8 . If circuit is okay, go to step 5 .
Turn ignition off, disconnect EBTCM. Turn ignition on. Using a DVOM, check voltage of UART circuit between engine ground and EBTCM harness connector. If voltage constantly varies between zero and 5 volts, go to step 6 . If voltage does not vary as specified, diagnose and repair SDL circuit.
Check UART circuit for faulty connection at PCM. If faulty connection is found, repair as necessary. After repairs, go to step 8 . If connection is okay, see «DIAGNOSTIC AIDS»(/gmc/savana/i-1996-2002/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p1537-u1193) .
Check UART circuit for faulty connection at EBTCM. If faulty connection is found, repair as necessary. After repairs, go to step 8 . If connection is okay, go to next step.
Replace EBTCM. After replacing EBTCM, go to next step.
Read and record FAILURE RECORDS data for DTC P1573. Clear DTCs. Operate vehicle within conditions noted in FAILURE RECORDS data. Using scan tool, read SPECIFIC DTC. If scan tool displays that this DTC FAILED THIS IGN, return to step 2 . If scan tool does not display that this DTC FAILED THIS IGN, repair is complete.

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

DTC P1573: EBTCM/PCM SERIAL DATA CIRCUIT (3.8L "G" 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»(ref-132811-S27457185922002013000000) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Using scan tool, attempt to select ABS data. If ABS data is displayed, go to next step. If ABS data cannot be displayed, go to step 4 .
Turn ignition off. Disconnect PCM and EBTCM. Check for an open in serial data circuit between EBTCM and PCM. Repair as necessary. After repairs, go to step 8 . If circuit is okay, go to step 5 .
Turn ignition off. Disconnect EBTCM. Turn ignition on. Using DVOM, check voltage between ground and serial data circuit terminal at EBTCM harness connector. If voltage constantly varies from 0-5 volts, go to next step. If voltage does not constantly vary from 0-5 volts, check for open or short in serial data circuit. Repair as necessary.
Check serial data circuit for poor terminal connection at PCM. Repair as necessary. After repairs, go to step 8 . If connection is okay, see «DIAGNOSTIC AIDS»(/gmc/savana/i-1996-2002/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p1537-u1193) .
Check serial data circuit for poor terminal connection at EBTCM. Repair as necessary. After repairs, go to step 8 . If connection is okay, go to next step.
Replace EBTCM. After replacing EBTCM, go to next step.
Using scan tool, select CLEAR INFO or CLEAR DTCs function to 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 this DTC until DTC test runs. If scan tool indicates that this DTC FAILED THIS IGN, repeat step 2 . If scan tool does not indicate that this DTC FAILED THIS IGN, repair is complete.

Disconnect and inspect PCM connector. Inspect for damaged pins, corrosion and loose wires. An intermittent problem can be caused by a poor connection, rubbed through wire insulation or broken wire inside insulation. If no problems are found, replace PCM. Reviewing FAILURE RECORDS vehicle mileage since diagnostic test last failed may help determine how often condition that caused DTC to be set occurs.

DTC P1574: STOPLIGHT SWITCH CONTROL CIRCUIT (3.8L "F" BODY)

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

Stoplight switch is normally open. When switch is closed, Throttle Actuator Control (TAC) module senses ignition voltage on brakelight switch signal circuit. DTC will set if TAC module senses voltage on brakelight switch signal circuit when switch should be open.

Condition for setting DTC is when PCM senses this switch is not toggling as compared with other brake switch inputs and condition is present for 20 ACCEL/decel cycles.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(ref-132811-S27457185922002013000000) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Using scan tool, monitor stop/brakelight switch. If scan tool display indicates RELEASED go to next step. If scan tool display does not indicate RELEASED, go to step 7 .
Depress brake pedal about halfway. If scan tool display indicates APPLIED, see «DIAGNOSTIC AIDS»(/gmc/savana/i-1996-2002/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p1537-u1193) . If scan tool display does not indicate APPLIED, go to next step.
Check brakelight switch adjustment. Adjust as necessary. After adjusting switch, go to step 20 . If no adjustment was necessary, go to next step.
Check stop/brakelight fuse. If fuse is blown, go to step 8 . If fuse is okay, go to next step.
Disconnect stop/brakelight switch harness connector. Using a DVOM, check voltage between ground and stop/brakelight feed circuit at harness connector. If battery voltage is present, go to next step. If battery voltage is not present, go to step 12 .
Turn ignition off. Disconnect TAC module and brakelight switch harness connectors. Check continuity of brakelight switch signal circuit. If continuity exists, go to step 10 . If continuity does not exist, go to step 13 .
Disconnect brakelight switch harness connector. Using a test light connected to ground, probe brakelight switch feed circuit at harness connector. If test light illuminates, go to step 14 . If test light does not illuminate, go to next step.
Connect test light to battery voltage and probe brakelight switch signal circuit at harness connector. If test light illuminates, go to step 15 . If test light does not illuminate, go to next step.
Connect test light to ground and probe brakelight switch signal circuit at TAC module harness connector. If test light illuminates, go to step 16 . If test light does not illuminate, go to next step.
Remove brakelight switch. Check continuity across switch terminals while toggling switch by hand. If switch toggles from open to continuity, go to step 18 . If switch does not toggle from open to continuity, go to step 17 .
Repair open in brakelight switch feed circuit. After repairs, go to step 20 .
Repair open in brakelight switch signal circuit. After repairs, go to step 20 .
Repair short to ground in brakelight switch feed circuit. After repairs, go to step 20 .
Repair short to ground in brakelight switch signal circuit. After repairs, go to step 20 .
Repair short to voltage in brakelight switch signal circuit. After repairs, go to step 20 .
Replace stop/brakelight switch. After replacing switch, go to step 20 .
Check for poor connections at brakelight switch and TAC module connectors. Repair as necessary. After repairs, go to step 20 . If connections are okay, go to next step.
Replace TAC module. After replacing module, go to next step.
Using scan tool, select DTC, CLEAR INFO function. Start and warm engine to normal operating temperature. Select DTC, SPECIFIC, then enter this DTC. 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, repeat step 2 .
Using scan tool, select CAPTURE INFO, REVIEW INFO function. If any undiagnosed DTCs are displayed, go to applicable DTC test.

Check brakelight switch adjustment. An intermittent problem can be caused by misrouted harness, rubbed-through wire insulation or broken wire inside insulation.

DTC P1574: STOPLIGHT SWITCH CIRCUIT (4.0L "G" BODY & 4.6L "E" & "K" BODIES)

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

This test functions on the assumption that a sudden decrease in non-drive wheel speed must be caused by a brake application. Non-drive wheel speed and stoplight switch status are supplied to PCM through the serial data from EBTCM. If there is a 2.5 MPH or greater decrease of non-drive wheel speed in.4 second and a transition of the TCC or extended travel contacts of TCC brake switch occurs without a transition of the stoplight switch, DTC will set.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(ref-132811-S27457185922002013000000) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Using scan tool, check of DTC P1602 is also present. If DTC P1602 is present, diagnose this DTC first. If DTC P1602 is not present, see «DIAGNOSTIC AIDS»(/gmc/savana/i-1996-2002/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p1537-u1193) .

DTC P1574 indicates that stoplight switch signal to EBTCM or EBTCM's ability to send stoplight switch signal to PCM has failed. For further diagnosis, see appropriate ANTI-LOCK article in BRAKES.

DTC P1574: STOPLIGHT SWITCH CONTROL CIRCUIT (5.7L "Y" BODY)

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

Conditions for setting DTC are: engine speed greater than 700 RPM, wheel speed greater than 30 MPH to activate diagnostic (diagnostic will be disabled if wheel speed is less than 10 MPH), vehicle speed is decreasing at a rate greater than 10.4 MPH during a one second period.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(ref-132811-S27457185922002013000000) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Using scan tool, monitor stop/brakelight switch. If scan tool display indicates RELEASED go to next step. If scan tool display does not indicate RELEASED, go to step 7 .
Depress brake pedal about halfway. If scan tool display indicates APPLIED, see «DIAGNOSTIC AIDS»(/gmc/savana/i-1996-2002/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p1537-u1193) . If scan tool display does not indicate APPLIED, go to next step.
Check stop/brakelight fuse. If fuse is blown, go to step 11 . If fuse is okay, go to next step.
Disconnect stop/brakelight switch harness connector. Using a test light connected to ground, probe stop/brakelight feed circuit at harness connector. If test light illuminates, go to next step. If test light does not illuminate, go to step 12 .
Jumper stop/brakelight circuit together at harness connector. Observe scan tool. If scan tool display indicates APPLIED, go to step 8 . If scan tool display does not indicate APPLIED, go to step 10 .
Disconnect stop/brakelight switch harness connector. Observe scan tool. If scan tool display indicates RELEASED, go to next step. If scan tool display does not indicate RELEASED, go to step 9 .
Check stop/brakelight switch adjustment. Adjust if necessary. After adjusting stop/brakelight switch, go to step 15 . If stop/brakelight switch does not need adjustment, go to step 13 .
Turn ignition off. Disconnect TAC module harness connector containing stop/brakelight circuit. Check for short in battery feed circuit to stop/brakelight circuit between switch and TAC module. Repair as necessary. After repairs, go to step 15 . If circuit is okay, go to step 14 .
Turn ignition off. Disconnect TAC module harness connector containing stop/brakelight circuit. Check for open in circuit between stop/brakelight switch and TAC module. Repair as necessary. After repairs, go to step 15 . If circuit is okay, go to step 14 .
Repair short to ground in stop/brakelight switch signal circuit. After repairs, go to step 15 .
Repair open between stop/brakelight fuse and switch. After repairs, go to step 15 .
Replace stop/brakelight switch. After replacing switch, go to step 15 .
Replace TAC module. After replacing module, go to next step.
Using scan tool, select DTC, CLEAR INFO function. Start and warm engine to normal operating temperature. Select DTC, SPECIFIC, then enter this DTC. 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, repeat step 2 .
Using scan tool, select CAPTURE INFO, REVIEW INFO function. If any undiagnosed DTCs are displayed, go to applicable DTC test.

Check brakelight switch adjustment. An intermittent problem can be caused by misrouted harness, rubbed-through wire insulation or broken wire inside insulation.

DTC P1575: EXTENDED TRAVEL BRAKE SWITCH CIRCUIT HIGH (4.0L "G" BODY)

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

This test functions on the assumption that a sudden decrease in non-drive wheel speed must be caused by a brake application. Non-drive wheel speed and stop light switch status are supplied to the PCM through the serial data from the EBTCM. If there is a 2.5 MPH or greater decrease of non-drive wheel speed in.2 second and a transition of the TCC or extended travel contacts of the TCC brake switch occurs without a transition of the stop light switch, DTC will set.

Perform On-Board Diagnostic (OBD) system check. See ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, diagnose Traction Control System (TCS). See appropriate ANTI-LOCK article in BRAKES.

The operating conditions as well as the state of the extended travel brake switch circuit will be stored when the DTC was set.

Reviewing the Failure Record may help diagnose an intermittent failure by showing how long ago and under what conditions the DTC set.

DTC P1575: EXTENDED TRAVEL BRAKE SWITCH CIRCUIT (4.6L "E" & "K" BODIES)

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

This test functions on the assumption that a sudden decrease in non-drive wheel speed must be caused by a brake application. Non-drive wheel speed and stoplight switch status are supplied to PCM through the serial data from EBTCM. If there is a 2.5 MPH or greater decrease of non-drive wheel speed in.2 second and a transition of the TCC or extended travel contacts of the TCC brake switch occurs without a transition of the stoplight switch, DTC will set.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(ref-132811-S27457185922002013000000) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Turn ignition on. Using scan tool in ENGINE 1 mode, note EXT TRAVEL BRAKE display. If scan tool display indicates RELEASED, go to next step. If scan tool display does not indicate RELEASED, go to step 7 .
Depress brake pedal about half way. If scan display indicates APPLIED, fault is not present. See «DIAGNOSTIC AIDS»(/gmc/savana/i-1996-2002/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p1537-u1193) . If scan tool display does not indicate APPLIED, go to next step.
Disconnect extended travel brake switch connector. If scan tool display indicates APPLIED, go to step 21 . If scan tool display does not indicate APPLIED, go to next step.
Store fluid life index as indicated on scan tool. Turn ignition off and wait 30 seconds, then disconnect PCM harness connector C1. Turn ignition on. Using DVOM, check voltage between ground and TCC brake switch input circuit terminal at PCM harness connector C1. If voltage reading is greater than.5 volt, go to next step. If voltage reading is not greater than.5 volt, go to step 19 .
Repair short to voltage between extended travel brake switch input circuit.
Note TCC BRAKE SWITCH display on scan tool. If scan tool display indicates RELEASED, go to next step. If scan tool display does not indicate RELEASED, go to step 11 .
Disconnect extended travel brake switch harness connector. Using DVOM, check voltage between ground and extended travel brake switch terminal "C". If voltage reading is 10 volts or greater, go to next step. If voltage reading is not 10 volts or greater, go to step 17 .
Using jumper wire, jumper extended travel brake switch terminals "C" and "D". If scan tool display indicates RELEASED, go to step 21 . If scan tool display does not indicate RELEASED, go to next step.
Store fluid index as indicated on scan tool. Turn ignition off and wait 30 seconds, then disconnect PCM harness connector C1. Turn ignition on. Using DVOM, check voltage between ground and TCC brake switch input circuit at PCM harness connector C1 terminal. If voltage reading is 10 volts or greater, go to step 13 . If voltage reading is not 10 volts or greater, go to step 18 .
Check fuse to shift solenoid. If fuse is faulty, go to step 13 . If fuse is okay, go to next step.
Disconnect extended travel brake switch connector. Using DVOM, check voltage between ground and extended travel brake switch connector terminal "C". If voltage reading is 10 volts or greater, go to step 21 . If voltage reading is not 10 volts or greater, go to step 16 .
Store fluid life index as indicated on scan tool. Turn ignition off and wait 30 seconds, then disconnect PCM harness connector C1. Using DVOM, individually check the resistance to all the extended travel switch connector terminals. If resistance is less than 100 ohms on any of the terminals, go to next step. If resistance is not less than 100 ohms on any of the terminals, go to step 15 .
Repair short in the circuits with low resistance. Replace fuse.
Check for intermittent short to ground on both extended travel and TCC brake switch circuits. Repair as necessary. Replace fuse.
Repair open in circuit to EBTCM.
Repair open in circuit to shift solenoid fuse.
Repair open in circuit between switch and EBTCM.
Check terminal contact at PCM harness connector C1. Repair as necessary. If terminal contact is okay, go to next step.
Replace PCM. Program replacement PCM using required equipment.
Check for proper adjustment of extended travel brake switch. Adjust as necessary. If adjustment was not necessary, go to next step.
Replace extended travel brake switch.

Use FAILURE REC. information on scan tool to help diagnose an intermittent problem. The operating conditions as well as the state of the extended travel brake switch circuit will be stored when DTC was set.

DTC P1575: EXTENDED TRAVEL BRAKE SWITCH CIRCUIT HIGH (5.7L "Y" BODY)

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

Extended Travel Brake (ETB) switch is normally closed. When switch is closed, PCM senses ignition voltage on ETB switch signal circuit. This DTC sets if PCM senses voltage on ETB switch signal circuit when switch should be open.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(ref-132811-S27457185922002013000000) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Start engine. Using scan tool, monitor ETB switch. If scan tool displays RELEASED, go to next step. If scan tool does not display RELEASED, go to step 7 .
Start engine. Using scan tool, monitor ETB switch. Depress brake pedal about halfway down. If scan tool displays APPLIED, see «DIAGNOSTIC AIDS»(/gmc/savana/i-1996-2002/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p1537-u1193) . If scan tool does not display APPLIED, go to next step.
Check ETB switch adjustment. Adjust if necessary. After adjustment, go to step 17 . If adjustment is not necessary, go to next step.
Turn engine off. Disconnect ETB switch connector. Turn ignition on, with engine off. If scan tool displays APPLIED, go to step 14 . If scan tool does not display APPLIED, go to next step.
Turn ignition off. Disconnect PCM harness connector. Turn ignition on, with engine off. Using a DVOM, check voltage on ETB switch signal circuit. If voltage reading is greater than.5 volt, go to next step. If voltage reading is not greater than.5 volt, go to step 16 .
Turn ignition off. Disconnect ETB switch harness connector. Turn ignition on, with engine off. Using a test light connected to ground, probe ignition feed circuit at ETB switch harness connector. If test light illuminates, go to next step. If test light does not illuminate, go to step 11 .
Turn ignition off. Jumper ETB signal circuit to ignition feed circuit at harness connector. Turn ignition on, with engine off. Using scan tool, monitor ETB switch parameter. If scan tool displays RELEASED, go to step 13 . If scan tool does not display RELEASED, go to next step.
Turn ignition off. Disconnect PCM harness connector. Check continuity of ETB switch signal circuit. If continuity exists, go to step 15 . If continuity does not exist, go to step 12 .
Repair short to voltage in ETB switch signal circuit. After repairs, go to step 17 .
Repair open in ETB switch ignition feed circuit. After repairs, go to step 17 .
Repair open in ETB switch signal circuit. After repairs, go to step 17 .
Check for poor connections at ETB switch connector. Repair as necessary. After repairs, go to step 17 . If connections are okay, go to next step.
Replace ETB switch. After replacing switch, go to step 17 .
Check for poor connections at PCM harness connector. Repair as necessary. After repairs, go to step 17 . If connections are okay, go to next step.
Replace PCM. Program replacement PCM using required equipment. After replacing PCM, go to next step.
Using scan tool, select DTC, CLEAR INFO function. Start and warm engine to normal operating temperature. Select DTC, SPECIFIC, then enter this DTC. 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, repeat step 2 .
Using scan tool, select CAPTURE INFO, REVIEW INFO function. If any undiagnosed DTCs are displayed, go to applicable DTC test.

Check ETB switch adjustment. An intermittent problem can be caused by misrouted harness, rubbed-through wire insulation or broken wire inside insulation.

DTC P1579: PARK/NEUTRAL-TO-DRIVE/REVERSE THROTTLE ANGLE-POWER REDUCTION MODE ACTIVE (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 detect if transaxle is placed in gear under conditions that may cause damage to vehicle powertrain or create an unsafe condition. When such condition exists, DTC will set and engine power will be reduced by disabling fuel injector to individual cylinders.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(ref-132811-S27457185922002013000000) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Since this DTC will set when the vehicle is shifted into Drive/Reverse under possibly damaging conditions, check with vehicle operator to verify under which condition the DTC set. If vehicle operator actions caused this DTC to set, fault is not present. See «DIAGNOSTIC AIDS»(/gmc/savana/i-1996-2002/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p1537-u1193) . If vehicle operator did not cause DTC to set, go to next step.
Check for proper adjustment of transaxle range switch and for poor terminal contact at switch and the PCM. Repair as necessary. If adjustment or terminal contact is okay, fault is not present. See «DIAGNOSTIC AIDS»(/gmc/savana/i-1996-2002/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p1537-u1193) .

If driver's action caused the DTC to set, clear DTC and inform driver of proper shift procedure. Use FAILURE REC. information on scan tool to help diagnose an intermittent problem. Manipulate wiring harness while watching scan tool display, looking of an open or short in circuit.

DTC P1580: CRUISE CONTROL MOVE CIRCUIT VOLTAGE LOW (1.9L SATURN)

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

PCM provides about 12 volts (ignition voltage) to control movement of the cruise module motor. The feedback signal internal to the PCM monitors the cruise move diagnostic feedback circuit (circuit No. 1886) and compares low versus high as the Quad Driver Module (QDM) is turned on and off. If voltage levels are too low when the QDM driver is turned on, DTC will set. Conditions for setting DTC are: the cruise move diagnostic feedback circuit (circuit No. 1886) is less than 7 volts when driver is turned on. The cruise move circuit is tested continuously anytime ignition is on.

Install scan tool. Start engine. Check for active DTCs. If DTC P1580 is active, go to next step. If DTC is not active, problem is intermittent. See «DIAGNOSTIC AIDS»(/gmc/savana/i-1996-2002/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p1537-u1193) .
Turn ignition off. Disconnect cruise control module harness connector. Start engine. If DTC is still active, check for short to ground in cruise move diagnostic feedback circuit. If circuit is okay, replace PCM. If DTC is not active, replace cruise control module.

If an intermittent condition exists, check parameter on scan tool while moving connectors and harnesses. Check malfunction history data to determine when the condition existed and attempt to reproduce condition.

DTC P1581: CRUISE CONTROL MOVE CIRCUIT VOLTAGE HIGH (1.9L SATURN)

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

PCM provides about 12 volts (ignition voltage) to control movement of the cruise module motor. The feedback signal internal to the PCM monitors the cruise move diagnostic feedback circuit (circuit No. 1886) and compares low versus high as the Quad Driver Module (QDM) is turned on and off. If voltage levels are too high when the QDM driver is turned off, DTC will set. Conditions for setting DTC are: cruise move diagnostic feedback circuit (circuit No. 1886) is greater than 3 volts when driver is turned off. The cruise move circuit is tested continuously anytime ignition is on.

Install scan tool. Start engine. Check for active DTCs. If DTC P1581 is active, go to next step. If DTC is not active, problem is intermittent. See «DIAGNOSTIC AIDS»(/gmc/savana/i-1996-2002/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p1537-u1193) .
If DTCs P1581 and P1583 are both present, check for open in ground circuit to cruise control module. If only DTC P1581 is present, go to next step.
Turn ignition off. Disconnect cruise control module harness connector. Using a fused (5-amp) jumper wire, jumper cruise move diagnostic feedback signal circuit (circuit No. 1886) to ground. Start engine. If DTC P1581 is still active, check for open in circuit. If circuit is okay, replace PCM. If DTC P1581 is not active, go to next step.
If jumper fuse blew, repair circuit for short to voltage. If jumper fuse did not blow, replace cruise control module.

DTC P1582: CRUISE CONTROL DIRECTION CIRCUIT LOW VOLTAGE (1.9L SATURN)

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

PCM provides about 12 volts (ignition voltage) to cruise module when movement of throttle toward WOT is desired. At rest (QDM off), the circuit is low and motor direction is driven towards idle. The PCM internal diagnostic feedback monitors the cruise direction diagnostic feedback signal circuit (circuit No. 1887) and compares low versus high as the Quad Driver Module (QDM) is turned on and off. If voltage reading is too low when the QDM driver is turned on, DTC will set. Conditions for setting DTC are: the cruise direction diagnostic feedback circuit (circuit No. 1887) is less than 7 volts when driver is turned on. The cruise move circuit is tested continuously anytime ignition is on.

Install scan tool. Start engine. Using scan tool, command cruise control test function and observe cruise control rod. If accelerator moves, problem is intermittent. See «DIAGNOSTIC AIDS»(/gmc/savana/i-1996-2002/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p1537-u1193) . If accelerator does not move, go to next step.
Turn ignition off. Disconnect cruise control module harness connector. Start engine. If DTC P1583 is still active, replace cruise control module. If DTC is not active, check for short to ground in cruise direction diagnostic feedback circuit (circuit No. 1887). If circuit is okay, replace PCM.

DTC P1583: CRUISE CONTROL DIRECTION CIRCUIT HIGH VOLTAGE (1.9L SATURN)

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

PCM provides about 12 volts (ignition voltage) to cruise module when movement of the throttle toward WOT is desired. At rest (QDM off), the circuit is low and motor direction is driven toward idle. The PCM internal diagnostic feedback circuit (circuit No. 1887) monitors and compares low versus high as the Quad Driver Module (QDM) is turned on and off. If voltage is too high when the QDM driver is turned off, DTC will set. Conditions for setting DTC are: the cruise direction diagnostic feedback circuit (circuit No. 1887) is greater than 3 volts when driver is turned off. The cruise direction circuit is tested continuously anytime ignition is on.

Install scan tool. Start engine. Check for active DTCs. If DTC P1583 is active, go to next step. If DTC is not active, problem is intermittent. See «DIAGNOSTIC AIDS»(/gmc/savana/i-1996-2002/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p1537-u1193) .
If DTCs P1581 and P1583 are both present, check for open in ground circuit to cruise control module. If only DTC P1581 is present, go to next step.
Turn ignition off. Disconnect cruise control module harness connector. Using a fused (5-amp) jumper wire, jumper cruise direction diagnostic feedback signal circuit (circuit No. 1887) to ground. Start engine. If DTC P1583 is still active, check for open in circuit. If circuit is okay, replace PCM. If DTC P1583 is not active, go to next step.
If jumper fuse blew, repair circuit for short to voltage. If jumper fuse did not blow, replace cruise control module.

DTC P1584: CRUISE DISENGAGE (1.9L SATURN)

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

DTC will set if the PCM disengages cruise control. Normal vehicle operator induced commands such as brake on/off, cruise switch on/off, etc. will not set DTC. However, it is possible for vehicle operator to induce this DTC with abnormal driving maneuvers such as, shifting from D4 to Neutral or applying emergency brake while cruise is engaged.

PCM will disengage cruise and set DTC if the following conditions are met, ignition voltage is less than 10 volts or greater than 16 volts, vehicle acceleration is greater than 10 MPH per second or when traction control is active, decel is greater than 4 MPH per second, speed error is greater than 15 MPH for 10 seconds or 20 MPH instantaneously (caused if on steep hills), engine speed out of range, gear out of range (invalid gear ratio selection for cruise), or failure in PNP switch (A/T only).

Use of malfunction history records in scan tool parameter will help diagnose drive induced versus system failures. If DTC P1640 or P1641 is present, diagnose this DTC(s) first.

DTC P1585: CRUISE INHIBIT CONTROL CIRCUIT (3.4L "U" SERIES)

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

A history DTC will clear after 40 consecutive warm-up cycles have occurred without a malfunction. DTC will also clear when battery is disconnected or cleared by scan tool.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(ref-132811-S27457185922002013000000) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Turn ignition off. Disconnect PCM harness connector. Turn ignition on. Using a DVOM, check voltage between ground and stepper motor cruise inhibit control circuit at PCM harness connector. If battery voltage is present, go to next step. If battery voltage is not present, go to step 6 .
Connect DVOM between ground and cruise control inhibit control circuit at PCM harness connector. Monitor reading for about 2 minutes. If DVOM reads.001-.500 amp, go to step 11 . If DVOM does not read.001-.500 amp, go to next step.
Turn ignition off. Disconnect stepper motor cruise control module. Ensure PCM harness connector is disconnected. Turn ignition on. Check voltage between ground and cruise inhibit control circuit. If DVOM reads zero volts, go to step 10 . If DVOM does not read zero volts, go to next step.
Locate and repair short to voltage in cruise inhibit control circuit. After repairs, go to step 16 .
Turn ignition off. Check ignition feed fuse for stepper motor cruise control module. If fuse is blown, go to next step. If fuse is not blown, go to step 8 .
Repair short to ground in ignition feed circuit for stepper motor cruise control module. Repair as necessary. Replace fuse. After repairs, go to step 16 .
Disconnect stepper motor cruise control module. Turn ignition on. Check voltage between ground and ignition feed circuit for stepper motor cruise control module. If battery voltage is present, go to next step. If battery voltage is not present, go to step 13 .
Check cruise inhibit control circuit for open or short to ground. Repair as necessary. After repairs, go to step 16 . If circuit is okay, go to next step.
Check cruise inhibit control circuit for poor connection at PCM and at stepper motor cruise control module. Repair as necessary. After repairs, go to step 16 . If connections are okay, go to step 14 .
Turn ignition off. Reconnect PCM harness connector. Disconnect stepper motor cruise control module harness connector. Turn ignition on. Using a test light, connect test light between cruise inhibit control circuit and ignition feed circuit at stepper motor cruise control module harness connector. Using scan tool in OUTPUT TEST function, cycle cruise inhibit output on and off. If test light flashes on and off, see «DIAGNOSTIC AIDS»(/gmc/savana/i-1996-2002/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p1537-u1193) . If test light does not flash on and off, go to next step.
Check cruise control inhibit circuit for poor connection at PCM. Repair as necessary. After repairs, go to step 16 . If connection is okay, go to step 15 .
Locate and repair open in ignition feed circuit to stepper motor cruise control module. After repairs, go to step 16 .
Replace stepper motor cruise control module. After replacing module, go to step 16 .
Replace PCM. Program replacement PCM using required equipment. After replacing PCM, go to next step.
Using scan tool, select DTC, CLEAR INFO function. Start and warm engine to normal operating temperature. Select DTC, SPECIFIC, then enter this DTC. Operate vehicle within 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, repeat step 2 .

DTC P1585: CRUISE INHIBIT CONTROL CIRCUIT (3.5L "W" BODY)

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

The cruise control module pulls the cruise inhibit circuit up to about 12 volts. When PCM determines that cruise control is allowed, PCM grounds the cruise inhibit circuit. The cruise control module detects the low voltage signal and enables the system. The PCM grounds the cruise inhibit circuit through an internal solid state device called a driver. The driver supplies ground to the component being controlled. Each driver has a fault line which is monitored by the PCM. DTC will set if fault detection circuit senses a voltage other than what is expected.

Conditions for setting DTC are: there is a short to ground, open in circuit, or short to battery voltage is detected on control circuit and fault is present for at least 30 seconds.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(ref-132811-S27457185922002013000000) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Turn ignition off. Disconnect PCM harness connector. Turn ignition on. Using a DVOM, check voltage between ground and cruise inhibit control circuit at PCM harness connector. If battery voltage is present, go to next step. If battery voltage is not present, go to step 6 .
Connect DVOM between ground and cruise control inhibit control at PCM harness connector. Monitor reading for about 2 minutes. If DVOM reads.001-.500 amp, go to step 11 . If DVOM does not read.001-.500 amp, go to next step.
Turn ignition off. Disconnect stepper motor cruise control module. Ensure PCM harness connector is disconnected. Turn ignition on. Check voltage between ground and cruise inhibit control circuit. If DVOM reads zero volts, go to step 10 . If DVOM does not read zero volts, go to next step.
Locate and repair short to voltage in cruise inhibit control circuit, go to step 16 .
Check ignition feed fuse for stepper motor cruise control module. If fuse is blown, go to next step. If fuse is not blown, go to step 8 .
Check for short to ground in ignition feed circuit for stepper motor cruise control module. Repair as necessary. Replace fuse. After repairs, go to step 16 . If circuit is okay, go to step 14 .
Disconnect stepper motor cruise control module. Turn ignition on. Check voltage between ground and ignition feed circuit for stepper motor cruise control module. If battery voltage is present, go to next step. If battery voltage is not present, go to step 13 .
Check cruise inhibit control circuit for open or short to ground. Repair as necessary. After repairs, go to step 16 . If circuit is okay, go to next step.
Check cruise inhibit control circuit for poor connection at PCM and at stepper motor cruise control module. Repair as necessary. After repairs, go to step 16 . If connections are okay, go to step 14 .
Turn ignition off. Reconnect PCM harness connector. Disconnect stepper motor cruise control module harness connector. Turn ignition on. Using a test light, connect test light between cruise inhibit control circuit and ignition feed circuit at stepper motor cruise control module harness connector. Using scan tool in OUTPUTS TEST function, cycle cruise inhibit output on and off. If test light flashes on and off, problem is intermittent. If test light does not flash on and off, go to next step.
Check cruise control inhibit circuit for poor connection at PCM. Repair as necessary. After repairs, go to step 16 . If connection is okay, go to step 15 .
Locate and repair open in ignition feed circuit to step per motor cruise control module. After repairs, go to step 16 .
Replace stepper motor cruise control module. After replacing module, go to step 16 .
Replace PCM. Program replacement PCM using required equipment. After replacing PCM, go to next step.
Using scan tool, select DTC, CLEAR INFO function. Start and warm engine to normal operating temperature. Select DTC, SPECIFIC, then enter this DTC. 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, repeat step 2 .
Using scan tool, select CAPTURE INFO function. If any undiagnosed DTCs are displayed, go to applicable DTC test.

PCM has a DTC associated with start/stall to assist in diagnosis of intermittent conditions. This DTC will set if engine is in the run mode and Crankshaft Position (CKP) sensor signal is lost when ignition has not been cycled. This DTC will not turn on the MIL. DTC can be set through driver error, such as, vehicle equipped with manual transmission and clutch is released too quickly, stalling engine, or when engine is run mode, ignition voltage is present but CKP sensor pulses to the PCM are missing.

Check if DTC P0336 is also present. If P0336 is present, perform DTC P0336 diagnostic test.
Verify that driver/vehicle operator error did not induce DTC to set. Using scan tool, view malfunction history and attempt to duplicate condition.

If no other DTCs are present and customer complaint symptoms have been verified, see appropriate TROUBLE SHOOTING - NO CODES article. If other DTCs are present, diagnose affected DTC(s) first.

DTC P1599: ENGINE STALL OR NEAR STALL DETECTED (4.0L "G" BODY & 4.6L "E" & "K" BODIES)

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

This test checks for an engine stall or near stall and sets DTC P1599 if a stall condition is detected. A partial start when engine RPM exceeds 400 RPM and the engine does not start, will also cause DTC to set. This DTC is designed to capture snapshot data of the stall condition and may set as the ignition is turned off, if the injectors or IC module lose power before the PCM.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(ref-132811-S27457185922002013000000) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
If complaint is engine stalling, go to next step. If engine is not stalling, fault is not present. See «DIAGNOSTIC AIDS»(/gmc/savana/i-1996-2002/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p1537-u1193) .
Turn ignition on. Using scan tool, check if other DTCs are present. If other DTCs are present, diagnose affected DTC(s) first. If no other DTCs are present, go to next step.
Select DATA LIST under SPECIFIC ENGINE and select DTC P1599. Note MAP sensor display taken at the time this DTC was set. If scan tool displayed value is greater than 95 kPa, go to next step. If scan tool displayed value is not greater than 95 kPa, see appropriate TROUBLE SHOOTING - NO CODES article.
Stalling can be caused by either fuel system, idle speed control, emissions related components or faulty wiring and connections. Perform fuel system check. See appropriate BASIC DIAGNOSTIC PROCEDURES article. Repair as necessary. If fault is not found or if related systems are okay, go to next step.
Check for TCC that is improperly applied due to grounded TCC solenoid circuit or by transaxle hydraulic problems. For diagnosis of hydraulic problems, see appropriate TRANSMISSION SERVICING article in AUTOMATIC TRANSMISSIONS. Check ignition switch circuits for intermittent open to PCM or IC module. Wiggle ignition key while driving to check for intermittent ignition switch connection or switch out of adjustment. Check PCM and IC module ground. Check for intermittent injector circuit operation. Check fuel pump ground for loose or poor connection. Repair as necessary. If repair was not necessary, see «DIAGNOSTIC AIDS»(/gmc/savana/i-1996-2002/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p1537-u1193) .

Use scan tool snapshot data taken of DTC P1599 to determine cause of stalling condition.

This DTC will set when TC determines there is a fault internally with the serial data link to the PCM.

Check CKP sensor for proper operation. See appropriate SYSTEM & COMPONENT TESTING article. Reprogram PCM and verify if fault or DTC resets. If DTC P1601 resets, replace PCM. Program replacement PCM using required equipment.

Extremely high temperatures can affect ECM, thus reducing reliability. ECM is enclosed within relay center in engine compartment. A small fan, located in left front fender, directs fresh air through relay center to reduce ECM temperature. This fan is not ECM controlled and is designed to operate in conjunction with engine cooling fans. An inoperative fan, or an obstructed airflow may allow ECM to overheat. If ECM detects it is getting too hot, this DTC will set.

Conditions for setting DTC are: ECM temperature is greater than 221°F (105°C), or internal temperature sensor value is less than -58°F (-50°C) or greater than 284°F (140°C).

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(ref-132811-S27457185922002013000000) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Using scan tool, clear DTCs. Turn ignition off for 15 seconds. Allow ECM to cool down. Start engine and operate vehicle. Check for DTCs. If DTC P01601 is set, go to step 4 . If DTC P01601 is not set, go to next step.
Ensure ECM and/or other components are properly mounted in engine compartment relay center. Ensure relay center cover is installed properly and that relay center is not damaged. Check for debris and other obstructions in airflow path. Check for debris in fan and fan air inlet. Repair as necessary. If no problem is found, and fans do not operate, see appropriate SYSTEM & COMPONENT TESTING article to diagnosis electric cooling fans.
Replace ECM. New ECM must be programmed with theft deterrent module frequency code currently on vehicle.

DTC P1602: ABS MESSAGE FAULT (1.9L SATURN)

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

PCM receives messages from the ABS controller to activate the traction control system. When messages are not transmitted properly between the ABS controller and PCM, DTC will set.

Conditions for setting DTC are: no message is received from the ABS controller or a certain number of incorrect messages have been sent to the PCM. ABS controller circuit is continuously checked when ignition is on.

Install scan tool. Check if scan tool can communicate with PCM. If scan tool communication is okay, go to next step. If scan tool does not communicate with PCM, perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(ref-132811-S27457185922002013000000) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article.
Clear DTC. Unplug scan tool. Start and operate engine for about one minute. If DTC P1602 resets, go to next step. If DTC does not reset, problem is intermittent. See «DIAGNOSTIC AIDS»(/gmc/savana/i-1996-2002/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p1537-u1193) .
Turn engine off. Disconnect ABS controller and PCM harness connector J1. Check continuity on circuit between ABS module harness connector terminal and PCM harness connector terminal. If continuity exists, go to next step. If continuity does not exist, check for open in circuit.
Check continuity between PCM terminals No. J1D08 and J1D09. If continuity exists, check for terminal tightness or faulty ABS controller. If continuity does not exist, replace PCM.

Check terminal tightness at PCM and ABS controller connectors. If DTC P1602 is present, traction control will be disabled.

ECM employs an internal circuit to continuously monitor knock control evaluation circuit. Knock Sensor (KS) module circuit contains circuitry that allows ECM to utilize KS signals and diagnose KS sensors and circuitry. KS module is not a replaceable component. If ECM detects a fault in ability of circuit to sample these signals, this DTC will set.

DTC will also set when ECM detects a fault in internal knock sensor control circuit.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(ref-132811-S27457185922002013000000) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Replace ECM. New ECM must be programmed with theft deterrent module frequency code currently on vehicle. After replacing ECM, 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 P1602 is set, go to step 2 . If DTC P1602 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 P1602: EBCM/EBTCM SERIAL DATA CIRCUIT (3.1L "N" & "W" BODIES)

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

A Class II serial data communications system is used on these vehicles to allow various modules to communicate and share information with each other. Each bit of information has 2 lengths, long or short. This allows vehicle wiring to be reduced and the transmission and reception of multiple signals over a single wire. The messages carried on a Class II serial data streams are also prioritized. If two messages attempt to establish communications on the data line at the same time, the message with a higher priority will continue. The message with a lower priority will wait. If a module cannot respond to the PCM, a DTC will set.

DTC will set when ignition is on, system voltage is greater than 8.2 volts and PCM cannot communicate with EBCM.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(ref-132811-S27457185922002013000000) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Check if scan tool can display data from PCM. If data is displayed, go to next step. If data cannot be displayed, diagnose data link connector.
Check an intermittent, short, or open connection on serial data circuit to EBCM. Repair as necessary. After repairs, go to step 6 . If circuit is okay, go to next step.
Check an intermittent, short, or open connection on serial data circuit to BFC. Repair as necessary. After repairs, go to step 6 . If circuit is okay, go to next step.
Check for DTCs or communication with other modules. Repair as necessary. After repairs, go to next step.
Using scan tool, clear DTCs. Start and warm engine to normal operating temperature. Operate vehicle within conditions for setting this DTC. If scan tool indicates that this diagnostic ran and passed, go to next step. If scan tool does not indicate that this diagnostic ran and passed, repeat step 2 .
Check if any additional DTCs are set. Diagnose affected DTCs. If DTCs are not set, system is okay.

Attempting to start vehicle by by-passing the Passlock® system or substituting parts without performing the password learn procedure may set DTC P1610, P1626, P1630 or P1632.

If no password is received, DTC P1610, P1626, P1631 or P1632 may set. An intermittent may be caused by poor connection, rubbed through wire insulation or a wire broken inside the insulation.

DTC P1602: EBCM/EBTCM SERIAL DATA CIRCUIT (3.4L "N" BODY)

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

A Class II serial data communications system is used to allow various modules to communicate and share information with each other. Each bit of information has 2 lengths, long or short. This allows vehicle wiring to be reduced and the transmission and reception of multiple signals over a single wire. The messages carried on a Class II serial data streams are also prioritized. If 2 messages attempt to establish communications on the data line at the same time, the message with a higher priority will continue. The message with a lower priority will wait. If a module cannot respond to the PCM, a DTC will set.

Conditions for setting DTC are: ignition is on and system voltage is greater than 8.2 volts and PCM is detecting a loss of serial data from EBCM for longer than 5 seconds.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(ref-132811-S27457185922002013000000) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Using scan tool, attempt to select ABS data. If ABS data can be displayed, go to next step. If ABS data cannot be displayed, go to step 4 .
Turn ignition off. Disconnect PCM and EBCM/EBTCM harness connectors. Check serial data circuit for open between EBCM/EBTCM and PCM. Repair as necessary. After repairs, go to step 6. If circuit is okay, see «DIAGNOSTIC AIDS»(/gmc/savana/i-1996-2002/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p1537-u1193) .
Check serial data circuit for poor connection at EBCM/EBTCM. Repair as necessary. After repairs, go to step 6 . If connections are okay, go to next step.
Check serial data circuit for poor connection to PCM. Repair as necessary. After repairs, go to next step. If connections are okay, diagnose ABS system. See appropriate ANTI-LOCK article in BRAKES.
Using scan tool, clear DTCs. Start and warm engine to normal operating temperature. Operate vehicle within conditions for setting this DTC. If scan tool indicates that this diagnostic ran and passed, system is okay. If scan tool does not indicate that this diagnostic ran and passed, repeat step 2 .

An intermittent may be caused by a poor connection, rubbed-through wire insulation or a broken wire inside the insulation.

DTC P1602: LOSS OF EBTCM SERIAL DATA (3.5L "W" BODY)

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

This test checks for absent or invalid EBTCM serial data to the PCM. When such conditions exists for 11 seconds, DTC will set.

Perform On-Board Diagnostic (OBD) system check. See ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, diagnose ABS/TCS system. See appropriate ANTI-LOCK article in BRAKES.

DTC P1602: EBCM/EBTCM SERIAL DATA CIRCUIT (3.8L "C" & "W" BODIES)

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

A serial data communications system is used on these vehicles to allow various modules to communicate and share information with each other. Each bit of information has 2 lengths, long or short. This allows vehicle wiring to be reduced and the transmission and reception of multiple signals over a single wire. The messages carried on a Class II serial data streams are also prioritized. If two messages attempt to establish communications on the data line at the same time, the message with a higher priority will continue. The message with a lower priority will wait. If a module cannot respond to the PCM, a DTC will set.

DTC will set when ignition is on, system voltage is greater than 8.2 volts, PCM cannot communicate with EBCM and conditions are present longer than 5 seconds.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(ref-132811-S27457185922002013000000) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Check if scan tool can display data from PCM. If data is displayed, go to next step. If data cannot be displayed, diagnose data link connector.
Check an intermittent, short, or open connection on serial data circuit to EBCM. Repair as necessary. After repairs, go to step 6 . If circuit is okay, go to next step.
Check an intermittent, short, or open connection on serial data circuit to BFC. Repair as necessary. After repairs, go to step 6 . If circuit is okay, go to next step.
Check for DTCs or communication with other modules. Repair as necessary. After repairs, go to next step.
Using scan tool, clear DTCs. Start and warm engine to normal operating temperature. Operate vehicle within conditions for setting this DTC. If scan tool indicates that this diagnostic ran and passed, go to next step. If scan tool does not indicate that this diagnostic ran and passed, repeat step 2 .
Check if any additional DTCs are set. Diagnose affected DTCs. If DTCs are not set, system is okay.

An intermittent may be caused by a poor connection, rubbed-through wire insulation or a broken wire inside the insulation.

DTC P1602: LOSS OF EBTCM SERIAL DATA (4.0L "G" BODY & 4.6L "E" & "K" BODIES)

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

This test checks for absent or invalid EBTCM serial data to the PCM. When such conditions exists for 11 seconds, DTC will set.

Perform On-Board Diagnostic (OBD) system check. See ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, diagnose ABS/TCS system. See appropriate ANTI-LOCK article in BRAKES.

DTC P1603: LOSS OF SDM SERIAL DATA (4.6L "E" & "K" BODIES)

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

This test checks for loss or invalid Sensing and Diagnostic Module (SDM) serial data to PCM. DTC will set when such condition exists for one second.

Perform On-Board Diagnostic (OBD) system check. See ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, diagnose SIR system. See MITCHELL® AIR BAG SERVICE & REPAIR MANUAL, DOMESTIC & IMPORTED MODELS.

DTC P1604: LOSS OF INSTRUMENT PANEL CLUSTER (IPC) SERIAL DATA (3.8L "C" BODY)

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

PCM uses the serial data circuit to communicate with various other devices and systems in the vehicle. PCM ensures that communication remains established by monitoring the serial data circuit for state of health messages from other devices using the circuit. If PCM detects a loss of serial data message from Instrument Panel Cluster (IPC), DTC will set.

DTC will set when ignition is on, system voltage is greater than 8.2 volts, PCM detecting a loss of serial data from IPC and conditions are present for longer than 5 seconds.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(ref-132811-S27457185922002013000000) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Using scan tool, attempt to select IPC data. If IPC data can be displayed, go to next step. If data cannot be displayed, go to step 4 .
Turn ignition off. Disconnect harness connectors from PCM and IPC. Check serial data circuit on harness connector for an open between PCM and IPC. Repair as necessary. After repairs, go to step 6 . If circuit is okay, see «DIAGNOSTIC AIDS»(/gmc/savana/i-1996-2002/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p1537-u1193) .
Check serial data circuit for poor connection at IPC. Repair as necessary. After repairs, go to step 6 . If connection is okay, go to next step.
Check serial data circuit for poor connection at PCM. Repair as necessary. After repairs, go to next step. If connection is okay, diagnose IPC assembly.
Using scan tool, review and record FAILURE RECORDS data. Clear DTCs. Operate vehicle within FAILURE RECORDS conditions. Using scan tool, monitor SPECIFIC DTC INFO for DTC P1604. If scan tool indicates that DTC P1604 failed, repeat step 2 . If scan tool does not indicate that DTC P1604 failed, system is okay.

An intermittent may be caused by a poor connection, rubbed-through wire insulation or a broken wire inside the insulation.

DTC P1604: LOSS OF INSTRUMENT PANEL CLUSTER (IPC) SERIAL DATA (4.0L "G" BODY & 4.6L "E" & "K" BODIES)

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

This test checks for loss of or invalid IPC serial data to the PCM. DTC will set when such condition exists for 11 seconds.

Perform On-Board Diagnostic (OBD) system check. See ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, diagnose IPC. See appropriate INSTRUMENT PANELS article in ACCESSORIES & EQUIPMENT.

DTC P1605: HVAC SERIAL DATA CIRCUIT (3.1L "W" BODY - CENTURY ONLY)

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

PCM uses serial data circuit to communicate with various other devices and systems in vehicle. PCM ensures that communication remains established by monitoring the serial data circuit. If PCM detects a loss of serial data message from the HVAC controller, DTC will set.

DTC will set when ignition is on and system voltage is greater than 8.2 volts.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(ref-132811-S27457185922002013000000) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Using scan tool, attempt to select HVAC data. If HVAC data can be displayed, go to next step. If HVAC cannot be displayed, go to step 4 .
Turn ignition off. Disconnect HVAC controller and PCM harness connector. Check serial data circuit for open between HVAC controller and PCM. Repair as necessary. After repairs, go to step 6 . If circuit is okay, go to next step.
Check serial data circuit for poor connection at HVAC controller. Repair as necessary. After repairs, go to step 6 . If circuit is okay, go to next step.
Check serial data circuit for poor connection at PCM. Repair as necessary. After repairs, go to next step. If connection is okay, diagnose A/C-heater system. See appropriate A/C-HEATER SYSTEMS article in AIR CONDITIONING & HEATING.
Review and record scan tool FAILURE RECORDS data. Clear DTC(s). Operate vehicle within the FAILURE RECORDS conditions. Using scan tool, monitor SPECIFIC DTC INFO for DTC P1605. If scan tool indicates that DTC P1605 failed, repeat step 2 . If scan tool does not indicate that DTC P1605 failed, system is okay.

An intermittent maybe caused by a poor connection, rubbed-through wire insulation or a wire broken inside the insulation.

DTC P1605: LOSS OF HVAC SERIAL DATA (3.5L "W" BODY)

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

This test checks for loss of or invalid Heater and A/C (HVAC) programmer serial data to PCM. When such condition exists for 11 seconds, DTC will set.

Perform On-Board Diagnostic (OBD) system check. See ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, diagnose Electronic Climate Control (ECC) or A/C-heater system. See appropriate A/C-HEATER SYSTEMS article in AIR CONDITIONING & HEATING.

DTC P1605: HVAC SERIAL DATA CIRCUIT (3.8L "W" BODY)

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

PCM uses serial data circuit to communicate with various other devices and systems in vehicle. PCM ensures that communication remains established by monitoring the serial data circuit. DTC will set when PCM detects a loss of serial data message from the HVAC controller with ignition on and system voltage greater than 8.2 volts.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(ref-132811-S27457185922002013000000) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Using scan tool, attempt to select HVAC data. If HVAC data can be displayed, go to next step. If HVAC cannot be displayed, go to step 4 .
Turn ignition off. Disconnect HVAC controller and PCM harness connector. Check serial data circuit for open between HVAC controller and PCM. Repair as necessary. After repairs, go to step 6 . If circuit is okay, go to next step.
Check serial data circuit for poor connection at HVAC controller. Repair as necessary. After repairs, go to step 6 . If circuit is okay, go to next step.
Check serial data circuit for poor connection at PCM. Repair as necessary. After repairs, go to next step. If connection is okay, diagnose A/C-heater system. See appropriate A/C-HEATER SYSTEMS article in AIR CONDITIONING & HEATING.
Review and record scan tool FAILURE RECORDS data. Clear DTC(s). Operate vehicle within the FAILURE RECORDS conditions. Using scan tool, monitor SPECIFIC DTC INFO for this DTC. If scan tool indicates that this DTC failed, repeat step 2 . If scan tool does not indicate that this DTC failed, system is okay.

An intermittent maybe caused by a poor connection, rubbed through wire insulation or a wire broken inside the insulation.

DTC P1605: LOSS OF HVAC SERIAL DATA (4.0L "G" BODY & 4.6L "E" & "K" BODIES)

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

This test checks for loss of or invalid Heater and A/C (HVAC) programmer serial data to PCM. DTC will set when such condition exists for 11 seconds.

Perform On-Board Diagnostic (OBD) system check. See ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, diagnose Electronic Climate Control (ECC) or A/C-heater system. See appropriate A/C-HEATER SYSTEMS article in AIR CONDITIONING & HEATING.

DTC P1610: STANDARD BODY MODULE SERIAL DATA CIRCUIT (3.1L "N" & "W" BODIES)

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

A Class II serial data communications system is used on these vehicles to allow various modules to communicate and share information with each other. Each bit of information has 2 lengths, long or short. This allows vehicle wiring to be reduced and the transmission and reception of multiple signals over a single wire. The messages carried on a Class II serial data streams are also prioritized. If two messages attempt to establish communications on the data line at the same time, the message with a higher priority will continue. The message with a lower priority will wait. PCM will set when a module cannot respond to the PCM with ignition on, system voltage is greater than 8.2 volts and PCM cannot communicate with EBCM.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(ref-132811-S27457185922002013000000) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Check if scan tool can display data from PCM. If data is displayed, go to next step. If data cannot be displayed, diagnose data link connector.
Check an intermittent, short, or open connection on serial data circuit to Body Function Controller (BFC). Repair as necessary. After repairs, go to step 6 . If circuit is okay, go to next step.
Check an intermittent, short, or open connection on serial data circuit to BFC. Repair as necessary. After repairs, go to step 6 . If circuit is okay, go to next step.
Check for DTCs or communication with other modules. Repair as necessary. After repairs, go to next step.
Using scan tool, clear DTCs. Start and warm engine to normal operating temperature. Operate vehicle within conditions for setting this DTC. If scan tool indicates that this diagnostic ran and passed, go to next step. If scan tool does not indicate that this diagnostic ran and passed, repeat step 2 .
Check if any additional DTCs are set. Diagnose affected DTCs. If DTCs are not set, system is okay.

Attempting to start vehicle by by-passing the Passlock® system or substituting parts without performing the password learn procedure may set DTC P1631.

If no password is received, DTC P1610, P1626 and P1631 may set. An intermittent may be caused by poor connection, rubbed through wire insulation or a wire broken inside the insulation.

DTC P1610: CLASS II FAILURE WITH BFC (3.4L "N" BODY)

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

A Class II serial data communications system is used to allow various modules to communicate and share information with each other. Each bit of information has 2 lengths, long or short. This allows vehicle wiring to be reduced and the transmission and reception of multiple signals over a single wire. The messages carried on a Class II serial data streams are also prioritized. If 2 messages attempt to establish communications on the data line at the same time, the message with a higher priority will continue. The message with a lower priority will wait. DTC will set when Body Function Controller (BFC) cannot respond to the PCM.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(ref-132811-S27457185922002013000000) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Using scan tool, check if scan tool can display data from PCM. If PCM data is displayed, go to next step. If PCM data cannot be displayed, diagnose Data Link Connector (DLC).
Check an intermittent, short, or open connection on serial data circuit to Body Function Controller (BFC). Repair as necessary. After repairs, go to step 6 . If circuit is okay, go to next step.
Check an intermittent, short, or open connection on serial data circuit to BFC. Repair as necessary. After repairs, go to step 6 . If circuit is okay, go to next step.
Check for DTCs or communication with other modules. Repair as necessary. After repairs, go to next step.
Using scan tool, clear DTCs. Start and warm engine to normal operating temperature. Operate vehicle within conditions for setting this DTC. If scan tool indicates that this diagnostic ran and passed, go to next step. If scan tool does not indicate that this diagnostic ran and passed, repeat step 2 .
Check if any additional DTCs are set. Diagnose affected DTCs. If additional DTCs are not set, system is okay.

Attempting to start vehicle by by-passing the Passlock® system or substituting parts without performing the password learn procedure may set DTC P1631.

If no password is received, DTC P1610, P1626 and P1631 may set. An intermittent may be caused by poor connection, rubbed through wire insulation or a wire broken inside the insulation.

DTC P1610: LOSS OF BCM SERIAL DATA (3.5L "W" BODY)

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

This test checks for loss of or invalid Body Control Module (BCM) serial data to PCM. When such condition exists for 11 seconds, DTC will set.

Perform On-Board Diagnostic (OBD) system check. See ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, check BCM serial data line for open or short to ground.

DTC P1610: STANDARD BODY MODULE SERIAL DATA CIRCUIT (3.8L "C" & "W" BODIES)

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

A serial data communications system is used on these vehicles to allow various modules to communicate and share information with each other. Each bit of information has 2 lengths, long or short. This allows vehicle wiring to be reduced and the transmission and reception of multiple signals over a single wire. The messages carried on a Class II serial data streams are also prioritized. If two messages attempt to establish communications on the data line at the same time, the message with a higher priority will continue. The message with a lower priority will wait. DTC will set when a module cannot respond to the PCM with ignition on, system voltage greater than 8.2 volts and PCM cannot communicate with EBCM for longer than 5 seconds.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(ref-132811-S27457185922002013000000) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Check if scan tool can display data from Body Control Module (BCM). If BCM data is displayed, go to next step. If BCM data cannot be displayed, go to step 4 .
Turn ignition off. Disconnect BCM and PCM harness connectors. Check serial data circuit for open between BCM and PCM. Repair as necessary. After repairs, go to step 6 . If circuit is okay, see «DIAGNOSTIC AIDS»(/gmc/savana/i-1996-2002/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p1537-u1193) .
Check serial data circuit for poor connection at BCM. Repair as necessary. After repairs, go to step 6 . If circuit is okay, go to next step.
Check serial data circuit for poor connection at PCM. Repair as necessary. After repairs, go to next step. If connection is okay, diagnose BCM.
Using scan tool, clear DTCs. Start and warm engine to normal operating temperature. Operate vehicle within conditions for setting this DTC. If scan tool indicates that this diagnostic ran and passed, system is okay. If scan tool does not indicate that this diagnostic ran and passed, repeat step 2 .

An intermittent may be caused by poor connection, rubbed-through wire insulation or a wire broken inside the insulation.

DTC P1610: LOSS OF PZM SERIAL DATA (4.6L "E" & "K" BODIES)

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

This test checks for loss of or invalid Platform Zone Module (PZM) serial data to PCM. DTC will set when such condition exists for 11 seconds.

Perform On-Board Diagnostic (OBD) system check. See ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, check PZM serial data line for open or short to ground.

DTC P1611: LOSS OF CVRTD SERIAL DATA (4.6L "E" & "K" BODIES)

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

This test checks for absent or invalid Continuous Variable Real Time Damping (CVRTD) system serial data to PCM. DTC will set when such condition exists for 11 seconds.

Perform On-Board Diagnostic (OBD) system check. See ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, check CVRTD system serial data line for open or short to ground.

DTC P1612: LOSS OF IPM SERIAL DATA (4.6L "K" BODY - SEVILLE)

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

This test checks for absent or invalid Instrument Panel Module (IPM) serial data to PCM. DTC will set when such condition exists for 11 seconds.

Perform On-Board Diagnostic (OBD) system check. See ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, check IPM system serial data line for open or short to ground.

DTC P1613: LOSS OF DIM SERIAL DATA (4.6L "K" BODY - SEVILLE)

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

This test checks for absent or invalid Driver's Integration Module (DIM) serial data to PCM. DTC will set when such condition exists for 11 seconds.

Perform On-Board Diagnostic (OBD) system check. See ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, check DIM system serial data line for open or short to ground.

DTC P1614: LOSS OF RIM SERIAL DATA (4.6L "K" BODY - SEVILLE)

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

This test checks for absent or invalid Rear Integration Module (DIM) serial data to PCM. DTC will set when such condition exists for 11 seconds.

Perform On-Board Diagnostic (OBD) system check. See ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, check RIM system serial data line for open or short to ground.

DTC P1615: LOSS OF VTD SERIAL DATA (4.6L "K" BODY - SEVILLE)

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

This test checks for absent or invalid Vehicle Theft Deterrent (VTD) module serial data to PCM. DTC will set when such condition exists for 11 seconds.

Perform On-Board Diagnostic (OBD) system check. See ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, check VTD system serial data line for open or short to ground.

Oil level switch is a magnetic reed float style switch which is closed when oil level is full and open when oil level is low. This test monitors oil level switch input signal. If test conditions are met and switch indicates oil level full with no transition of oil level switch for a specific length of time, DTC will set.

Conditions for setting DTC are: engine is running, vehicle speed is 3 MPH or greater and engine speed is greater than 2000 RPM.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(ref-132811-S27457185922002013000000) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Check engine oil level. If engine oil is higher than normal level, go to step 7 . If engine oil level is okay, go to next step.
Install scan tool. Start engine. Ensure transmission is in Park. Using scan tool, view engine oil level. Increase engine speed to 2000 RPM. If scan tool indicates that oil level is low, fault is not present. If scan tool indicates that oil level is not low, go to next step.
Disconnect oil level switch connector. If scan tool indicates that oil level is low, go to step 8 . If scan tool indicates that oil level is not low, go to next step.
Using scan tool, record oil life index. Turn ignition off. Wait 30 seconds, then disconnect PCM harness connector C2. Using DVOM, check resistance between ground and PCM harness connector C2 terminal No. 58. If resistance is 10,000 ohms or less, go to next step. If resistance is not 10,000 ohms or less, go to step 9 .
Repair short to ground in oil level input circuit.
Drain excess engine oil.
Replace engine oil level switch.
Replace PCM. Program replacement PCM using required equipment.

DTC P1619: ENGINE OIL LIFE MONITOR RESET CIRCUIT (3.8L "H" BODY)

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

To determine engine oil life remaining, PCM monitors ECT, number of crankshaft revolutions, vehicle speed, and calculated oil temperature. When PCM determines oil is at end of useful life, it will send a signal through Serial Data Line (SDL) to illuminate CHANGE OIL SOON indicator.

DTC will set when Oil Life Monitor (OLM) reset circuit is grounded for greater than 60 seconds.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(ref-132811-S27457185922002013000000) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Turn ignition on. Using scan tool, observe OIL LIFE SWITCH. If scan tool displays PRESSED, go to next step. If scan tool does not display PRESSED, see «DIAGNOSTIC AIDS»(/gmc/savana/i-1996-2002/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p1537-u1193) .
Turn ignition off. Disconnect PCM connectors. Turn ignition on. Connect a test light between battery voltage and PCM harness connector OLM reset circuit. If test light illuminates, go to next step. If test light does not illuminate, go to step 6 .
Disconnect OLM reset switch. Connect a test light between battery voltage and PCM harness connector OLM reset circuit. If test light illuminates, go to next step. If test light does not illuminate, go to step 7 .
Locate and repair short to ground in OLM reset circuit. After repairs, go to step 8 .
Replace PCM. Program replacement PCM using required equipment. After replacing PCM, go to step 8 .
Replace OLM reset switch. After replacing switch, go to next step.
Turn ignition on. Using scan tool, observe OIL LIFE SWITCH. If scan tool displays PRESSED, return to step 3 . If scan tool does not display PRESSED, repair is complete.

Check for faulty connections or damaged harness. Connect a DVOM between battery voltage PCM harness connector OLM reset circuit. Observe DVOM while moving all related harnesses and connectors. A change in voltage display indicates fault location.

DTC P1620: LOW COOLANT LEVEL CIRCUIT (1.9L SATURN)

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

PCM monitors the 12 volt signal from the low coolant switch. When switch opens, indicating low coolant condition, PCM will not detect the 12 volt signal.

DTC will set if coolant switch opens (low signal) for 20 seconds, with engine running. Low coolant circuit is continuously checked when engine is running.

Ensure coolant level is okay, add if necessary. Check coolant level reading using scan tool. If scan tool indicates that coolant level is okay, problem is intermittent. See «DIAGNOSTIC AIDS»(/gmc/savana/i-1996-2002/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p1537-u1193) . If scan tool indicates that coolant level is low, go to next step.
Check if back-up lights are operating properly. If back-up lights illuminate, go to next step. If back-up lights does not illuminate, check back-up light or fuse. Replace as necessary. If fuse is faulty, check for short in circuit. If fuse is okay, check for open in circuit.
Remove coolant recovery tank. Disconnect coolant level switch. Using a jumper wire, jumper coolant level switch terminals together. Observe status on scan tool. If scan tool indicates low coolant, go to next step. If scan tool does not indicate low coolant, replace coolant level switch.
Disconnect jumper wire. Using test light connected to ground, probe low coolant level switch harness connector terminal "B". If test light illuminates, go to next step. If test light does not illuminate, repair open in circuit to switch.
Using test light connected to battery voltage, probe low coolant switch terminal "A". If test light illuminates, repair short to ground in circuit. If test light does not illuminate, check for open in circuit.

The low coolant switch is a normally closed switch when coolant in reservoir bottle is at proper level. Pressure check engine for leaks. The LOW COOLANT/HOT light will flash coolant when switch is open.

DTC will set when PCM determines that a memory error exists.

Reprogram PCM. If DTC P1621 resets, replace PCM. Program replacement PCM using required equipment.

PCM is the control center of the fuel injection system. It constantly looks at information from various sensors, and controls the systems that affect vehicle performance. PCM also performs the diagnostic function of the system. If can recognize operational problems, alert the driver through the MIL, and store DTC(s).

DTC will set when PCM cannot communicate internally.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(ref-132811-S27457185922002013000000) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Replace PCM. Program replacement PCM using required equipment. After replacing PCM, go to next step.
Using scan tool, CLEAR INFO or CLEAR DTCs function to clear DTC. Start and warm engine to normal operating temperature. Operate vehicle within the conditions foe setting DTC. If scan tool indicates that diagnostic ran and passed, go to next step. If scan tool does not indicate that diagnostic ran and passed, repeat step 2 .
Check if any additional DTC(s) are present. If additional DTCs are present, diagnose affected DTC(s) first. If no other DTCs are present, system is okay.

EEPROM is a data storage unit which can save critical data even battery power is removed. This is used by PCM to store TP sensor idle learned values, transaxle adapt values, transaxle oil life index and cruise control lash/learn.

The EEPROM has several locations available to store this information. If PCM detects a problem in one location of the EEPROM, it will store data in another location. If PCM runs out of good locations in EEPROM to store data, DTC will set.

The PCM stores the same data in its Keep Alive Memory so that even if EEPROM is bad and DTC is set, the operator will not notice any difference in vehicle operation. Even after DTC sets, PCM will continue to look for good locations in EEPROM in which to store data and if it finds one, DTC will become a history code. EEPROM is soldered into PCM and cannot be serviced. If a current DTC P1621 is set, PCM must be replaced.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(ref-132811-S27457185922002013000000) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Turn ignition on. Using scan tool, select DTC INFO and select FAIL THIS IGN. If DTC failed this ignition cycle, go to step 4 . If DTC did not fail in this ignition cycle, go to next step.
Clear DTC P1621. Cycle ignition on and off several times slowly. Turn ignition on for 10 seconds, then turn ignition off for 30 seconds. Using scan tool, view DTC INFO and select TEST FAIL SCC. If this DTC failed since DTCs were cleared, go to next step. If no, fault is not present.
Replace PCM. Program replacement PCM using required equipment.

DTC P1621: VCM EEPROM PERFORMANCE (4.3L "C", "K", "L", "M", "S" & "T" SERIES)

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

The VCM EEPROM contains data essential to running the engine and transmission. VCM program stores this data in the EEPROM. This data remains in the EEPROM even if battery is disconnected. At power-up, VCM checks the integrity of this data. If the checksum of the EEPROM does not match a predetermined value, DTC will set. DTC will also set if VCM is unable to correctly read data from EEPROM memory.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(ref-132811-S27457185922002013000000) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Replace VCM. Program replacement VCM using required equipment and perform Crankshaft Variation Learn Procedure. After replacing VCM, go to next step.
Using scan tool, select DTC and CLEAR DTC INFO function. Warm engine to normal operating temperature. Operate engine at idle. Using scan tool, select DTC and SPECIFIC DTC function, then enter this DTC. Operate vehicle within conditions for setting this DTC. If scan tool indicates that this DTC ran and passed, go to next step. If scan tool does not indicate that this DTC ran and passed, repeat step 2 .
Check if any additional DTC(s) are present. If additional DTCs are present, diagnose affected DTC(s) first. If no other DTCs are present, system is okay.

Replace VCM even if this DTC exists only in history.

DTC P1621: VCM EEPROM PERFORMANCE (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.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(ref-132811-S27457185922002013000000) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Replace VCM. Program replacement VCM using required equipment and perform Crankshaft Variation Learn Procedure. After replacing VCM, go to next step.
Using scan tool, select DTC and CLEAR DTC INFO function. Warm engine to normal operating temperature. Operate engine at idle. Using scan tool, select DTC and SPECIFIC DTC function, then enter this DTC. Operate vehicle within conditions for setting this DTC. If scan tool indicates that this DTC ran and passed, go to next step. If scan tool does not indicate that this DTC ran and passed, repeat step 2 .
Check if any additional DTC(s) are present. If additional DTCs are present, diagnose affected DTC(s) first. If no other DTCs are present, system is okay.

Replace VCM even if this DTC exists only in history.

DTC indicates a fault with the PCM pull-up resistor used to revise ECT resolution throughout the entire engine operating conditions. This DTC requires cold start (IAT=ECT) to be able to detect fault.

Record and diagnose all DTC(s) present. If DTC P1623 resets, replace PCM. Program replacement PCM using required equipment.

PCM has the capability of running a "Customer Snap Shot" function to aid in diagnosing intermittent problems. With this feature, the technician has the ability to capture engine general information parameters when experiencing driveability concerns to aid in diagnosis. If vehicle is equipped with cruise control, activation of the function is accomplished simply by toggling the on/off cruise control switch 3 times within 3 seconds. The PCM looks for 3 transitions either off or on within 3 seconds to capture the data. The PCM then sets DTC P1624 and information is stored in the malfunction history. The malfunction history can be accessed using a scan tool. The PCM will only allow one snap shot per ignition cycle.

This DTC will set when TC determines that its flash memory has failed.

Record and diagnose all DTC(s). Clear DTC(s). If DTC P1625 resets, replace PCM. Program replacement PCM using required equipment.

DTC P1626: LOSS OF SERIAL COMMUNICATION WITH VEHICLE THEFT DETERRENT OR THEFT DETERRENT SYSTEM FUEL ENABLE CIRCUIT (2.2L "S" SERIES & 2.4L "J" & "N" BODIES)

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

A Class II serial data communications system is used in order to allow various modules to communicate and share information with each other. Messages carried on the Class II data stream are also prioritized. If 2 messages attempt to establish communications on the data line at the same time, the message with lower priority will have to wait.

DTC will set when PCM has lost communication with Body Function Controller (BFC) after PCM received a theft passed message from BFC.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(ref-132811-S27457185922002013000000) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Using scan tool, check if DTC U1064 is also set. If DTC U1064 is set, diagnose DTC U1064 first. If DTC U1064 is not set, go to next step.
Check if any of vehicle theft deterrent system has been tampered with. If theft deterrent system has been tampered, go to next step. If no components were tampered, go to step 5 .
Repair tampered components. After repairs, perform Passlock® password learn procedure. After performing learn procedure, go to step 8 .
If Body Function Controller (BFC) indicates that password is valid, go to next step. If BFC indicates that password is not valid, go to step 7 .
Replace PCM. Program replacement PCM using required equipment. After replacing PCM, go to next step.
Check for BFC related DTCs. Diagnose DTC as necessary. After repairs, go to next step.
Using scan tool, CLEAR INFO or CLEAR DTCs function to clear DTC. Start and warm engine to normal operating temperature. Operate vehicle within conditions for setting this DTC. If scan tool indicates that this diagnostic ran and passed, go to next step. If scan tool does not indicate that this diagnostic ran and passed, repeat step 2 .
Check if any additional DTCs are set. Diagnose affected DTCs. If no additional DTCs are not set, system is okay.

Attempting to start vehicle by by-passing theft deterrent system or substituting part without performing the password learn procedure may set this DTC. If no password is received, DTC P1631 and P1632 may be set.

DTC P1626: THEFT DETERRENT SYSTEM FUEL ENABLE CIRCUIT (3.1L "N" BODY)

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

Vehicle Theft Deterrent (VTD) module produces a theft deterrent fuel enable signal when ignition is on and proper key resistor pellet is sensed by VTD module. Powertrain Control Module (PCM) monitors fuel enable signal during cranking.

DTC will set when engine is running, PCM detects fuel enable signal is not present or incorrect, PCM cannot communicate with theft deterrent system and conditions are present longer than 2 seconds.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(ref-132811-S27457185922002013000000) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Using scan tool, check if DTC P1610 is also set. If DTC P1610 is set, diagnose DTC P1610 first. If DTC P1610 is not set, go to next step.
Check if any of vehicle theft deterrent system has been tampered with. If theft deterrent system has been tampered, go to next step. If no components were tampered, go to step 5 .
Repair tampered components. After repairs, perform Passlock® password learn procedure. After performing learn procedure, go to step 8 .
If Body Function Controller (BFC) indicates that password is valid, go to next step. If BFC indicates that password is not valid, go to step 7 .
Replace PCM. Program replacement PCM using required equipment. After replacing PCM, go to next step.
Check for BFC related DTCs. Diagnose DTC as necessary. After repairs, go to next step.
Using scan tool, CLEAR INFO or CLEAR DTCs function to clear DTC. Start and warm engine to normal operating temperature. Operate vehicle within conditions for setting this DTC. If scan tool indicates that this diagnostic ran and passed, go to next step. If scan tool does not indicate that this diagnostic ran and passed, repeat step 2 .
Check if any additional DTCs are set. Diagnose affected DTCs. If additional DTCs are not set, system is okay.

DTC P1626: THEFT DETERRENT SYSTEM FUEL ENABLE CIRCUIT (3.1L "W" BODY)

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

The Vehicle Theft Deterrent (VTD) system is incorporated into the Body Control Module (BCM). PCM monitors the state of serial data message from the VTD system to ensure that PCM to BCM communications is established. DTC will set if PCM detects a loss of communication while engine is running.

DTC P1626 can cause a no-start condition or normal operation depending on when the loss of VTD system communication was detected. Engine will continue to start and run if the condition that set DTC occurred after the PCM received a valid VTD password from BCM and already allowed fuel during the ignition cycle. Engine will start and immediately stall if the condition that set DTC occurred before PCM received a valid VTD password. With this condition present, PCM will inhibit fuel delivery and disable starter until a valid VTD password is detected.

DTC will set when VTD system has allowed fuel delivery, PCM detects an incorrect theft deterrent fuel enable signal from VTD system and conditions are present for longer than 2 seconds.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(ref-132811-S27457185922002013000000) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Attempt to select vehicle theft deterrent system data with scan tool. If data can be displayed, go to next step. If data cannot be displayed, go to step 5 .
Turn ignition off. Disconnect PCM and BCM harness connectors. Check serial data circuit for an open between BCM and PCM. Repair as necessary. After repairs, go to step 6 . If circuit is okay, go to next step.
Check serial data circuit for poor connections at PCM. Repair as necessary. After repairs, go to step 6 . If problem is found, see «DIAGNOSTIC AIDS»(/gmc/savana/i-1996-2002/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p1537-u1193) .
Check serial data circuit for poor connections at BCM. Repair as necessary. After repairs, go to next step. If circuit is okay, diagnose theft deterrent system.
Using scan tool, review and record scan tool FAILURE RECORDS data. Clear DTC. Attempt to start engine. If engine starts and continues to run, system is okay. If engine does not start or starts and then stalls, repeat step 2 .

An intermittent may be caused by poor connection, rubbed through wire insulation, or a wire broken inside insulation. Reviewing the FAILURE RECORDS vehicle mileage since the diagnostic test last failed may help determine how often the condition that caused the DTC to be set occurs.

DTC P1626: THEFT DETERRENT SYSTEM FUEL ENABLE CIRCUIT (3.4L "N" BODY)

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

DTC will set when PCM cannot communicate with the theft deterrent system.

Perform «DIAGNOSTIC AIDS»(/gmc/savana/i-1996-2002/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p1537-u1193__dtc-p1626-theft-deterrent-system-fuel) . After performing OBD system check, go to next step.
Using scan tool, check if DTC P1610 is also set. If DTC P1610 is set, diagnose DTC P1610 first. If DTC P1610 is not set, go to next step.
Check if any part of the vehicle theft deterrent system has been tampered. If theft deterrent system has been tampered, go to next step. If theft deterrent system has not been tampered, go to step 5 .
Repair tampered component. After repairs, perform Passlock® learn procedure, then go to step 8 .
Check if Body Function Controller (BFC) indicates that password is valid. If password is valid, go to next step. If password is not valid, go to step 7 .
Replace PCM. Program replacement PCM using required equipment. After replacing PCM, go to step 8 .
Check for BFC related DTCs. Repair as necessary. After repairs, go to next step.
Using scan tool, select CLEAR INFO or CLEAR DTCs function to clear DTCs. Start and operate engine to normal operating temperature. Operate vehicle within conditions for setting this DTC. If scan tool indicates that this diagnostic ran and passed, go to next step. If scan tool does not indicate that this diagnostic ran and passed, repeat step 2 .
Using scan tool, check if any additional DTCs are set. Diagnose affected DTCs. If no additional DTCs are not set, system is okay.

DTC P1626: THEFT DETERRENT SYSTEM FUEL ENABLE CIRCUIT (3.4L "U" SERIES)

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

DTC will set when engine is running, PCM detects fuel enable signal is not present or incorrect and conditions are present longer than 2 seconds.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(ref-132811-S27457185922002013000000) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Ensure battery is fully charged. Attempt to start engine. If engine cranks, go to next step. If engine does not crank, see appropriate ANTI-THEFT SYSTEMS article in ACCESSORIES & EQUIPMENT.
Turn ignition off. Disconnect VTD module. Turn ignition on. Using DVOM, check voltage between ground circuit and fuel enable circuit at VTD module harness connector. If voltage reading is about 5 volts, go to next step. If voltage reading is not about 5 volts, go to step 6 .
Turn ignition off. Reconnect VTD module connector. Turn ignition on. Backprobing connector, check frequency between ground and fuel enable circuit terminal at VTD module connector. If frequency is 40-60 Hz, go to next step. If frequency is not 40-60 Hz, go to step 8 .
Using scan tool, select CLEAR INFO or CLEAR DTCs function to clear DTC P1626. Attempt to start engine. If engine starts and continues to run, see «DIAGNOSTIC AIDS»(/gmc/savana/i-1996-2002/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p1537-u1193) . If engine does not start or starts but does not continue to run, go to step 7 .
Check for an open, short to ground or short to voltage in fuel enable circuit. Repair as necessary. After repairs, go to step 11 . If circuit is okay, go to next step.
Check fuel enable circuit for poor terminal connection at PCM connector. Repair as necessary. After repairs, go to step 11 . If connection is okay, go to step 9 .
Check for poor terminal connections at VTD module connector. Repair as necessary. After repairs, go to step 11 . If terminals are okay, go to step 10 .
Replace PCM. Program replacement PCM using required equipment. After replacing PCM, go to step 11 .
Replace VTD module. After repair is completed, go to next step.
Using scan tool, CLEAR INFO or CLEAR DTCs function to clear DTC P1554. Using scan tool, select ENG 2 data list. Observe VTD FUEL DISABLE display. If reading indicates inactive, repair is complete. If reading does not indicate inactive, repeat step 2 .

DTC P1626: LOSS OF SERIAL COMMUNICATION WITH VEHICLE THEFT DETERRENT SYSTEM (3.5L "W" BODY)

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

This test checks for loss of or invalid theft deterrent system serial data to the PCM. DTC will set when this condition is present for 11 seconds.

If DTC sets after engine is already running, engine will continue to run and will continue to start on subsequent drive trips as long as battery is not disconnected. If DTC sets at PCM power-up, starter and engine fueling will be disabled.

Perform On-Board Diagnostic (OBD) system check. See ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, diagnose theft deterrent system. See appropriate ANTI-THEFT SYSTEMS article in ACCESSORIES & EQUIPMENT.

Vehicle operation is disabled if incorrect key or starting procedure is used. Theft deterrent module enables crank circuit to starter and sends a signal to PCM if correct key is being used. If proper signal does not reach PCM fuel enable signal circuit, PCM will not pulse injectors on, disabling vehicle, even if crank circuit is by-passed. Signal should be 40-60 Hz and is measured using DVOM in Hertz scale.

Conditions required to set DTC are, engine running, PCM detects incorrect signal on Theft Deterrent System (TDS) fuel enable circuit and conditions are present for greater than 2 seconds.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(ref-132811-S27457185922002013000000) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Ensure battery is fully charged. Crank engine. If engine cranks, go to next step. If engine does not crank, diagnose and repair Theft Deterrent System (TDS).
Turn ignition off. Disconnect Vehicle Theft Deterrent (VTD) module connector. Turn ignition on. Using a DVOM, check voltage between VTD module harness connector ground and VTD fuel enable circuits. If voltage reading is about 5 volts, go to next step. If voltage reading is not about 5 volts, go to step 6 .
Turn ignition off. Reconnect VTD connector. Turn ignition on. Using DVOM in Hertz (Hz) scale, check frequency between engine ground and VTD fuel enable circuit. If frequency is 40-60 Hz, go to next step. If frequency is not 40-60 Hz, go to step 8 .
Turn ignition off. Using scan tool, clear DTCs. Attempt to start engine. If engine starts and continues to run, see «DIAGNOSTIC AIDS»(/gmc/savana/i-1996-2002/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p1537-u1193) . If engine does not start, go to step 7 .
Check TDS fuel enable circuit for open, short to ground or short to battery voltage. Repair as necessary. After repairs, go to step 11 . If no problem is found, go to next step.
Check VTD fuel enable circuit for faulty connection at PCM. Repair as necessary. After repairs, go to step 11 . If VTD fuel enable circuit connection at PCM is okay, go to step 9 .
Check for faulty connection at TDS module. Repair as necessary. After repairs, go to step 11 . If connection is okay, go to step 10 .
Replace PCM. Program replacement PCM using required equipment. After replacing PCM, go to step 11 .
Replace VTD module. After replacing module, go to next step.
Clear DTCs. Turn ignition on and observe VTD FUEL DISABLE scan tool display. If scan tool displays INACTIVE, repair is complete. If scan tool does not display INACTIVE, return to step 2 .

Check for faulty connections or damaged harness. Disconnect VTD module connector. Turn ignition on. Connect a DVOM between engine ground and VTD module harness connector fuel enable circuit. Observe DVOM while moving all related harness and connectors. A change in voltage display indicates fault location.

DTC P1626: THEFT DETERRENT SYSTEM FUEL ENABLE CIRCUIT (4.0L "G" BODY)

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

This DTC is an indication that fuel enable input to PCM has failed in a given cycle. The PASS-Key® system enables engine operation by allowing starter to engage and issuing a fuel enable signal to PCM. If a failure is present at the end of the fuel decision point, a no start condition can be caused. Additionally, PCM will not disable fuel injection after is has been enabled within a given ignition cycle to prevent stalling as a result of PASS-Key® system failure.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(ref-132811-S27457185922002013000000) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Attempt to start engine. If engine cranks, go to next step. If engine does not crank, check starting system. See appropriate STARTERS article in STARTING & CHARGING SYSTEMS.
Turn ignition off. Disconnect PASS-Key® module harness connector. Turn ignition on. Using DVOM, check voltage between ground and PASS-Key® module fuel enable input circuit at harness connector terminal. If voltage reading is 2-6 volts, go to next step. If voltage reading is not 2-6 volts, go to step 6 .
Turn ignition off. Reconnect PASS-Key® module harness connector. Turn ignition on. Measure DC frequency between PASS-Key® module fuel enable input circuit terminal and ground. If frequency reading is 40-60 Hz, go to next step. If frequency reading is not 40-60 Hz, go to step 8 .
Clear DTC. Attempt to start engine. If engine starts, fault is not present. If engine does not start, go to step 12 .
Store fluid life index as indicated on scan tool. Turn ignition off and wait 30 seconds, then disconnect PCM harness connector C1. Using DVOM, check resistance of PASS-Key® fuel enable circuit between PCM harness connector C1 and PASS-Key® module harness connector terminals. If resistance is 5 ohms or less, go to next step. If resistance is greater than 5 ohms, go to step 10 .
Check resistance between ground and PASS-Key® fuel enable input circuit at PCM harness connector terminal. If resistance is greater than 10,000 ohms, go to step 12 . If resistance is not greater than 10,000 ohms, go to step 11 .
Check terminal contact at PASS-Key® module harness connector. Repair as necessary. If terminal contacts are okay, go to next step.
Replace PASS-Key® module.
Repair open in fuel enable input circuit.
Repair short to ground in fuel enable input circuit.
Check terminal contact at PCM harness connector C1. Repair as necessary. If terminal contact is okay, go to next step.
Replace PCM. Program replacement PCM using required equipment.

An intermittent setting of DTC P1626 could be caused by an intermittent open/short to ground or short to voltage in fuel enable input circuit.

An intermittent no-start could be caused by loss of power or ground to the PASS-Key® module. Since the module samples the ignition key resistor pellet only once per ignition cycle (at key on), faults of the PASS-Key® system cannot cause a stalling problem.

DTC P1626: LOSS OF SERIAL COMMUNICATION WITH VTD (4.3L "C", "K", "L", "M", "S" & "T" SERIES)

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

A Class II serial data circuit is used in communication between VCM and Vehicle Theft Deterrent (VTD) system. VTD sends a Vehicle Security Password (VSP) when ignition 1 input becomes active and includes its source ID. The VSP includes either a fuel continue or fuel disable password.

When Passlock® portion of VTD system has sensed the proper operation of the ignition switch and lock, the system transmits a password to the VCM. VCM enables fuel delivery if this password matches the password stored in VCM's memory.

If communication is lost or a VTD failure occurs (during an ignition cycle that VCM has enabled fuel), VCM will enter a fail-safe/fail enable mode. VCM remains in fail enable mode for the current and future ignition cycles, until fault is corrected and a valid password is received, or until battery power is removed. If battery power is removed while VCM is in fail enable mode, VCM disables fuel delivery. Vehicle will not start or will start then stall.

When VCM receives a invalid password or no password before the fuel disable decision point, VCM disables fuel delivery. Fuel disable decision point occurs at about 300 RPM during engine crank mode.

DTC will set when VCM has established communications and received VSP during current ignition cycle from VTD control module or VCM cannot establish communications with VTD control module and has not received a valid password before fuel disable decision point.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(ref-132811-S27457185922002013000000) 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, attempt to establish communications with VTD control module. If scan tool communicates with VTD control module, go to next step. If scan tool cannot communicate with VTD control module, diagnose VTD system. See appropriate ANTI-THEFT SYSTEMS article in ACCESSORIES & EQUIPMENT.
Check Class II serial data circuit for open, short or faulty connection between VTD control module and VCM. Repair as necessary. After repairs, go to step 6 . If circuit or connections are okay, go to next step.
Turn ignition off. Reconnect all components that were disconnected earlier. Turn ignition on, engine off. Using scan tool, clear all DTCs. Turn ignition off for about 15 minutes. Attempt to start engine. Check if DTC resets. If DTC resets, diagnose theft deterrent system. See appropriate ANTI-THEFT SYSTEMS article in ACCESSORIES & EQUIPMENT. If DTC does not reset, go to next step.
This DTC is intermittent. If DTC additional DTCs are stored, diagnose affected DTC. If no other DTCs are is intermittent, see «DIAGNOSTIC AIDS»(/gmc/savana/i-1996-2002/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p1537-u1193) .
Repair as necessary. After repairs, go to next step.
Turn ignition off. Reconnect or reinstall components that were previously disconnected/removed. Using scan tool, clear DTCs. Check if additional DTCs are present. Diagnose affected DTCs. If no additional DTCs are present, system is okay.

DO NOT clear DTCs unless directed by diagnostic procedure. Clearing DTCs will also clear valuable FREEZE FRAME and FAILURE RECORDS data. An intermittent may be caused by a poor connection, rubbed-through wire insulation or a broken wire inside insulation. Check circuits and terminals that can cause an intermittent condition.

DTC P1626: THEFT DETERRENT SYSTEM FUEL SIGNAL LOST (4.6L "E" & "K" BODIES)

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

After the key resistor pellet has been confirmed by the PASS-Key® portion of the Vehicle Theft Deterrent (VTD) system, the IPC sends a password to the PCM via the Class II serial data bus. If password matches the password stored in the PCM, fuel will be enabled. If IPC does not send a password or if PCM does not receive it, vehicle will not start unless VTD has the fuel enabled.

If IPC and PCM loose communication with each other while engine is running, VTD system will fail-enable and allow driver to restart the vehicle on future ignition cycles until communications between the IPC and PCM are restored. If battery is disconnected during this period, vehicle will loose its fail-enabled status and will no longer start until communications has been re-established.

If IPC and PCM loose communications with each other while engine is not running, VTD system will disable fuel until communications is restored to prevent vehicle theft.

In both cases, DTC P1626 will be set. The PCM will not disable fuel injection once it has been enabled within a given ignition cycle to prevent stalling as a result of VTD system faults.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(ref-132811-S27457185922002013000000) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Check if DTC P1604 is also present. If DTC P1604 is present, diagnose using P1604 tests. If DTC P1604 is not present, go to next step.
Check for VTD or IPC DTCs. If DTCs are present, diagnose DTCs first. If DTCs are not present, see «DIAGNOSTIC AIDS»(/gmc/savana/i-1996-2002/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p1537-u1193) .

The most likely cause of DTC P1626 is a loss of serial data communication to the IPC. Check for loss of power to IPC or for other causes of communication loss.

DTC P1626: THEFT DETERRENT SYSTEM FUEL ENABLE CIRCUIT (4.8L, 5.3L & 6.0L "C" & "K" SERIES)

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

The Vehicle Theft Deterrent (VTD) system consists of PCM, BCM and ignition lock. After the BCM has confirmed the proper voltage from the ignition switch, BCM sends a password to the PCM through the Class II serial data circuit. When password matches the password stored in the PCM, the system enables the fuel. If BCM does not send a password or PCM does not receive it, vehicle will not start unless the PCM is in VTD fail-enabled mode. If BCM and PCM loose communications with each other after system has received the correct password, PCM goes into VTD fail-enabled mode, allowing driver to restart vehicle on future ignition cycles until communications between BCM and PCM are restored.

If BCM and PCM loose communications before the PCM receives the BCM password, PCM will disable fuel until communications is restored in order to prevent vehicle theft. PCM will not disable fuel injection once the PCM enabled the fuel within a given ignition cycle in order to prevent stalling as a result of VTD system faults.

DTC will set when PCM does not receive the password messages from the BCM prior to the VTD fuel decision point.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(ref-132811-S27457185922002013000000) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Crank engine. If engine starts and runs, go to next step. If engine does not start, diagnose VTD system.
Using scan tool, check if PCM is in VTD Fail-Enabled mode. If VTD is in fail-enabled mode, go to next step. If VTD is not in fail-enabled mode, see «DIAGNOSTIC AIDS»(/gmc/savana/i-1996-2002/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p1537-u1193) .
Turn ignition off. Disconnect battery positive battery cable for one minute. Reconnect battery cable. Attempt to start engine. If engine starts and idles, see «DIAGNOSTIC AIDS»(/gmc/savana/i-1996-2002/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p1537-u1193) . If engine does not start, go to next step.
Using scan tool, check if this DTC is set. If this DTC is set, diagnose VTD system. If this DTC is not set, diagnose engine no-start condition.

Most likely cause of DTC P1626 is loss of serial data communication from BCM. Check for loss of power to BCM. Check serial data circuit for open, short to ground or short to voltage.

DTC P1626: THEFT DETERRENT FUEL ENABLE SIGNAL NOT RECEIVED (5.0L & 5.7L "C" & "K" SERIES)

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

The control module communicates with other modules using the Class 2 Serial Data circuit. The Vehicle Theft Deterrent (VTD/Passlock®) module sends a vehicle security password to the control module, via the Class 2 Serial Data circuit, after the system has sensed the proper operation of the ignition switch and lock, and determined that the switch and lock have not been tampered with. If this password matches the password stored in the control module, fuel will be enabled. If the VTD (Passlock) module does not send a password, or if the control module does not receive it, vehicle will not start, or it may start and stall. This will set a DTC P1626 in the control module memory. If communication is lost after receiving the password, the VTD (Passlock) system will go into Fail Enable, set a U1192 in the control module, and engine will continue to run. This will allow the engine to restart on future ignition cycles but may set a DTC P1626 as engine is started. If battery is disconnected or the codes are cleared, vehicle will lose its Fail Enable status and will not start until communication is re-established.

Note. Before clearing the DTCs, use scan tool Capture Info to save the Freeze Frame and Failure Records for reference. The control module's data is deleted once the Clear Info function is used.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(ref-132811-S27457185922002013000000) 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, attempt to establish communications with the VTD (Passlock) Control Module. Does the scan tool communicate with the VTD (Passlock) Control Module? If yes, go to next step. If no, see appropriate ANTI-THEFT SYSTEMS article in ACCESSORIES & EQUIPMENT.
Check the Class 2 Serial Data circuit for an open in the Class 2 Serial Data circuit between VCM and VTD (Passlock) Control Module, a short to ground, short to voltage, or loose/damaged terminals at DLC, VCM or VTD (Passlock) Control Module. Did you find a problem? If yes, go to step 6 . If no, go to next step.
Turn ignition off. Connect or install any connectors or components that were disconnected or removed. Clear all DTCs using scan tool. Turn ignition off for 15 seconds. Attempt to start engine. Does DTC P1626 reset? If yes, see appropriate ANTI-THEFT SYSTEMS article in ACCESSORIES & EQUIPMENT. If no, go to next step.
This DTC is intermittent. If DTC additional DTCs are stored, diagnose affected DTC. If no other DTCs are is intermittent, see «DIAGNOSTIC AIDS»(/gmc/savana/i-1996-2002/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p1537-u1193) .
Repair as necessary. After repairs, go to next step.
Turn ignition off. Reconnect or reinstall components that were previously disconnected/removed. Using scan tool, clear DTCs. Check if additional DTCs are present. Diagnose affected DTCs. If no additional DTCs are present, system is okay.

DTC P1626: THEFT DETERRENT SYSTEM FUEL ENABLE CIRCUIT (5.7L "F" BODY)

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

Vehicle operation is disabled if incorrect key or starting procedure is used. Theft deterrent module enables crank circuit to starter and sends a signal to PCM if correct key is being used. If proper signal does not reach PCM fuel enable signal circuit, PCM will not pulse injectors on, disabling vehicle, even of crank circuit is by-passed. Signal should be 40-60 Hz.

DTC will set when PCM does receive the 40-60 Hz signal from the Body Control Module (BCM) and condition is present for less than one second.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(ref-132811-S27457185922002013000000) 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 DTC option and SPECIFIC DTC option, then enter this DTC. 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»(/gmc/savana/i-1996-2002/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p1537-u1193) .
If engine cranks, go to next step. If engine does not crank, diagnose theft deterrent system. See appropriate ANTI-THEFT SYSTEMS article in ACCESSORIES & EQUIPMENT.
Turn ignition off. Disconnect BCM harness connector. Turn ignition on, with engine off. Check voltage at fuel enable circuit in BCM harness connector. If voltage reading is about 5 volts, go to next step. If voltage reading is not about 5 volts, go to step 7 .
Turn ignition off. Reconnect BCM harness connector. Turn ignition on, with engine off. Using DVOM connected to ground and in Hertz (Hz) scale, backprobe BCM harness connector theft deterrent fuel enable circuit. If DVOM reads 40-61 Hz, go to next step. If DVOM does not read 40-61 Hz, go to step 8 .
Using scan tool, clear DTCs. Attempt to start engine. If engine starts and continues to run, see «DIAGNOSTIC AIDS»(/gmc/savana/i-1996-2002/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p1537-u1193) . If engine does not start or starts then dies, go to step 9 .
Check theft deterrent fuel enable circuit for open, short to ground or short to battery voltage. Repair as necessary. After repairs, go to step 12 . If circuit is okay, go to step 9 .
Check for poor terminal connections of fuel enable circuit at BCM connector. Repair as necessary. After repairs, go to step 12 . If terminal connections are okay, go to step 11 .
Check for poor terminal connections of fuel enable circuit at PCM connector. Repair as necessary. After repairs, go to step 12 . If terminal connections are okay, go to next step.
Replace PCM. Program replacement PCM using required equipment. After replacing PCM, go to step 12 .
Replace BCM. After replacing BCM, go to next step.
Using scan tool, select DTC, CLEAR INFO function. Start and warm engine to normal operating temperature. Select DTC, SPECIFIC, then enter this DTC. 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, repeat step 2 .
Using scan tool, select CAPTURE INFO, REVIEW INFO function. If any undiagnosed DTC(s) are displayed, go to applicable DTC test.

If engine starts and then stalls, indicates that portion of theft deterrent module, which generates signal to PCM is not operating or circuit between theft deterrent module and PCM is open or shorted to ground. If theft deterrent module is found to be okay, PCM may be at fault, but this not a likely condition.

DTC P1626: THEFT DETERRENT SYSTEM FUEL ENABLE CIRCUIT (5.7L "Y" BODY)

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

Vehicle operation is disabled if incorrect key or starting procedure is used. BCM confirms correct key resistor pellet and sends a password to PCM through serial data circuit. If password matches password stored in PCM, fuel will be enabled. If PCM does not receive password or BCM does not send it, PCM will set.

Conditions for setting DTC are: system has reached the fuel enable decision point and PCM is in Failed Enabled Mode due to loss of communications with BCM after system received the correct password earlier in ignition cycle.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(ref-132811-S27457185922002013000000) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Crank engine. If engine starts and runs, go to next step. If engine does not start, diagnose BCM. See appropriate BODY CONTROL MODULES article in ACCESSORIES & EQUIPMENT.
Using scan tool, check if PCM is in Vehicle Theft Deterrent (VTD) Fail Enabled Mode. If it is in VTD Fail Enabled Mode, go to next step. If it is not in VTD Fail Enabled Mode, see «DIAGNOSTIC AIDS»(/gmc/savana/i-1996-2002/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p1537-u1193) .
Using scan tool, clear PCM DTCs. Turn ignition off for one minute. Attempt to start engine. If engine starts and runs, see «DIAGNOSTIC AIDS»(/gmc/savana/i-1996-2002/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p1537-u1193) . If engine does not start and run, go to next step.
Using scan tool, read DTCs. If DTC P1626 resets, diagnose BCM. See appropriate BODY CONTROL MODULES article in ACCESSORIES & EQUIPMENT. If DTC does not set, see «DIAGNOSTIC AIDS»(/gmc/savana/i-1996-2002/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p1537-u1193) .

Most likely cause of DTC P1626 is loss of serial data communication from BCM. Check for loss of power to BCM. Check serial data circuit for open, short to ground or short to voltage.

The PCM receives analog voltage signals from various sensors. The Analog/Digital (A/D) converter changes these signals to a digital signal. This DTC will set when the A/D becomes faulty in the TC.

Record and diagnose all DTC(s). Clear DTC(s). If DTC P1627 resets, replace PCM.

This DTC indicates a fault with the PCM pull-up resistor used to revise ECT resolution throughout the entire engine operation condition. This DTC requires a cold start (IAT/ECT) to be able to detect a fault.

Record and diagnose all DTC(s). Clear DTC(s). If DTC P1628 resets, replace PCM. Program replacement PCM using required equipment.

DTC P1629: THEFT DETERRENT CRANK SIGNAL MALFUNCTION (2.2L & 2.4L "J" BODY)

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

Theft deterrent system (Passlock®) uses 4 components to determine if vehicle has Passed Theft. Lock cylinder, ignition switch, electronic Instrument Panel Cluster (IPC) and Powertrain Control Module (PCM). After system has Passed Theft, PCM will continue normal operation. If Passlock® system does not allow Passed Theft, PCM disables fuel injectors and DTC 1629 will set.

Conditions for setting DTC are: an unrecognized or no password is sent to PCM from IPC or a bad timing cycle is sent from IPC to PCM.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(ref-132811-S27457185922002013000000) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Using scan tool, check if DTC U1016 is also set. If DTC U1016 is present, diagnose DTC. If DTC U1016 is not set, go to next step.
Check for any IPC theft deterrent related DTCs. If an IPC theft deterrent DTC is set, diagnose IPC DTC. If no IPC related DTCs are set, go to next step.
Check if any Passlock® related components were replaced. If components were replaced, go to next step. If no components were replaced, go to step 6 .
Attempt to start engine. If engine starts and continues to run, go to step 7 . If engine does not start, repeat step 1 .
Replace PCM. Program replacement PCM using required equipment. After replacing PCM, go to next step.
Using scan tool, select CLEAR INFO or CLEAR DTCs function to 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 then enter this DTC. If scan tool indicates TEST RAN AND PASSED, go to next step. If scan tool does not indicate TEST RAN AND PASSED, repeat step 2 .
If any other DTCs are set, diagnose DTCs as necessary. If no other DTCs are set, no problem is indicated at this time.

An intermittent problem can be caused by a poor connection, rubbed through wire insulation or broken wire inside insulation. Password Learn Procedure.

When IPC is replaced, PCM needs to learn new password form IPC. To perform password learn procedure, attempt to start engine, then leave ignition on. THEFT SYSTEM warning indicator will flash for 10 minutes. When THEFT SYSTEM warning indicator stops flashing, start engine. Once engine is running, password is learned.

DTC P1629: THEFT DETERRENT SYSTEM CRANKING SIGNAL MALFUNCTION (3.4L "U" SERIES)

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

Conditions for setting DTC are: an attempt is made to start engine, PCM detects an incorrect signal on theft deterrent fuel enable circuit and conditions are present for longer than 2 seconds.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(ref-132811-S27457185922002013000000) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Ensure battery is fully charged. Attempt to start engine. If engine cranks, go to next step. If engine does not crank, see appropriate ANTI-THEFT SYSTEMS article in ACCESSORIES & EQUIPMENT.
Turn ignition off. Disconnect VTD module. Turn ignition on. Using DVOM, check voltage between ground circuit and fuel enable circuit at VTD module harness connector. If voltage reading is about 5 volts, go to next step. If voltage reading is not about 5 volts, go to step 6 .
Turn ignition off. Reconnect VTD module connector. Turn ignition on. Backprobe BCM harness connector, check frequency between ground and fuel enable circuit terminal at VTD module connector. If frequency is 40-60 Hz, go to next step. If frequency is not 40-60 Hz, go to step 8 .
Using scan tool, select CLEAR INFO or CLEAR DTCs function to clear DTC P1629. Attempt to start engine. If engine starts and continues to run, see «DIAGNOSTIC AIDS»(/gmc/savana/i-1996-2002/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p1537-u1193) . If engine does not start or starts but does not continue to run, go to step 7 .
Check for an open, short to ground or short to voltage in fuel enable circuit. Repair as necessary. After repairs, go to step 11 . If circuit is okay, go to next step.
Check fuel enable circuit for poor terminal connection at PCM connector. Repair as necessary. After repairs, go to step 11 . If connection is okay, go to step 9 .
Check for poor terminal connections at VTD module connector. Repair as necessary. After repairs, go to step 11 . If terminals are okay, go to step 10 .
Replace PCM. Program replacement PCM using required equipment. After replacing PCM, go to step 11 .
Replace BCM module. After replacing module, go to next step.
Using scan tool, CLEAR INFO or CLEAR DTCs function to clear DTC P1554. Using scan tool, select ENG 2 data list. Observe VTD FUEL DISABLE display. If reading indicates inactive, repair is complete. If reading does not indicate inactive, repeat step 2 .

DTC P1629: THEFT DETERRENT CRANK SIGNAL MALFUNCTION (3.8L "F", "G" & "H" BODIES)

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

Vehicle operation is disabled if incorrect key or starting procedure is used. Vehicle Theft Deterrent (VTD) module enables crank circuit to starter and sends a signal to PCM if correct key is being used. If proper signal does not reach PCM fuel enable signal circuit, PCM will not pulse injectors on, disabling vehicle, even if crank circuit is by-passed. Signal should be between 40-60 Hz and is measured using DVOM on DC scale.

DTC will set when PCM detects an incorrect signal on theft deterrent fuel enable circuit.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(ref-132811-S27457185922002013000000) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Ensure battery is fully charged. Crank engine. If engine cranks, go to next step. If engine does not crank, diagnose and repair VTD.
Turn ignition off. Disconnect VTD module connector. Turn ignition on. Using a DVOM, check voltage between TDS module harness connector ground and VTD fuel enable circuits. If voltage reading is about 5 volts, go to next step. If voltage reading is not about 5 volts, go to step 6 .
Turn ignition off. Reconnect TDS module connector. Turn ignition on. Using DVOM in Hertz (Hz) scale, check frequency between engine ground and VTD fuel enable circuit. If frequency is 40-60 Hz, go to next step. If frequency is not 40-60 Hz, go to step 8 .
Turn ignition off. Using scan tool, clear DTCs. Attempt to start engine. If engine starts and continues to run, see «DIAGNOSTIC AIDS»(/gmc/savana/i-1996-2002/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p1537-u1193) . If engine does not start, go to step 7 .
Check TDS fuel enable circuit for open, short to ground or short to battery voltage. Repair as necessary. After repairs, go to step 11 . If no problem is found, go to next step.
Check TDS fuel enable circuit for faulty connection at PCM connector. Repair as necessary. After repairs, go to step 11 . If connection is okay, go to step 9 .
Check for faulty connection at TDS module. Repair as necessary. After repairs, go to step 11 . If connection is okay, go to step 10 .
Replace PCM. Program replacement PCM using required equipment. After replacing PCM, go to step 11 .
Replace VTD module. After replacing module, go to next step.
Clear DTCs. Turn ignition on and observe VTD FUEL DISABLE scan tool display. If scan tool displays INACTIVE, repair is complete. If scan tool does not display INACTIVE, return to step 2 .

Check for faulty connections or damaged harness. Disconnect TDS module connector. Turn ignition on. Connect a DVOM between engine ground and TDS module harness connector fuel enable circuit. Observe DVOM while moving all related harness and connectors. A change in voltage display indicates fault location.

DTC P1630: THEFT DETERRENT SYSTEM PCM IN LEARN MODE (2.4L "N" BODY)

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

Vehicle Theft Deterrent (VTD) system disables engine unless the lock cylinder is correctly engaged by a mechanical key. VTD system includes lock cylinder, ignition switch, Body Function Controller (BFC) and PCM.

When starting engine, PCM looks for a password from the BFC through the Class II serial data circuit. If password is not recognized or not present, PCM will disable engine. There are 2 tamper detection modes: no password received and incorrect or disable password received (3 invalid passwords received).

DTC will set when Passlock® II password learn procedure has been interrupted or ready to learn, PCM received an incorrect password or PCM finished the 10 minute learn pending timer (ignition on for 10 minutes).

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(ref-132811-S27457185922002013000000) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Perform Password Learn Procedure. See appropriate ANTI-THEFT SYSTEMS article in ACCESSORIES & EQUIPMENT. Attempt to start engine. If engine starts and continues to run, go to step 5 . If engine does not start or starts and then stalls, go to next step.
Check if VTD components has been recently replaced. If components has been replaced, repeat step 2 . If components has not been replaced recently, go to next step.
Replace PCM. Program replacement PCM using required equipment. After replacing PCM, go to next step.
Using scan tool, clear DTCs. Warm engine to normal operating temperature. Operate vehicle within the conditions for setting this DTC. If scan tool indicates that this DTC ran and passed, go to next step. If scan tool does not indicate that this DTC ran and passed, repeat step 2 .
Check if additional DTC are set. Diagnose affected DTCs. If no other DTCs are set, system is okay.

Attempting to start vehicle by by-passing the theft deterrent system or substituting parts without performing the password learn procedure may set DTC. If no password is received, DTC P1610, P1626 and P1631 may set. PCM must be reflashed to allow new password to be learned if BFC is replaced. Turn ignition off for at least 30 seconds then on for PCM to learn the new BFC password.

An intermittent may be caused by poor connection, rubbed-through wire insulation or a broken wire inside insulation.

DTC P1630: THEFT DETERRENT SYSTEM PCM IN LEARN MODE (3.1L "N" BODY)

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

DTC will set when Passlock® password learn procedure has been interrupted or ready to learn.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(ref-132811-S27457185922002013000000) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Perform Password Learn Procedure. See appropriate ANTI-THEFT SYSTEMS article in ACCESSORIES & EQUIPMENT. Attempt to start engine. If engine starts and continues to run, go to step 5 . If engine does not start or starts and then stalls, go to next step.
Check if VTD components has been recently replaced. If components has been replaced, repeat step 2 . If components has not been replaced recently, go to next step.
Replace PCM. Program replacement PCM using required equipment. After replacing PCM, go to next step.
Using scan tool, clear DTCs. Warm engine to normal operating temperature. Operate vehicle within the conditions for setting this DTC. If scan tool indicates that this DTC ran and passed, go to next step. If scan tool does not indicate that this DTC ran and passed, repeat step 2 .
Check if additional DTC are set. Diagnose affected DTCs. If no other DTCs are set, system is okay.

An intermittent may be caused by poor connection, rubbed-through wire insulation or a broken wire inside insulation.

DTC P1630: THEFT DETERRENT SYSTEM PCM IN LEARN MODE (3.1L "W" BODY)

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

If the BCM has been replaced, the password must be relearned using special equipment. If PCM is replaced, the replacement PCM should relearn the password within a few seconds after ignition is turned on. Engine will start and continue to run with DTC P1630 set. See appropriate ANTI-THEFT SYSTEMS article in ACCESSORIES & EQUIPMENT.

Conditions for setting DTC are: PASS-Key® III system has allowed fuel delivery or when PCM is theft deterrent password learn mode.

A new PCM will be in a functional state to learn the password from the BCM. If BCM is replaced, PCM must be placed in password learning mode to relearn new password. Once learned, the password becomes permanent information that remains with vehicle. The loss of PCM battery or ignition voltage will not affect the programmed information.

DTC P1630: THEFT DETERRENT PCM IN LEARN MODE (3.4L "N" BODY)

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

The vehicle theft deterrent system is designed to prevent vehicle theft by disabling the engine unless the lock cylinder is correctly engaged by mechanical key. Theft deterrent system uses 4 components for theft detection: lock cylinder, ignition switch, Body Function Controller (BFC) and PCM.

When engine is started, PCM looks for a password from the BFC through the Class II serial data circuit. If password is not recognized or not present, PCM will disable engine. The 2 modes of tamper detection are, no password received or incorrect or disable password received (greater than 3 invalid passwords received). The THEFT SYSTEM light will flash or illuminate.

After the vehicle has passed theft detection, PCM will continue normal engine operation. DTC will set when Passlock® password learn procedure has been interrupted or ready to learn.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(ref-132811-S27457185922002013000000) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Perform password relearn procedure. See appropriate ANTI-THEFT SYSTEMS article in ACCESSORIES & EQUIPMENT. After performing password relearn procedure, attempt to start engine. If engine starts and continues to run, go to step 5 . If engine does not start or starts and dies, go to next step.
Check if Vehicle Theft Deterrent (VTD) component has been recently replaced. If VTD component has been replaced, repeat step 2 . If VTD component has not been replaced, go to next step.
Replace PCM. Program replacement PCM using required equipment. After replacing PCM, go to next step.
Using scan tool, clear DTCs. Warm engine to normal operating temperature. Operate vehicle within the conditions for setting this DTC. If scan tool indicates that this DTC ran and passed, go to next step. If scan tool does not indicate that this DTC ran and passed, repeat step 2 .
Using scan tool, check for additional DTCs. Diagnose affected DTCs. If no other DTCs are set, system is okay.

Attempting to start vehicle by by-passing the theft deterrent system or substituting parts without performing password relearn procedure may set DTC P1631. If no password is received, a DTC P1610, P1626 and P1631 may set.

An intermittent may be caused by a poor connection, rubbed-through insulation or a wire broken inside the insulation. If BFC is replaced, PCM must be reflashed to allow new password to be learned. Ignition must be turned off for at least 30 seconds then turned on for the PCM to learn the new BFC password.

DTC P1630: THEFT DETERRENT SYSTEM PCM IN LEARN MODE (3.5L "W" BODY)

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

The Vehicle Theft Deterrent (VTD) system is incorporated within the BCM. If the BCM has been replaced, the password must be relearned using special equipment. If PCM is replaced, the replacement PCM should relearn the password within a few seconds after ignition is turned on. Engine will start and continue to run with DTC P1630 set. See appropriate ANTI-THEFT SYSTEMS article in ACCESSORIES & EQUIPMENT.

DTC will set when VTD system has allowed fuel delivery, PCM is theft deterrent password learn mode and PCM remains in theft deterrent password for greater than 2 seconds.

DTC P1630: THEFT DETERRENT SYSTEM PCM IN LEARN MODE (3.8L "C" & "W" BODIES)

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

Conditions for setting DTC are: Vehicle Theft Deterrent (VTD) system has allowed fuel delivery, PCM is theft deterrent password learn mode and condition is present for greater than 2 seconds.

DTC P1630: THEFT DETERRENT LEARN MODE ACTIVE (4.6L "E" & "K" BODIES)

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

This test checks for the enable password learning flag, indicating that PCM is in learn password mode. This mode allows PCM to learn the password from the VTD controller at assembly or when being serviced. The password needs to be learned whenever PCM or IPC is replaced.

The PCM in learn mode is a DTC for the vehicle at the assembly plant or repair facility personnel to indicate that the learn mode is enabled, meaning that the PCM is now ready to learn a new password.

DTC P1630: THEFT DETERRENT SYSTEM VCM IN LEARN MODE (5.0L & 5.7L "C" & "K" SERIES)

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

This diagnostic checks for enable password learning flag indicating VCM is in learn password mode. This mode allows VCM to learn password from Vehicle Theft Deterrent (VTD) system at assembly or when being serviced. Password has to be learned whenever VTD or VCM are replaced.

DTC will set when the enable learning flag is set.

Perform On-Board Diagnostic (OBD) system check. See ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, diagnose BCM. See appropriate BODY CONTROL MODULE article in ACCESSORIES & EQUIPMENT.

DTC P1630: THEFT DETERRENT SYSTEM PCM IN LEARN MODE (5.7L "Y" BODY)

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

This diagnostic checks for enable password learning flag, indicating PCM is in learn password mode. This mode allows PCM to learn password from BCM at assembly or when being serviced. Password has to be learned whenever BCM or PCM are replaced or ignition key has invalid resistor pellet.

DTC will also set when BCM is not sending a valid password or not sending a password at all.

Perform On-Board Diagnostic (OBD) system check. See ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. If DTC P1630 is still present after performing OBD system check, diagnose BCM. See appropriate BODY CONTROL MODULE article in ACCESSORIES & EQUIPMENT.

DTC P1631: THEFT DETERRENT SYSTEM PASSWORD INCORRECT (2.2L "S" SERIES & 2.4L "N" BODY)

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

When starting engine, PCM looks for a password from the BFC or TBC through the Class II serial data circuit. If password is not recognized or not present, PCM will disable engine. There are 2 tamper detection modes: no password received and incorrect or disable password received (3 invalid passwords received).

DTC will set when an unrecognized or incorrect password sent to PCM from BFC or TBC.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(ref-132811-S27457185922002013000000) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Using scan tool, display data list for BFC or TBC. If scan tool indicates that Passlock® data is valid, go to next step. If scan tool does not indicate that Passlock® data is valid, go to step 4 .
Perform Password Learn Procedure. See appropriate ANTI-THEFT SYSTEMS article in ACCESSORIES & EQUIPMENT. Attempt to start engine. If engine starts and continues to run, go to step 7 . If engine does not start or starts and then stalls, go to step 6 .
Check if any theft deterrent related DTCs are set. Diagnose affected DTCs. If theft deterrent related DTCs are not set, go to next step.
Diagnose theft deterrent system. See appropriate ANTI-THEFT SYSTEMS article in ACCESSORIES & EQUIPMENT.
Replace PCM. Program replacement PCM using required equipment. After replacing PCM, go to next step.
Using scan tool, clear DTCs. Warm engine to normal operating temperature. Operate vehicle within the conditions for setting this DTC. If scan tool indicates that this DTC ran and passed, go to next step. If scan tool does not indicate that this DTC ran and passed, repeat step 2 .
Check if additional DTC are set. Diagnose affected DTCs. If no other DTCs are set, system is okay.

Attempting to start vehicle by by-passing the theft deterrent system or substituting parts without performing the password learn procedure may set DTC. If no password is received, DTC P1631 and P1632 may set. PCM must be reflashed to allow new password to be learned if BFC or TBC is replaced. Turn ignition off for at least 30 seconds then on for PCM to learn the new password.

An intermittent may be caused by poor connection, rubbed-through wire insulation or a broken wire inside insulation.

DTC P1631: THEFT DETERRENT SYSTEM PASSWORD INCORRECT (3.1L "N" BODY)

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

DTC will set when an unrecognized or no password is sent to PCM from the BFC.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(ref-132811-S27457185922002013000000) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Using scan tool, display DATA LIST for BFC. If scan tool indicates that Passlock® data is valid, go to next step. If scan tool does not indicate that Passlock® is not valid, go to step 4 .
Perform Password Learn Procedure. See appropriate ANTI-THEFT SYSTEMS article in ACCESSORIES & EQUIPMENT. Attempt to start engine. If engine starts and continues to run, go to step 7 . If engine does not start or starts and then stalls, go to step 6 .
Check if VTD related DTCs are set. Diagnose affected DTCs. If no other DTCs are set, go to next step.
Check if VTD components has been recently replaced. If components has been replaced, repeat step 2 . If components has not been replaced recently, go to step 7 .
Replace PCM. Program replacement PCM using required equipment. After replacing PCM, go to next step.
Using scan tool, clear DTCs. Warm engine to normal operating temperature. Operate vehicle within the conditions for setting this DTC. If scan tool indicates that this DTC ran and passed, go to next step. If scan tool does not indicate that this DTC ran and passed, repeat step 2 .
Check if additional DTC are set. Diagnose affected DTCs. If no other DTCs are set, system is okay.

Attempting to start vehicle by by-passing the theft deterrent system or substituting parts without performing the password learn procedure may set DTC. If no password is received, DTC P1610, P1626 and P1631 may set. PCM must be reflashed to allow new password to be learned if BFC or TBS is replaced. Turn ignition off for at least 30 seconds then on for PCM to learn the new BFC password.

An intermittent may be caused by poor connection, rubbed-through wire insulation or a broken wire inside insulation.

DTC P1631: THEFT DETERRENT SYSTEM PASSWORD INCORRECT (3.1L "W" BODY)

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

PCM controls fuel injector and starter operation based on Vehicle Theft Deterrent (VTD) password from the BCM. When ignition is first turned on, BCM sends a programmed password to the PCM. PCM acknowledges the password and responds to the BCM that normal fuel injector operation will continue. If PCM detects an incorrect password (VTD system failure or attempted vehicle theft), DTC P1631 will set. The engine will not start as long as the condition is present.

DTC will set when PCM is detecting an incorrect vehicle theft deterrent password from the VTD system.

Perform On-Board Diagnostic (OBD) system check. See ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, perform theft learn procedure. See appropriate ANTI-THEFT SYSTEMS article in ACCESSORIES & EQUIPMENT.

DTC P1631 indicates that the vehicle theft deterrent password that the PCM has learned does not agree with password being received from the VTD system. This condition can occur if an incorrect key is being used when attempting to start vehicle or if BCM has been replaced and the PCM's password learn function has not been enabled.

If BCM has been replaced, the password must be relearned using special equipment.

DTC P1631: THEFT DETERRENT SYSTEM PASSWORD INCORRECT (3.4L "N" BODY)

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

After the vehicle has passed theft detection, PCM will continue normal engine operation. DTC will set when an unrecognized or no password is sent to the PCM from the BFC.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(ref-132811-S27457185922002013000000) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Using scan tool, display data list for BFC. If scan tool indicates that the Passlock® data is valid, go to next step. If scan tool does not indicate that the Passlock® data is valid, go to step 4 .
Perform Password Learn Procedure. See appropriate ANTI-THEFT SYSTEMS article in ACCESSORIES & EQUIPMENT. If engine starts and continues to run, go to step 7 . If engine does not start or starts and dies, go to step 6 .
Check if any Passlock® theft deterrent DTC are set. If theft deterrent related DTCs are set, diagnose affected DTCs. See appropriate ANTI-THEFT SYSTEMS article in ACCESSORIES & EQUIPMENT. If theft deterrent DTCs are not set, go to next step.
Diagnose anti-theft system. See appropriate ANTI-THEFT SYSTEMS article in ACCESSORIES & EQUIPMENT.
Replace PCM. Program replacement PCM using required equipment. After replacing PCM, go to next step.
Using scan tool, clear DTCs. Warm engine to normal operating temperature. Operate vehicle within the conditions for setting this DTC. If scan tool indicates that this DTC ran and passed, go to next step. If scan tool does not indicate that this DTC ran and passed, repeat step 2 .
Using scan tool, check for additional DTCs. Diagnose affected DTCs. If no other DTCs are set, system is okay.

An intermittent may be caused by a poor connection, rubbed-through insulation or a wire broken inside the insulation. If serial data loss occurred after a good theft password has been received, PCM must be reprogrammed and password learn and crankshaft position variation learn procedures must be completed to allow the theft deterrent system to operate properly.

DTC P1631: THEFT DETERRENT SYSTEM PASSWORD INCORRECT (3.5L "W" BODY)

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

PCM controls fuel injector and starter operation based on Vehicle Theft Deterrent (VTD) password from the BCM. When ignition is first turned on, BCM sends a programmed password to the PCM. PCM acknowledges the password and responds to the BCM that normal fuel injector operation will continue. If PCM detects an incorrect password (VTD system failure or attempted vehicle theft), DTC will set. The engine will not start as long as the condition is present.

Conditions for setting DTC are: PCM is detecting an incorrect vehicle theft deterrent password from VTD system, VTD system allowed fuel delivery and if these conditions are present for greater than one second.

Perform On-Board Diagnostic (OBD) system check. See ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, perform password learn procedure. See appropriate ANTI-THEFT SYSTEMS article in ACCESSORIES & EQUIPMENT.

If BCM has been replaced, the password must be relearned using special equipment.

DTC P1631: THEFT DETERRENT SYSTEM PASSWORD INCORRECT (3.8L "C" & "W" BODIES)

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

PCM controls fuel injector and starter operation based on vehicle theft deterrent password from the BCM. When ignition is first turned on, BCM sends a programmed password to the PCM. PCM acknowledges the password and responds to the BCM that normal fuel injector operation will continue. If PCM detects an incorrect password (Vehicle Theft Deterrent system failure or attempted vehicle theft), DTC P1631 will set. The engine will not start as long as the condition is present.

Conditions for setting DTC are: PCM is detecting an incorrect vehicle theft deterrent password from Vehicle Theft Deterrent (VTD) system, VTD system allowed fuel delivery and conditions are present for greater than 2 seconds.

Perform On-Board Diagnostic (OBD) system check. See ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, perform password learn procedure. See appropriate ANTI-THEFT SYSTEMS article in ACCESSORIES & EQUIPMENT.

If BCM has been replaced, the password must be relearned using special equipment.

DTC P1631: THEFT DETERRENT SYSTEM PASSWORD INCORRECT (4.3L "C", "K", "L", "M", "S" & "T" SERIES)

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

When VCM receives a invalid password or no password before the fuel disable decision point, VCM disables fuel delivery. Fuel disable decision point occurs at about 300 RPM during engine crank mode.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(ref-132811-S27457185922002013000000) 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 VTD Passlock® DTC. If any related DTCs are set, diagnose anti-theft system. See appropriate ANTI-THEFT SYSTEMS article in ACCESSORIES & EQUIPMENT. If no related DTCs are set, go to next step.
Perform Passlock® reprogramming procedure. See appropriate ANTI-THEFT SYSTEMS article in ACCESSORIES & EQUIPMENT. If password was successfully learned, go to next step. If password was not learned, see appropriate ANTI-THEFT SYSTEMS article in ACCESSORIES & EQUIPMENT
Using scan tool, clear all DTCs. Turn ignition off for 30 seconds, then attempt to start engine. If engine starts and runs, system is okay. If engine does not start, repeat step 2 .

DTC P1631: THEFT DETERRENT START ENABLE SIGNAL NOT CORRECT (4.6L "E" & "K" BODIES)

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

This test checks for mismatched passwords between the IPC and PCM. Whenever the IPC or PCM are replaced, a theft learn procedure must be followed in order for the new password to be learned.

Perform On-Board Diagnostic (OBD) system check. See ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, perform theft learn procedure. See appropriate ANTI-THEFT SYSTEMS article in ACCESSORIES & EQUIPMENT.

DTC P1631: THEFT DETERRENT SYSTEM PASSWORD INCORRECT (4.8L, 5.3L & 6.0L "C" & "K" SERIES)

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

This test checks for mismatched passwords between the BCM and PCM. Whenever BCM or PCM is replaced, follow theft learn procedures for system to learn new password. DTC will set when PCM detects a wrong password from the BCM, fuel disable lockout is set, system has received an incorrect fuel continue password, faulty ignition switch or BCM was replaced.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(ref-132811-S27457185922002013000000) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Using scan tool, check if any BCM related DTCs are set. If BCM related DTCs are set, diagnose DTCs. Perform theft learn procedure. If using Tech 2 scan tool, go to step 4 . If not using Tech 2 scan tool, go to next step.
Turn ignition on, with engine off for 11 minutes. Turn ignition off for 30 seconds. Repeat turning on ignition for 11 minutes, and turning it off for 30 seconds 2 times. Turn ignition on, with engine off and wait 30 seconds. Attempt to start engine. If engine starts and operates normally, go to step 5 . If engine does not start or operate normally, go to step 6 .
Using scan tool, enter SERVICE PROGRAMMING SYSTEM. Enter vehicle information. Select REQUEST INFO. Select DONE and follow instructions on VEHICLE SET-UP screen. Disconnect scan tool from vehicle. Connect scan tool to Techline terminal. At Techline terminal select SERVICE PROGRAMMING SYSTEM (STS) and select terminal to Tech 2 programming method. Select DONE and follow instructions on screen. Select VEHICLE THEFT RELEARN option. Select PROGRAM at summary screen. The terminal will download information to scan tool. Reconnect scan tool to vehicle. Select SERVICE PROGRAMMING on scan tool menu. Follow instructions. Press THEFT RELEARN key on scan tool. Follow instructions on remaining screens. PCM and BCM will be prepared for relearn. A security timer will be on for about 11 minutes. When BCM and PCM are prepared to relearn, turn ignition off for 30 seconds and attempt to start engine. If engine starts and operates normally, go to next step. If engine does not start or operate normally, go to step 6 .
Using scan tool, clear PCM DTCs. Turn ignition off for 30 seconds. Attempt to start engine. If engine starts and operates normally, system is okay. If engine does not start and run, go to next step.
Using scan tool, read DTCs. If DTC P1626 or P1631 is set, diagnose affected DTC(s). If DTC P1626 or P1631 is not set, return to step 2 .

DTC P1631: THEFT DETERRENT SYSTEM PASSWORD INCORRECT (5.0L & 5.7L "C" & "K" SERIES)

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

When VCM receives a invalid password or no password before the fuel disable decision point, VCM disables fuel delivery. Fuel disable decision point occurs at about 300 RPM during engine crank mode.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(ref-132811-S27457185922002013000000) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Unless sent here after replacing VCM, check for any BCM DTCs being set. If a BCM DTC is set, see appropriate BODY CONTROL MODULES article in ACCESSORIES & EQUIPMENT. If T-50/T-60 scan tool is being used, go to step 5 . If T-50/T-60 scan tool is not being used, go to next step.
If Tech 2 scan tool is being used, go to step 6 . If Tech 2 scan tool is not being used, go to next step. NOTE: While VCM is in Auto Learn Procedure, battery voltage must be maintained at all time. This procedure must be followed exactly or procedure will have to be repeated from beginning. Performing following procedures will set DTC P1630. Turn ignition off for 30 seconds, then turn ignition on. DTC P1630 should clear. If DTC does not clear, diagnose DTC P1630.
Turn ignition on, with engine off for 11 minutes. Turn ignition off for 30 seconds. Repeat turning on ignition for 11 minutes, and turning it off for 30 seconds 2 times. Turn ignition on, with engine off and wait 30 seconds. Attempt to start engine. If engine starts and operates normally, go to step 7 . If engine does not start or operate normally, go to step 8 .
Using T-50/T60 scan tool, enter SERVICE PROGRAMMING SYSTEM. Select TERMINAL-TO-VEHICLE PROGRAMMING. Select DONE and follow instructions on VEHICLE SET-UP screen. Select VEHICLE THEFT RELEARN. Follow instructions on remaining screens. PCM and BCM will be prepared for relearn. A security timer will be on for about 11 minutes or DTC P1630 sets. Keep terminal connected to vehicle during 11 minute period. When BCM and VCM are prepared to relearn, turn ignition off for 30 seconds and attempt to start engine. If engine starts and operates normally, go to step 7 . If engine does not start or operate normally, go to step 8 .
Using Tech 2 scan tool, enter SERVICE PROGRAMMING SYSTEM. After keying vehicle information, select REQUEST INFO key. Select DONE and follow instructions on VEHICLE SET-UP screen. Disconnect scan tool from vehicle and connect it to Techline terminal. At Techline terminal, select SERVICE PROGRAMMING SYSTEM. Select TERMINAL-TO-TECH 2 PROGRAMMING. Select DONE. Follow instructions on remaining screens. Select VEHICLE THEFT RELEARN. Select PROGRAM. Return scan tool to vehicle and connect to DLC. Select SERVICE PROGRAMMING SYSTEM. After keying vehicle information, select REQUEST INFO key. Select THEFT RELEARN. Follow instructions on remaining screens. PCM and BCM will be prepared for relearn. A security timer will be on for about 11 minutes or DTC P1630 sets. Keep terminal connected to vehicle during 11 minute period. When BCM and PCM are prepared to relearn, turn ignition off for 30 seconds and attempt to start engine. If engine starts and operates normally, go to next step. If engine does not start or operate normally, go to step 8 .
Using scan tool, clear VCM DTCs. Turn ignition off for 30 seconds. Attempt to start engine. If engine starts and operates normally, system is okay. If engine does not start and run, go to next step.
Using scan tool, read DTCs. If DTC P1626 or P1630 is set, diagnose affected DTC(s). If DTC P1631 resets, return to step 2 .

DTC P1631: THEFT DETERRENT SYSTEM PASSWORD INCORRECT (5.7L "Y" BODY)

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

This diagnostic checks for mismatched passwords between BCM and PCM. Password has to be learned whenever BCM or PCM are replaced.

Conditions for setting DTC are: PCM detects incorrect password from BCM, fuel disable lock-out set, incorrect fuel continue password is received, invalid ignition key or faulty ignition switch or BCM was replaced.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(ref-132811-S27457185922002013000000) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Unless sent here after replacing PCM, check for any BCM DTCs being set. If a BCM DTC is set, diagnose DTC. See appropriate BODY CONTROL MODULES article in ACCESSORIES & EQUIPMENT. If T-50/T-60 scan tool is being used, go to step 5 . If T-50/T-60 scan tool is not being used, go to next step.
If Tech 2 scan tool is being used, go to step 6 . If Tech 2 scan tool is not being used, go to next step. NOTE: While PCM is in Auto Learn Procedure, battery voltage must be maintained at all time. This procedure must be followed exactly or procedure will have to be repeated from beginning. Performing following procedures will set DTC P1630. Turn ignition off for 30 seconds, then turn ignition DTC P1630 should clear. If DTC P1630 does not clear, diagnose DTC P1630.
Turn ignition on, with engine off for 11 minutes. Turn ignition off for 30 seconds. Repeat turning on ignition for 11 minutes, and turning it off for 30 seconds 2 times. Turn ignition on, with engine off and wait 30 seconds. Attempt to start engine. If engine starts and operates normally, go to step 7 . If engine does not start or operate normally, go to step 8 .
Using T-50/T60 scan tool, enter SERVICE PROGRAMMING SYSTEM. Select TERMINAL-TO-VEHICLE PROGRAMMING. Select DONE and follow instructions on VEHICLE SET-UP screen. Select VEHICLE THEFT RELEARN. Follow instructions on remaining screens. PCM and BCM will be prepared for relearn. A security timer will be on for about 11 minutes or DTC P1630 sets. Keep terminal connected to vehicle during 11 minute period. When BCM and PCM are prepared to relearn, turn ignition off for 30 seconds and attempt to start engine. If engine starts and operates normally, go to step 7 . If engine does not start or operate normally, go to step 8 .
Using Tech 2 scan tool, enter SERVICE PROGRAMMING SYSTEM. After keying vehicle information, select REQUEST INFO key. Select DONE and follow instructions on VEHICLE SET-UP screen. Disconnect scan tool from vehicle and connect it to Techline terminal. At Techline terminal, select SERVICE PROGRAMMING SYSTEM. Select TERMINAL-TO-TECH 2 PROGRAMMING. Select DONE. Follow instructions on remaining screens. Select VEHICLE THEFT RELEARN. Select PROGRAM. Return scan tool to vehicle and connect to DLC. Select SERVICE PROGRAMMING SYSTEM. After keying vehicle information, select REQUEST INFO key. Select THEFT RELEARN. Follow instructions on remaining screens. PCM and BCM will be prepared for relearn. A security timer will be on for about 11 minutes or DTC P1630 sets. Keep terminal connected to vehicle during 11 minute period. When BCM and PCM are prepared to relearn, turn ignition off for 30 seconds and attempt to start engine. If engine starts and operates normally, go to next step. If engine does not start or operate normally, go to step 8 .
Using scan tool, clear PCM DTCs. Turn ignition off for 30 seconds. Attempt to start engine. If engine starts and operates normally, system is okay. If engine does not start and run, go to next step.
Using scan tool, read DTCs. If DTC P1626, P1630 or P1631 is set, diagnose affected DTC(s). If DTC P1631 resets, return to step 2 .

DTC P1632: THEFT DETERRENT SYSTEM FUEL DISABLED (2.2L "S" SERIES & 2.4L "N" BODY)

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

DTC will set when an unrecognized or incorrect password sent to PCM from BFC or TBC or an undecided password sent from BFC or TBC.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(ref-132811-S27457185922002013000000) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Using scan tool, check if DTCs P1626, P1630 or P1631 is also set. Diagnose affected DTC(s). If DTCs are not set, go to next step.
Perform Password Learn Procedure. See appropriate ANTI-THEFT SYSTEMS article in ACCESSORIES & EQUIPMENT. Attempt to start engine. If engine starts and continues to run, go to step 8 . If engine does not start or starts and then stalls, go to next step.
Using scan tool, display data list for BFC or TBC (trucks). If scan tool indicates that Passlock® data is valid, go to next step. If scan tool does not indicate that Passlock® data is valid, go to step 6 .
Replace PCM. Program replacement PCM using required equipment. After replacing PCM, go to step 8 .
Check if there are any theft deterrent related DTCs set. Diagnose affected DTCs. If no theft deterrent related DTCs are set, go to next step.
Diagnose theft deterrent system. See appropriate ANTI-THEFT SYSTEMS article in ACCESSORIES & EQUIPMENT. After repairs, go to next step.
Using scan tool, clear DTCs. Warm engine to normal operating temperature. Operate vehicle within the conditions for setting this DTC. If scan tool indicates that this DTC ran and passed, go to next step. If scan tool does not indicate that this DTC ran and passed, repeat step 2 .
Check if additional DTC are set. Diagnose affected DTCs. If no other DTCs are set, system is okay.

Attempting to start vehicle by by-passing the theft deterrent system or substituting parts without performing the password learn procedure may set DTC. If no password is received, DTC P1610 and P1632 may set. PCM must be reflashed to allow new password to be learned if BFC or TBC is replaced. Turn ignition off for at least 30 seconds then on for PCM to learn the new password.

An intermittent may be caused by poor connection, rubbed-through wire insulation or a broken wire inside insulation.

DTC P1632: THEFT DETERRENT FUEL DISABLE SIGNAL RECEIVED (4.6L "E" & "K" BODIES)

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

This DTC sets when PCM has received fuel disabled or fuel undecided passwords from the Vehicle Theft Deterrent (VTD) controller. It is set as a tool to indicate that the VTD is not allowing fuel due to possible theft attempt or a worn or incorrect ignition key.

If DTC is set, it means that IPC has received incorrect resistance value or an unrecognizable resistance value from ignition key. Check ignition key to ensure it is the correct key for vehicle and that it is clean and dry. Wait 10 minutes between attempts to clean and retry key. DTC will set when a theft is attempted.

DTC P1633: IGNITION 0 SWITCH CIRCUIT (4.0L "G" BODY & 4.6L "E" & "K" BODIES)

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

PCM is powered by 5 power feeds. Two of these feed are from the battery, the other 3 are from the ignition switch and are called Ignition 1, Ignition 0 and Ignition Supplement. The ignition feeds are powered any time the key is in the CRANK, RUN or ACC positions. This test is used to monitor the ignition supplement voltage received at the PCM connector C2, terminal No. 37. PCM monitors this voltage and if voltage drops too low for one second, DTC will set.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(ref-132811-S27457185922002013000000) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Using scan tool, check if DTC P1634 is also present. If DTC P1634 is also present, diagnose this DTC first. If DTC P1634 is not present, go to next step.
Store fluid life index as indicated on scan tool. Turn ignition off and wait 30 seconds, then disconnect PCM harness connector C2. Turn ignition on. Using DVOM, check voltage between ground and ignition feed circuit at PCM harness connector C2, terminal No. 37. Using scan tool, note and write down IGNITION 1 voltage reading. If DVOM and scan tool voltage readings are within.5 volt of each other, go to next step. If DVOM and scan tool voltage readings are not within.5 volt of each other, go to step 5 .
Turn ignition off. Reconnect PCM harness connector C2. Turn ignition on. Using scan tool, clear DTC. Start and idle engine. After 10 seconds in DTC INFO mode, select FAIL THIS IGN. If DTC failed in this ignition cycle, go to step 6 . If DTC did not fail in this ignition cycle, fault is not present. See «DIAGNOSTIC AIDS»(/gmc/savana/i-1996-2002/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p1537-u1193) .
Repair open in ignition feed circuit between PCM harness connector and splice.
Check terminal contact at PCM harness connector C2, terminal No. 37. Repair as necessary. If terminal contact is okay, go to next step.
Replace PCM. Program replacement PCM using required equipment.

If ignition supplement to the PCM is lost, the engine will still run, but some outputs may not function. If Ignition 1 voltage is lost or drops to less than 5.5 volts, engine will not run and DTC should set.

If this DTC is intermittent, check terminal contact at PCM and condition of splice for an intermittent open circuit.

DTC P1634: IGNITION 1 SWITCH CIRCUIT (4.0L "G" BODY)

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

PCM is powered by 5 power feeds. Two of these feed are from the battery, the other 3 are from the ignition switch and are called Ignition 1, Ignition 0 and Ignition Supplement. The ignition feeds are powered any time the key is in the CRANK, RUN or ACC positions. This test is used to monitor the voltages received by the PCM at PCM harness connector terminals No. 18 and 19.

When engine is running, PCM will compare the Ignition 1 voltage it receives at terminal No. 19 to the Ignition 0 voltage it receives at terminal No. 18. If voltage difference is greater than 2 volts for 5 seconds, DTC will set.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(ref-132811-S27457185922002013000000) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Using scan tool, check if DTC P0560 is also present. If DTC P0560 is also present, diagnose this DTC first. If DTC P0560 is not present, go to next step.
Note both the IGNITION 0 and IGNITION 1 displays on scan tool. Compare both voltage readings. If readings are within 1.5 volts of each other, go to next step. If readings are not within 1.5 volts of each other, go to step 5 .
Clear DTC using scan tool. Start and idle engine. After 10 seconds in DTC INFO mode, select FAIL THIS IGN. If DTC failed this ignition cycle, go to step 6 . If DTC did not fail this ignition cycle, fault is not present. See «DIAGNOSTIC AIDS»(/gmc/savana/i-1996-2002/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p1537-u1193) .
Check for open circuit or poor splice connection on circuit that has low voltage. Replace as necessary. If circuit is okay, fault is not present. «DIAGNOSTIC AIDS»(/gmc/savana/i-1996-2002/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p1537-u1193) .
Check terminal contact at PCM harness connector C1 terminals No. 18 and 19. Repair as necessary. If terminal contacts are okay, go to next step.
Replace PCM. Program replacement PCM using required equipment.

If Ignition 0 to the PCM is lost, the engine will still run, but some outputs may not function. If Ignition 1 voltage is lost or drops to less than 5.5 volts, engine will not run and DTC should set.

If this DTC is intermittent, check terminal contact at PCM and condition of splice for an intermittent open circuit.

DTC P1634: IGNITION 1 SWITCH CIRCUIT (4.6L "E" & "K" BODIES)

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

PCM is powered with 5 power feeds. Two of these feeds are from the battery, the other 3 are from the ignition switch and are called ignition 1, ignition supplement and ignition 0. Ignition 1 and ignition supplement are powered any time the key in the CRANK, RUN or ACC positions. Ignition 0 is powered in all key positions except LOCK and CRANK.

This test is used to monitor the voltages received by the PCM at harness connector C1 terminals No. 18 and 19. When engine is running, PCM will compare Ignition 1 voltage it receives at PCM harness connector C1 terminal No. 19 to the Ignition 0 voltage it receives at PCM harness connector C1 terminal No. 18. If Ignition 1 and Ignition 0 voltage difference is greater than 2 volts for 5 seconds, DTC will set.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(ref-132811-S27457185922002013000000) 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 DTC P0560 is also present. If DTC P0560 is present, diagnose DTC first. If DTC P0560 is not present, go to next step.
Using scan tool in ENGINE 1 mode, note both IGNITION 0 and IGNITION 1 displays. Compare both readings. If voltage difference is less than 1.5 volts within each other, go to next step. If voltage difference is greater than 1.5 volts within each other, go to step 5 .
Clear DTC using scan tool. Start and idle engine. After 10 seconds in DTC INFO mode, select FAIL THIS IGN. If scan tool indicates that this DTC failed this ignition cycle, go to step 12 . If scan tool does not indicate that this DTC failed this ignition cycle, fault is not present. See «DIAGNOSTIC AIDS»(/gmc/savana/i-1996-2002/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p1537-u1193) .
If Ignition 0 voltage was lower than Ignition 1 voltage, go to next step. If Ignition 0 voltage was greater than Ignition 1 voltage, go to step 7 .
Check Ignition 0 fuse (IGN 0-ENG). If fuse is faulty, go to step 10 . If fuse is okay, go to step 9 .
Check Ignition 1 fuse (PCM-IGN). If fuse is faulty, go to next step. If fuse is okay, go to step 11 .
Repair short to ground in Ignition 1 feed circuit between PCM and engine compartment fuse/relay block. Replace fuse.
Repair open/high resistance or poor terminal contact in Ignition 0 feed circuit between PCM and engine compartment fuse/relay block.
Repair short to ground in Ignition 0 feed circuit between PCM and engine compartment fuse/relay block. Replace fuse.
Repair open/high resistance or poor terminal contact at Ignition 1 feed circuit between PCM and engine compartment fuse/relay block.
Check terminal contact at PCM harness connector C1 terminals No. 18 and 19. Repair as necessary. If terminals are okay, go to next step.
Replace PCM. Program replacement PCM using required equipment.

If Ignition 0 to PCM is lost, vehicle will still run but some outputs may not function. If Ignition 1 voltage is lost or drops to less than 5.5 volt, vehicle will not run and DTC should set. If DTC is intermittent, check terminal contact at PCM and condition of ignition feed circuit splice for an intermittent open.

The 5-volt reference circuit provides a signal voltage to the linear EGR, MAP sensor and TP sensor. The return line is grounded through the PCM. This DTC detects a short to ground in any of the three 5-volt reference circuits or inside the PCM.

DTC will set if the 5-volt reference signal is less than 3.5 volts or greater than 5.5 volts. This voltage is monitored internally by the PCM. The 5-volt reference is monitored whenever the ignition is on.

Install scan tool. Turn ignition on. Using scan tool, monitor TP sensor, MAP and EGR voltages. If they all read less than.24 volt, go to next step. If MAP voltage is greater than 5.1 volts, go to step 4 . If MAP voltage is not greater than 5.1 volts, problem is intermittent. See «DIAGNOSTIC AIDS»(/gmc/savana/i-1996-2002/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p1537-u1193) .
Turn ignition off. Disconnect PCM harness connector J2. Using a test light connect to battery voltage, probe PCM harness connector terminals J2B04 and J2B05. If test light illuminates, go to next step. If test light does not illuminate, replace PCM.
Disconnect MAP, EGR, and TP sensor one at a time. If test light goes out when disconnecting a component, replace that component. If test light stays on, repair short to ground in affected circuit.
Turn ignition off. Disconnect PCM harness connector J2. Turn ignition on. Check voltage on PCM harness connector terminals J2B04 and J2B05. If voltage is present, repair short to voltage in affected circuits. If voltage is not present, replace PCM.

When attempting to diagnose an intermittent problem, use scan tool to review malfunction history diagnostic information. This data can be used to duplicate a problem.

If DTC P0108, P0122, P0452, P0453, P0563, P1106 or P1122 is present, a short to battery voltage in the 5-volt reference circuit is possible. If a short exists while attempting to diagnose DTC, PDT communications will be lost and driveability problems will exist.

DTC P1635: 5-VOLT REFERENCE "A" CIRCUIT (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) monitors 5-volt reference "A" circuit. If voltage is out of tolerance, DTC P1635 will set.

DTC will set when PCM detects a voltage out of range/tolerance on the 5-volt reference circuit and condition is present longer than 10 seconds.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(ref-132811-S27457185922002013000000) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Inspect PCM engine grounds. Ensure grounds are clean and tight. Repair as necessary. After repairs, go to step 12 . If grounds are okay, go to next step.
Check if any other DTCs are set. If any other DTCs are set, diagnose DTCs as necessary. If multiple sensor DTCs are set, check for open or shorts in circuits common to all sensors (5-volt reference and sensor ground circuits). If no other DTCs are set, go to next step.
Turn ignition off. Disconnect PCM harness connector. Turn ignition on. Using DVOM, check voltage between sensor ground circuit and 5-volt reference "A" circuit terminals at PCM connector. If voltage reading is greater than 5 volts, go to next step. If voltage reading is not greater than 5 volts, go to step 9 .
Ensure DVOM is still connected between sensor ground circuit and 5-volt reference "A" circuit terminals at PCM connector. Observe DVOM and disconnect EGR valve connector. If voltage reading is greater than 5 volts, go to next step. If voltage reading is not greater than 5 volts, go to step 8 .
Observe DVOM and disconnect TP sensor connector. Again, observe DVOM and disconnect MAP sensor connector. If voltage changes when one of the sensors is disconnected, locate and repair short to voltage in suspect sensor signal circuit. After repairs, go to step 12 . If voltage does not change when sensors are disconnected, go to next step.
Turn ignition off. Disconnect PCM harness connector. Turn ignition on. Check 5-volt reference "A" circuit for a short to voltage. Repair as necessary. After repairs, go to step 12 . If circuit is okay, go to step 11 .
Replace EGR valve. After replacing EGR valve, go to step 12 .
If voltage reading is less than 4.5 volts, go to next step. If voltage reading is not less than 4.5 volts, go to step 11 .
Turn ignition off. Disconnect PCM harness connector. Check for short to ground in 5-volt reference "A" circuit. Repair as necessary. After repairs, go to step 12 . If circuit is okay, go to next step.
Replace PCM. Program replacement PCM using required equipment. After repair is completed, go to next step.
Using scan tool, select CLEAR INFO or CLEAR DTCs function to 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 this DTC until DTC test runs. If scan tool indicates that this DTC FAILED THIS IGN, repeat step 2 . If scan tool does not indicate that this DTC FAILED THIS IGN, repair is complete.

DTC P1635: 5-VOLT REFERENCE "A" CIRCUIT (3.5L "W" BODY)

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

Powertrain Control Module (PCM) monitors 5-volt reference "A" circuit. If voltage is out of tolerance, DTC P1635 will set. The 5-volt reference "A" circuit feeds to the TP sensor, MAP sensor and EGR pintle position sensor.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(ref-132811-S27457185922002013000000) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Inspect PCM and engine grounds. Ensure grounds are clean and tight. Repair as necessary. After repairs, go to step 11 . If grounds are okay, go to next step.
Check if any other DTCs are set. If any other DTCs are set, diagnose affected DTCs. If no other DTCs are set, go to next step.
Turn ignition off. Disconnect harness connector to TP, MAP, EGR and oil pressure sensor. Turn ignition on. Using DVOM, check voltage between sensor ground circuit and 5-volt reference "A" circuit terminals of each sensor. If voltage reading is 4.5-5.5 volts, go to next step. If voltage reading is not 4.5-5.5 volts, go to step 8 .
Reconnect one disconnected component at a time while check voltage on 5-volt reference circuit at one of the other sensors. If sensor being reconnected causes voltage to go out of range (4.5-5.5 volts), go to next step. If voltage does not go out of range, see «DIAGNOSTIC AIDS»(/gmc/savana/i-1996-2002/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p1537-u1193) .
Check for short to power or ground on circuit to affected sensor/component. Repair as necessary. After repairs, go to step 11 . If circuit is okay, go to next step.
Replace affected sensor/component. After repairs, go to step 11 .
Turn ignition on. Disconnect PCM harness connector. Turn ignition on. Check 5-volt reference "A" circuit for short to ground or power. Repair as necessary. After repairs, go to next step. If circuit is okay, go to step 10 .
Repair 5-volt reference circuit. After repairs, go to step 11 .
Replace PCM. Program replacement PCM using required equipment. After repair is completed, go to next step.
Using scan tool, select CLEAR INFO or CLEAR DTCs function to 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 P1635 until DTC P1635 test runs. If scan tool indicates FAILED THIS IGN, repeat step 2 . If scan tool does not indicate FAILED THIS IGN, go to next step.
Using scan tool, select CAPTURED INFO function. If any undiagnosed DTCs are set, go to affected DTC test.

DTC P1635: 5-VOLT REFERENCE "A" CIRCUIT (3.8L "C", "F", "G", "H" & "W" BODIES)

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

PCM uses 5-volt reference "A" circuit as a sensor feed for EGR valve pintle position, fuel tank pressure (VIN K), MAP, and TP sensors. PCM monitors voltage on this circuit. If PCM senses voltage out of tolerance, DTC P1635 sets.

Conditions for setting DTC are: PCM detects an out of tolerance condition on the 5-volt reference "A" and condition is present longer than 10 seconds.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(ref-132811-S27457185922002013000000) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Ensure PCM and engine grounds are secure and clean. If a problem is found, go to step 14 . If no problem is found, go to next step.
Using scan tool, select DTC INFO, LAST TST FAIL. If DTC P0107, P0108, P0122, P0123, P1106, P1107, P1121, P1122 and/or P1406 also set, diagnose affected DTC before proceeding. If none of these DTCs are set, go to next step.
Turn ignition off. Disconnect PCM connectors. Turn ignition on. Using a DVOM, check voltage between PCM harness connector ground and 5-volt reference "A" circuits. If voltage reading is greater than 5.5 volts, go to next step. If voltage reading is not greater than 5.5 volts, go to step 9 .
Using DVOM, check voltage between PCM harness connector ground and 5-volt reference "A" circuits. Disconnect EGR valve. If voltage is greater than 5.5 volts, go to next step. If voltage is not greater than 5.5 volts, go to step 8 .
Using DVOM, check voltage between PCM harness connector ground and 5-volt reference "A" circuits while sequentially disconnecting fuel tank pressure (VIN K), MAP and TP sensors. If voltage changes whenever any of these sensors is disconnected, locate and repair short to voltage in affected sensor signal circuit and go to step 14 . If voltage does not change, go to next step.
Turn ignition off. Disconnect PCM harness connectors. Turn ignition on. Check 5-volt reference "A" circuit for short to voltage. Repair as necessary. After repairs, go to step 14 . If circuit is okay, go to step 13 .
Replace EGR valve. After replacing EGR valve, go to step 14 .
Turn ignition off. Reconnect PCM. Disconnect TP sensor, MAP sensor, EGR valve and fuel tank pressure sensor. Turn ignition on. Connect DVOM between TP sensor 5-volt reference circuit and TP sensor ground circuit. If voltage reading is less than 4.5 volts, go to step 12 . If voltage reading is not less than 4.5 volts, go to next step.
With DVOM still connected to TP sensor 5-volt reference and ground circuits, reconnect (one at a time) MAP sensor, EGR valve and fuel tank pressure sensor. If voltage changes when one of the listed devices is reconnected, replace that component. After repairs, go to step 14 . If voltage does not change, go to next step.
Disconnect EGR valve. Connect DVOM between EGR connector 5-volt reference circuit and ground circuit. Reconnect TP sensor. If voltage measured on EGR connector changes, replace TP sensor. After replacing sensor, go to step 14 . If voltage measured on EGR connector does not change, go to step 13 .
Turn ignition off. Disconnect PCM harness connectors. Turn ignition on. Check 5-volt reference "A" circuit for short to ground. Repair as necessary. After repairs, go to step 14 . If circuit is okay, go to next step.
Replace PCM. Program replacement PCM using required equipment. After replacing PCM, 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 this DTC. If scan tool indicates that this DTC FAILED THIS IGN, return to step 2 . If scan tool does not indicate that this DTC FAILED THIS IGN, repair is complete.

Check for faulty connections or damaged harness. Observe scan tool MAP display while moving harness and connectors related to EGR valve, fuel tank pressure, MAP and TP sensors. A change in scan tool display indicates fault location.

DTC P1635: 5-VOLT REFERENCE NO. 1 CIRCUIT (4.8L, 5.3L & 6.0L "C" & "K" SERIES)

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

PCM uses a common 5-volt reference No. 1 circuit as a sensor feed to A/C pressure, MAP, EGR, TP sensor, and fuel tank level and pressure sensors. PCM monitors voltage on 5-volt reference No. 1 circuit. If voltage is out of range, DTC will set.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(ref-132811-S27457185922002013000000) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Install scan tool. Start and operate engine at idle for 2 minutes. Using scan tool, monitor DTC. If DTCs P1635 and P1639 fail this ignition cycle, go to step 5 . If DTCs P1635 and P1639 did not fail in this ignition cycle, go to next step.
If only DTC P1635 failed in this ignition cycle, go to step 9 . If DTC P1635 did not fail in this ignition cycle, go to next step.
Turn ignition off, with engine off. Using scan tool, review FREEZE FRAME and/or FAILURE RECORDS data for this DTC and observe parameters. Turn ignition off for 15 seconds, then start engine. Operate vehicle within conditions for setting this DTC. Using scan tool, select DTC option and SPECIFIC DTC option, then enter DTC P1635 and P1639 to determine if both DTCs set at the same time. If scan tool indicates that DTC P1635 or P1635 and P1639 set in this ignition cycle, go to next step. If scan tool does not indicate that DTC P1635 or P1635 and P1639 was set in this ignition cycle, see «DIAGNOSTIC AIDS»(/gmc/savana/i-1996-2002/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p1537-u1193) .
Using scan tool, monitor voltages for fuel level sensor, fuel tank pressure sensor, EGR position sensor, TP sensor and MAP sensor. If voltage reading is 5 volts or greater, go to step 16 . If voltage reading is not 5 volts or greater, go to next step.
Turn ignition on, with engine off. Using scan tool, monitor voltages for MAP sensor, TP sensor, EGR position sensor, fuel tank pressure sensor and fuel level sensor. Using scan tool, enable fuel pump. If any of the voltages increase when fuel pump is turned on, go to step 11 . If voltages do not increase when fuel pump is turned on, go to next step.
Turn ignition off. Disconnect PCM harness connector. Turn ignition on, with engine off. Using a DVOM connected to ground, probe each 5-volt reference circuit at PCM harness connector for MAP sensor, EGR sensor, fuel tank pressure sensor and TP sensor. If voltage readings are greater than 5.1 volts, go to step 12 . If voltage readings are not greater than 5.1 volts, go to next step.
Remove IGN 0 fuse (located in left underdash fuse block) and ECM 1 and ECM "B" fuses (located in underhood electrical center). Disconnect harness connectors from MAP sensor, TP sensor, EGR, fuel level sensor and fuel tank pressure sensor. Using DVOM, check resistance of each 5-volt reference circuit between component connector to PCM harness connector. If any of the resistance is 0-2 ohms, go to step 13 . If any of the resistance is not 0-2 ohms, go to step 15 .
Turn ignition off. Disconnect PCM harness connector. Using a test light connected to battery voltage, probe test light MAP and EGR sensor 5-volt reference circuit. If test light illuminates, go to step 14 . If test light does not illuminate, go to next step.
Using DVOM, check resistance of each 5-volt reference circuit between component connector to PCM harness connector. If any of the resistance is 0-2 ohms, go to step 13 . If any of the resistance is not 0-2 ohms, go to step 15 .
Repair short to ground between fuel pump circuit and appropriate 5-volt reference circuit or signal circuit. After repairs, go to step 17 .
Repair short to voltage on appropriate 5-volt reference circuit. After repairs, go to step 17 .
Repair short between appropriate 5-volt reference circuit and PCM circuit that had continuity. After repairs, go to step 17 .
Repair short to ground on appropriate 5-volt reference circuit. After repairs, go to step 17 .
Replace PCM. Program replacement PCM using required equipment. After replacing PCM, go to step 17 .
Repair short to voltage on appropriate signal circuit. After repairs, go to next step.
Using scan tool, select DTC, CLEAR INFO function. Start and warm engine to normal operating temperature. Select DTC, SPECIFIC, then enter this DTC. 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, repeat step 2 .
Using scan tool, select CAPTURE INFO, REVIEW INFO function. If any undiagnosed DTCs are displayed, go to applicable DTC test.

DTC P1635: 5-VOLT REFERENCE NO. 1 CIRCUIT (5.7L "F" BODY)

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

PCM uses a common 5-volt reference No. 1 circuit as a sensor feed to A/C pressure, MAP, Engine Oil Pressure (EOP) and left tank fuel level sensors. PCM monitors voltage on 5-volt reference No. 1 circuit. If voltage is out of range, DTC will set.

DTC will set when PCM detects 5-volt reference No. 1 circuit is out of range and condition is met for greater than 2 seconds.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(ref-132811-S27457185922002013000000) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Start and operate engine at idle for 2 minutes. Using scan tool, monitor DTC. If both DTCs P1635 and P1639 fails this ignition, go to step 5 . If only DTC P1639 did not fail this ignition, go to next step.
If DTC P1635 failed this ignition, go to step 9 . If DTC P1635 did not fail this ignition, go to next step.
Turn ignition on, with engine off. Using scan tool, review FREEZE FRAME and/or FAILURE RECORDS data for this DTC and observe parameters. Turn ignition off for 15 seconds. Start engine. Operate vehicle within conditions for setting this DTC and as close to conditions recorded in Freeze Frame/Failure Records. Select DTC option, SPECIFIC DTC option, then enter this DTC on scan tool. Select DTC P1635 and P1639 to determine if both DTCs set at the same time. If scan tool indicates that DTC P1635 or P1635 and P1639 set in this ignition, go to next step. If scan tool does not indicate that DTC P1635 or P1635 and P1639, see «DIAGNOSTIC AIDS»(/gmc/savana/i-1996-2002/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p1537-u1193) .
Allow engine to idle. Using scan tool, monitor voltages for fuel level sensor(s), fuel tank pressure sensor, EGR pintle position sensor, TP sensor, A/C refrigerant pressure sensor and MAP sensor. If any of the voltage reading is 5 volts or greater, go to step 18 . If any of the voltage reading is not 5 volts or greater, go to next step.
Turn ignition off, with engine off. Using scan tool, monitor voltages for fuel level sensor(s), fuel tank pressure sensor, engine oil pressure sensor, A/C refrigerant pressure sensor and MAP sensor. If any of the voltages increase when fuel pump was turned on, go to step 11 . If any of the voltages does not increase when fuel pump was turned on, go to next step.
Turn ignition off. Disconnect PCM harness connector. Turn ignition on, with engine off. Using DVOM, check voltage between ground and each 5-volt reference circuit at PCM harness connector for fuel tank pressure sensor, engine oil pressure sensor, A/C refrigerant pressure sensor and MAP sensor. If any of the circuits measure greater than 5.1 volts, go to step 12 . If any of the circuits does not measure greater than 5.1 volts, go to next step.
Turn ignition off. Remove fuses to PCM ignition and BCM battery. Disconnect harness connectors to MAP, TP, EGR, fuel level, fuel tank pressure and A/C refrigerant pressure sensors. Check resistance between each 5-volt reference circuit to all other PCM circuits at PCM harness connector. If any of the circuits indicate a resistance of 0-2 ohms, go to step 13 . If any of the circuits does not indicate a resistance of 0-2 ohms, go to step 15 .
Turn ignition off. Disconnect PCM harness connector. Using test light connected to battery voltage, probe test light to PCM harness connector 5-volt reference circuits to MAP and EGR sensors. If test light illuminates on any of the circuits, go to step 14 . If test light does not illuminate on any of the circuits, go to next step.
Check resistance from each 5-volt reference circuit to all other PCM circuits at PCM harness connector. If any of the circuits indicate a resistance of 0-2 ohms, go to step 13 . If any of the circuits does not indicate a resistance of 0-2 ohms, go to step 15 .
Repair short between fuel pump circuit and appropriate 5-volt reference circuit. After repairs, go to step 19 .
Repair short to voltage on appropriate 5-volt reference circuit. After repairs, go to step 19 .
Repair short to voltage between appropriate 5-volt reference circuit and PCM circuit that had continuity. After repairs, go to step 19 .
Repair short to ground on appropriate 5-volt reference circuit. After repairs, go to step 19 .
Reconnect PCM harness connector. Using scan tool, clear DTCs. Start and operate engine at idle. Using scan tool, monitor DTCs while disconnecting the following components one at a time: MAP, TP, EGR, fuel level, fuel tank pressure and A/C refrigerant pressure sensors. If scan tool indicates that DTC P1635/P1639 passed with component disconnected, go to next step. If scan tool does not indicate that DTC P1635/P1639 passed with component disconnected, go to step 17 .
Replace components for which DTC passed. After replacing component, go to step 19 .
Replace PCM. Program replacement PCM using required equipment. After replacing PCM, go to next step.
Repair short to voltage on appropriate signal circuit. After repairs, go to next step.
Using scan tool, select DTC, CLEAR INFO function. Start and warm engine to normal operating temperature. Select DTC, SPECIFIC, then enter this DTC. 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, repeat step 2 .
Using scan tool, select CAPTURE INFO, REVIEW INFO function. If any undiagnosed DTCs are displayed, go to applicable DTC test.

DTC P1635: 5-VOLT REFERENCE NO. 1 CIRCUIT (5.7L "Y" BODY)

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

DTC will set when PCM detects 5-volt reference No. 1 circuit is out of range and condition is met for greater than 2 seconds.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(ref-132811-S27457185922002013000000) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Start and operate engine for 2 minutes. Using scan tool, monitor DTC. If both DTCs P1635 and P1639 fails this ignition, go to step 5 . If only DTC P1639 did not fail this ignition, go to next step.
If DTC P1635 failed this ignition, go to step 9 . If DTC P1635 did not fail this ignition, go to next step.
Turn ignition on, with engine off. Using scan tool, review FREEZE FRAME and/or FAILURE RECORDS data for this DTC and observe parameters. Turn ignition off for 15 seconds. Start engine. Operate vehicle within conditions for setting this DTC and as close to conditions recorded in Freeze Frame/Failure Records. Select DTC option, SPECIFIC DTC option, then enter this DTC on scan tool. Select DTC P1635 and P1639 to determine if both DTCs set at the same time. If scan tool indicates that DTC P1635 or P1635 and P1639 set in this ignition, go to next step. If scan tool does not indicate that DTC P1635 or P1635 and P1639, see «DIAGNOSTIC AIDS»(/gmc/savana/i-1996-2002/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p1537-u1193) .
Allow engine to idle. Using scan tool, monitor voltages for fuel level sensor(s), fuel tank pressure sensor, engine oil pressure sensor, A/C refrigerant pressure sensor and MAP sensor. If any of the voltage reading is at 5 volts or greater, go to step 15 . If any of the voltage reading is not 5 volts or greater, go to next step.
Turn ignition off, with engine off. Using scan tool, monitor voltages for fuel level sensor(s), fuel tank pressure sensor, engine oil pressure sensor, A/C refrigerant pressure sensor and MAP sensor. If any of the voltages increase when fuel pump was turned on, go to step 11 . If any of the voltages does not increase when fuel pump was turned on, go to next step.
Turn ignition off. Disconnect PCM harness connector. Turn ignition on, with engine off. Using DVOM, check voltage between ground and each 5-volt reference circuit at PCM harness connector for fuel tank pressure sensor, engine oil pressure sensor, A/C refrigerant pressure sensor and MAP sensor. If any of the circuits measure greater than 5.1 volts, go to step 12 . If any of the circuits does not measure greater than 5.1 volts, go to next step.
Turn ignition off. Check resistance between each 5-volt reference circuit to all other PCM circuits at PCM harness connector. If any of the circuits indicate a resistance of 0-2 ohms, go to step 13 . If any of the circuits does not indicate a resistance of 0-2 ohms, go to step 16 .
Turn ignition off. Disconnect PCM harness connector. Using test light connected to battery voltage, probe test light to PCM harness connector 5-volt reference circuits to MAP sensor and engine oil pressure sensor. If test light illuminates on any of the circuits, go to step 14 . If test light does not illuminate on any of the circuits, go to next step.
Check resistance from each 5-volt reference circuit to all other PCM circuits at PCM harness connector. If any of the circuits indicate a resistance of 0-2 ohms, go to step 13 . If any of the circuits does not indicate a resistance of 0-2 ohms, go to step 16 .
Repair short between fuel pump circuit and appropriate 5-volt signal or reference circuit. After repairs, go to step 17 .
Repair short to voltage on appropriate 5-volt reference circuit. After repairs, go to step 17 .
Repair short between appropriate 5-volt reference circuit and PCM circuit that had continuity. After repairs, go to step 17 .
Repair short to ground on appropriate 5-volt reference circuit. After repairs, go to step 17 .
Repair short to voltage on appropriate signal circuit. After repairs, go to step 17 .
Replace PCM. Program replacement PCM using required equipment. After replacing PCM, go to next step.
Using scan tool, select DTC, CLEAR INFO function. Start and warm engine to normal operating temperature. Select DTC, SPECIFIC, then enter this DTC. 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, repeat step 2 .
Using scan tool, select CAPTURE INFO, REVIEW INFO function. If any undiagnosed DTCs are displayed, go to applicable DTC test.

DTC P1637: GENERATOR LIGHT CIRCUIT FAULT (3.4L "U" SERIES)

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

Output Driver Modules (ODMs) are used by PCM to turn on many of the current-driven devices that are needed to control various engine and transmission functions. Each ODM is capable of controlling up to 7 separate outputs by applying ground to the device which the PCM is commanding on. The ODMs have the capability of diagnosing each output circuit individually. DTC will set when there is an improper voltage level on the output circuit that controls the generator light.

A history DTC will clear after 40 consecutive warm-up cycles have occurred without a malfunction. DTC will clear when battery is disconnected or cleared by scan tool.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(ref-132811-S27457185922002013000000) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Check instrument cluster for proper operation. If instrument cluster operation is okay, go to next step. If instrument cluster is faulty, diagnose and repair instrument cluster. See appropriate INSTRUMENT PANELS article in ACCESSORIES & EQUIPMENT.
Turn ignition off. Disconnect PCM harness connector. Turn ignition on, with engine off. Using DVOM, check voltage between ground and affected PCM output circuit at PCM harness connector. If battery voltage is present, go to next step. If battery voltage is not present, go to step 7 .
Set DVOM to 10-amp scale. Check and observe current between ground and affected PCM output circuit for 2 minutes. If reading is 0.05-1.50 amps, go to step 12 . If reading is not 0.05-1.50 amps, go to next step.
Disconnect instrument cluster harness connector. Check voltage between ground and affected PCM output circuit at PCM harness connector. If voltage reading is zero volts, go to step 15 . If voltage reading is not zero volts, go to next step.
Locate and repair short to voltage in affected PCM output circuit. After repairs, go to step 3 .
Check ignition feed fuse for instrument panel cluster indicator lights. If fuse is blown, go to next step. If fuse is okay, go to step 9 .
Locate and repair short to ground in ignition feed circuit for instrument panel cluster indicator lights. Replace fuse. After repairs, go to step 3 .
Disconnect instrument panel cluster harness connector. Turn ignition on, with engine off. Check voltage between ignition feed circuit for instrument panel cluster indicator lights and ground. If voltage reading is about battery voltage, go to next step. If voltage reading is not about battery voltage, go to step 14 .
Check affected PCM output circuit for open or short to ground. Repair as necessary. After repairs, go to step 3 . If circuit is okay, go to next step.
Check affected PCM output circuit and ignition feed circuit for poor connection at instrument panel cluster and at PCM. Repair as necessary. After repairs, go to step 3 . If connections are okay, go to step 15 .
Turn ignition off. Reconnect PCM harness connector. Disconnect instrument panel cluster harness connector. Turn ignition on, with engine off. Using a test light, connect test light between affected PCM output circuit and ignition feed circuit at instrument panel cluster harness connector. Using scan tool in OUTPUTS TEST function, cycle the affected output circuit on and off. If test light flashes on and off, see «DIAGNOSTIC AIDS»(/gmc/savana/i-1996-2002/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p1537-u1193) . If test light does not flash on and off, go to next step.
Check affected PCM output circuit for poor connection at PCM. Repair as necessary. After repairs, go to step 3 . If connections are okay, go to step 16 .
Locate and repair open in ignition feed circuit to instrument panel cluster indicator lights. After repairs, go to step 3 .
Replace instrument panel cluster assembly. After replacing cluster assembly, go to step 3 .
Replace PCM. Program replacement PCM using required equipment. After replacing PCM, go to step 3 .
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 this DTC. If scan tool displays that this DTC FAILED THIS IGN, return to step 3 . If scan tool does not display that this DTC FAILED THIS IGN, system is okay.

Check for poor connection at PCM. Inspect harness connectors for backed-out terminals, improper mating, broken locks or poor terminal-to-wire connection.

DTC P1637: GENERATOR "L" TERMINAL CIRCUIT (4.0L "G" BODY & 4.6L "K" BODY - SEVILLE)

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

PCM monitors the voltage level on the "L" terminal circuit while the generator is commanded on and PCM expects to see battery voltage on this circuit. If PCM monitors a low voltage level in the "L" terminal feedback circuit, indicating that the generator is off, DTC will set.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(ref-132811-S27457185922002013000000) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Ensure battery is fully charged. Disconnect generator harness connector. Start engine. Using DVOM, check voltage between ground and generator harness connector terminal "L". If voltage reading is 10 volts or greater, go to step 9 . If voltage reading is not 10 volts or greater, go to next step.
Store fluid life index as indicated on scan tool. Turn ignition off and wait 30 seconds, then disconnect PCM harness connector C1. Using DVOM, check resistance between ground and generator harness connector terminal "L". If resistance is 10,000 ohms or greater, go to next step. If resistance is not 10,000 ohms or greater, go to step 5 .
Check resistance between generator harness connector terminal "L" and PCM harness connector C1 terminal No. 75. If resistance is 5 ohms or less, go to step 7 . If resistance is not 5 ohms or less, go to step 6 .
Repair short to ground in generator "L" terminal feedback circuit.
Repair open or high resistance in generator "L" terminal feedback circuit.
Check terminal contact at generator "L" terminal feedback circuit terminal of PCM harness connector C1. Repair as necessary. If terminal contact is okay, go to next step.
Replace PCM. Program replacement PCM using required equipment.
Turn ignition off. Check record voltage between underhood battery positive junction block and ground. Check voltage between generator harness connector terminal "S" and ground. If voltage readings are within one volt of each other, go to step 11 . If voltage readings are not within one volt of each other, go to next step.
Repair open or high resistance in circuit to battery temperature sensor or battery temperature sensor.
Repair or replace generator.

DTC P1637 and a low battery charge may be caused by a generator fault, such as a shorted output diode, malfunctioning regulator, open or shorted rotor, or open sense lead. This DTC will not set if generator "L" terminal circuit is shorted to voltage, but may cause a parasitic load on the battery with ignition off.

DTC P1637: GENERATOR "L" TERMINAL CIRCUIT (4.8L, 5.3L & 6.0L "C" & "K" SERIES)

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

PCM monitors the voltage level on the generator "L" terminal circuit while the generator is commanded on and PCM expects to see battery voltage on this circuit. If PCM monitors a low voltage level in the generator "L" terminal feedback circuit, indicating that the generator is off, DTC will set.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(ref-132811-S27457185922002013000000) 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 generator "L" parameter. If scan tool indicates that generator "L" terminal is inactive, go to next step. If scan tool does not indicate that generator "L" terminal is inactive, see «DIAGNOSTIC AIDS»(/gmc/savana/i-1996-2002/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p1537-u1193) .
Using a test light connected to ground, probe generator battery feed circuit. If test light illuminates, go to next step. If test light does not illuminate, diagnose charging system.
Disconnect generator harness connector. Start engine. Check voltage between ground and generator harness connector terminal "B". If voltage reading is 10 volts or greater, go to step 11 . If voltage reading is not 10 volts or greater, go to next step.
Turn ignition off. Disconnect PCM harness connector. Check continuity between generator circuit at PCM and generator harness connector terminal "B". If continuity exists, go to next step. If continuity does not exists, go to step 8 .
Check continuity between battery ground and generator harness connector terminal "B". If continuity exists, go to next step. If continuity does not exist, go to step 9 .
Repair short to ground in generator circuit. After repairs, go to step 13 .
Repair open/high resistance in generator circuit. After repairs, go to step 13 .
Check terminal contact at PCM harness connector. Repair as necessary. After repairs, go to step 13 . If terminal contact is okay, go to next step.
Replace PCM. Program replacement PCM using required equipment.
Check terminal contact at generator harness connector. Repair as necessary. After repairs, go to step 13 . If connectors are okay, go to next step.
Repair or replace generator. After repairing or replacing generator, go to next step.
Using scan tool, select DTC, CLEAR INFO function. Start and warm engine to normal operating temperature. Select DTC, SPECIFIC, then enter this DTC. 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, repeat step 2 .
Using scan tool, select CAPTURE INFO and REVIEW INFO option. If any undiagnosed DTCs are set, diagnose affected DTCs.

PCM applies ignition voltage to generator "L" terminal circuit. A small amount of current flows from this circuit through the generator windings to ground to create a magnetic field which starts the generator process. When generator is at operating speed and producing voltage, a solid state switch for the "L" terminal circuit in the generator opens and the PCM detects that the initial start-up current flow has stopped.

PCM expects to detect low voltage on "L" terminal circuit prior to the generator rotating at operating speed and conversely expects that circuit to be at ignition voltage potential when generator is operational. When PCM detects a fault (circuit shorted to ground or circuit shorted to voltage), the BATTERY light will illuminate.

DTC will set when PCM detects an improper voltage on generator "L" terminal circuit.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(ref-132811-S27457185922002013000000) 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 generator "L" terminal parameter. If scan tool displays that generator "L" is inactive, go to next step. If scan tool does not display that generator "L" is inactive, see «DIAGNOSTIC AIDS»(/gmc/savana/i-1996-2002/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p1537-u1193) .
Using a test light connected to ground, probe generator battery feed circuit. If test light illuminates, go to next step. If test light does not illuminate, diagnose charging system. See appropriate GENERATORS & REGULATORS article in STARTING & CHARGING SYSTEMS.
Turn ignition off. Disconnect generator harness connector. Start engine. Check voltage to ground at generator harness connector terminal "B". If voltage reading is 10 volts or greater, go to step 11 . If voltage is not 10 volts or greater, go to next step.
Turn ignition off. Disconnect PCM harness connector. Check continuity between generator harness connector terminal "B" and PCM harness connector. If continuity exists, go to next step. If continuity does not exist, go to step 8 .
Check continuity between battery ground and generator harness connector terminal "B". If continuity exists, go to next step. If continuity does not exist, go to step 9 .
Repair short to ground in generator circuit. After repairs, go to step 13 .
Repair open/high resistance in generator circuit. After repairs, go to step 13 .
Check for poor connections at PCM harness connector. Repair as necessary. After repairs, go to step 13 . If connections are okay, go to next step.
Replace PCM. Program replacement PCM using required equipment.
Check for poor connections at generator harness connector. Repair as necessary. After repairs, go to step 13 . If connections are okay, go to next step.
Replace generator. After replacing generator, 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 this DTC. If scan tool displays that this DTC FAILED THIS IGN, return to step 2 . If scan tool does not display that this DTC FAILED THIS IGN, go to next step.
Using scan tool, select CAPTURE INFO and REVIEW INFO option. If any undiagnosed DTCs are set, diagnose affected DTCs.

An intermittent problem can be caused by misrouted harness, rubbed-through wire insulation or broken wire inside insulation. A generator fault, such as a shorted output diode, malfunctioning regulator, open or shorted rotor, or open sense lead or battery feed may cause a low battery charge.

DTC P1637: GENERATOR "L" TERMINAL CIRCUIT (5.7L "Y" BODY)

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

Conditions for setting DTC are: PCM detects the "L" terminal as active with ignition on and engine not running or PCM detects the "L" terminal as inactive with engine running and all conditions present for 6 seconds.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(ref-132811-S27457185922002013000000) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Ensure battery is fully charged. Turn ignition on, with engine off. Using scan tool, monitor DTC information. If DTC P1637 and/or P1638 failed in this ignition cycle, go to step 4 . If DTC P1637 and/or P1638 did not fail in this ignition cycle, go to next step.
Start and operate engine at idle. Using scan tool, monitor DTC information. If DTC P1637 and/or P1638 failed in this ignition cycle, go to next step. If DTC P1637 and/or P1638 did not fail in this ignition cycle, see «DIAGNOSTIC AIDS»(/gmc/savana/i-1996-2002/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p1537-u1193) .
Turn ignition off. Disconnect generator 4-pin harness connector. Turn ignition on, with engine off. Using test light connected to ground, probe generator sensor circuit (terminal "S") and generator battery feed circuit (mounted on rear of generator). If test light illuminates on both circuits, go to next step. If test light does not illuminate on both circuits, diagnose charging system. See appropriate GENERATORS & REGULATORS article in STARTING & CHARGING SYSTEMS.
Turn ignition off. Reconnect 4-pin harness connector. Turn on, with engine off. Using scan tool in ENGINE 3 DATA LIST, monitor "L" terminal parameter. If scan tool displays that "L" terminal as inactive, go to next step. If scan tool does not display that "L" terminal as inactive, go to step 8 .
Using scan tool in ENGINE 3 DATA LIST, monitor "F" terminal parameter. If scan tool displays that "F" terminal is less than 40 percent, go to next step. If scan tool displays that "F" terminal is not less than 40 percent, go to step 13 .
Start and operate engine at idle. Using scan tool, monitor "L" terminal parameter. If scan tool displays that "L" terminal as inactive, go to step 14 . If scan tool does not display that "L" terminal as inactive, go to step 10 .
Turn ignition off. Disconnect generator 4-pin harness connector. Jumper "L" terminal at harness connector to ground. Using scan tool, monitor "L" terminal. If scan tool displays that "L" terminal as inactive, go to step 20 . If scan tool does not display that "L" terminal as inactive, go to next step.
Turn ignition off. Disconnect PCM harness connector. Check resistance of "L" terminal circuit from PCM harness connector to generator harness connector. If resistance is 0-2 ohms, go to step 18 . If resistance is not 0-2 ohms, go to step 15 .
Disconnect generator 4-pin harness connector. Using a test light connected to battery voltage, probe test light to generator "F" terminal at generator harness connector. Using scan tool, monitor "F" terminal. If generator "F" terminal parameter changes from 0-99 percent, go to step 20 . If generator "F" terminal parameter does not change from 0-99 percent, go to next step.
Check resistance between battery ground and "F" terminal circuit at generator harness connector. If resistance is 0-10 ohms, go to step 16 . If resistance is not 0-10 ohms, go to next step.
Turn ignition off. Disconnect PCM harness connector. Check resistance of "F" terminal circuit between PCM harness connector and generator harness connector. If resistance is 0-2 ohms, go to step 18 . If resistance is not 0-2 ohms, go to step 15 .
Disconnect generator 4-pin harness connector. Using scan tool, monitor "F" terminal parameter. If parameter is zero percent, go to step 21 . If parameter is not zero percent, go to step 17 .
Disconnect generator 4-pin harness connector. Using scan tool, monitor "L" terminal parameter. If scan tool indicates that "L" terminal parameter is inactive, go to step 16 . If scan tool does not indicate that "L" terminal parameter is inactive, go to step 21 .
Repair open/high resistance is generator circuit. After repairs, go to step 22 .
Repair short to ground in generator circuit. After repairs, go to step 22 .
Repair short to voltage in "F" terminal circuit. After repairs, go to step 22 .
Check for poor connection at PCM harness connector. Repair as necessary. After repairs, go to step 22 . If connections are okay, go to next step.
Replace PCM. Program replacement PCM using required equipment.
Check for poor connection at generator harness connector. Repair as necessary. After repairs, go to step 22 . If connection is okay, go to next step.
Replace generator. After replacing generator, 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 this DTC. If scan tool displays that this DTC FAILED THIS IGN, return to step 2 . If scan tool does not display that this DTC FAILED THIS IGN, go to next step.
Using scan tool, select CAPTURE INFO and REVIEW INFO option. If any undiagnosed DTCs are set, diagnose affected DTCs.

An intermittent problem can be caused by misrouted harness, rubbed-through wire insulation or broken wire inside insulation. DTCs P1637 and P1638 may set at the same time depending on failure. Also, the "L" terminal circuit can cause DTC P1638 to set.

A generator fault, such as a shorted output diode, malfunctioning regulator, open or shorted rotor, or open sense lead or battery feed may cause a low battery charge.

DTC P1638: GENERATOR "F" TERMINAL CIRCUIT (4.0L "G" BODY & 4.6L "K" BODY - SEVILLE)

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

This test monitors the field voltage of the generator. The generator is able to produce the desired voltage by varying the duty cycle of the field current. At low engine speeds, the field may have a duty cycle of 90 percent. At higher engine speeds and lower electrical loads, the duty cycle will be less. The generator produces a Pulse Width Modulated (PWM) signal that is monitored by the PCM on the generator "F" terminal feedback circuit. This duty cycle signal is sent to the PCM, and if it falls to less than a certain duty cycle for too long, DTC will set.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(ref-132811-S27457185922002013000000) 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 of DTC P0560 is also present. If DTC P0560 is present, diagnose this DTC first. If this DTC is not present, go to next step.
Start and idle engine for 2 minutes. Using scan tool in DTC INFO mode, select FAIL THIS IGN. If this DTC failed in this ignition cycle, go to next step. If this DTC did not fail in this ignition cycle, fault is not present.
Turn ignition on, with engine off. In ENGINE 1 mode, note GEN F TERMINAL display on scan tool. If duty cycle reading on scan tool is zero percent or greater, go to next step. If scan tool reading is zero percent, go to step 6 .
If duty cycle is less than 5 percent, diagnose generator. See appropriate GENERATORS & REGULATORS article in STARTING & CHARGING SYSTEMS. If duty cycle is greater than 5 percent, go to step 12 .
Store fluid life index as indicated on scan tool. Turn ignition off and wait 30 seconds, then disconnect PCM harness connector C1. Turn ignition on. Using DVOM, check voltage between ground and generator "F" terminal feedback circuit at PCM harness connector C1 terminal. If voltage reading is 0.1 volt or greater, go to step 9 . If voltage reading is not 0.1 volt or greater, go to next step.
Check resistance between ground and generator "F" terminal feedback circuit on PCM harness connector C1 terminal. If resistance is less than 10,000 ohms, go to step 10 . If resistance is not less than 10,000 ohms, go to next step.
Check generator "F" terminal feedback circuit resistance between PCM and generator harness connector terminals. If resistance is 5 ohms or less, diagnose generator. See appropriate GENERATORS & REGULATORS article in STARTING & CHARGING SYSTEMS. If resistance is greater than 5 ohms, go to step 11 .
Replace short to voltage in generator "F" terminal feedback circuit.
Repair short to ground in generator "F" terminal feedback circuit.
Repair open in generator "F" terminal feedback circuit.
Check terminal contact at generator harness connector. Repair as necessary. If terminal connector is okay, go to next step.
Check terminal contact at PCM harness connector C1. Repair as necessary. If terminal contact is okay, go to next step.
Replace PCM. Program replacement PCM using required equipment.

DTC P1638: GENERATOR "F" TERMINAL CIRCUIT (5.7L "Y" BODY)

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

The "F" terminal inputs to the PCM to indicate percentage of total capacity that the generator is producing. The signal is detected by the PCM as a duty cycle from the generator and displayed on scan tool as a percentage. PCM can monitor the generator's output under all conditions to determine if it is functioning normally.

A low duty cycle percentage is displayed when there is low demand on generator. A high load on generator will indicate a duty cycle close to 100 percent. A normally functioning generating system will never reach a 100 percent duty cycle, as indicated on scan tool.

Conditions for setting DTC are: "F" terminal indicates a duty cycle not between 10 and 40 percent with ignition on and engine off or duty cycle is less than 5 percent with engine running and conditions met for 6 seconds.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(ref-132811-S27457185922002013000000) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Ensure battery is fully charged. Turn ignition on, with engine off. Using scan tool, monitor DTC information. If DTC P1637 and/or P1638 failed in this ignition cycle, go to step 4 . If DTC P1637 and/or P1638 did not fail in this ignition cycle, go to next step.
Start and operate engine at idle. Using scan tool, monitor DTC information. If DTC P1637 and/or P1638 failed in this ignition cycle, go to next step. If DTC P1637 and/or P1638 did not fail in this ignition cycle, see «DIAGNOSTIC AIDS»(/gmc/savana/i-1996-2002/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p1537-u1193) .
Turn ignition off. Disconnect generator 4-pin harness connector. Turn ignition on, with engine off. Using test light connected to ground, probe generator sensor circuit (terminal "S") and generator battery feed circuit (mounted on rear of generator). If test light illuminates on both circuits, go to next step. If test light does not illuminate on both circuits, diagnose charging system. See appropriate GENERATORS & REGULATORS article in STARTING & CHARGING SYSTEMS.
Turn ignition off. Reconnect 4-pin harness connector. Turn on, with engine off. Using scan tool in ENGINE 3 DATA LIST, monitor "L" terminal parameter. If scan tool displays that "L" terminal as inactive, go to next step. If scan tool does not display that "L" terminal as inactive, go to step 8 .
Using scan tool in ENGINE 3 DATA LIST, monitor "F" terminal parameter. If scan tool displays that "F" terminal is less than 40 percent, go to next step. If scan tool displays that "F" terminal is not less than 40 percent, go to step 13 .
Start and operate engine at idle. Using scan tool, monitor "L" terminal parameter. If scan tool displays that "L" terminal as inactive, go to step 14 . If scan tool does not display that "L" terminal as inactive, go to step 10 .
Turn ignition off. Disconnect generator 4-pin harness connector. Jumper "L" terminal at harness connector to ground. Using scan tool, monitor "L" terminal. If scan tool displays that "L" terminal as inactive, go to step 20 . If scan tool does not display that "L" terminal as inactive, go to next step.
Turn ignition off. Disconnect PCM harness connector. Check resistance of "L" terminal circuit from PCM harness connector to generator harness connector. If resistance is 0-2 ohms, go to step 18 . If resistance is not 0-2 ohms, go to step 15 .
Disconnect generator 4-pin harness connector. Using a test light connected to battery voltage, probe test light to generator "F" terminal at generator harness connector. Using scan tool, monitor "F" terminal. If generator "F" terminal parameter changes from 0-99 percent, go to step 20 . If generator "F" terminal parameter does not change from 0-99 percent, go to next step.
Check resistance between battery ground and "F" terminal circuit at generator harness connector. If resistance is 0-10 ohms, go to step 16 . If resistance is not 0-10 ohms, go to next step.
Turn ignition off. Disconnect PCM harness connector. Check resistance of "F" terminal circuit between PCM harness connector and generator harness connector. If resistance is 0-2 ohms, go to step 18 . If resistance is not 0-2 ohms, go to step 15 .
Disconnect generator 4-pin harness connector. Using scan tool, monitor "F" terminal parameter. If parameter is zero percent, go to step 21 . If parameter is not zero percent, go to step 17 .
Disconnect generator 4-pin harness connector. Using scan tool, monitor "L" terminal parameter. If scan tool indicates that "L" terminal parameter is inactive, go to step 16 . If scan tool does not indicate that "L" terminal parameter is inactive, go to step 21 .
Repair open/high resistance is generator circuit. After repairs, go to step 22 .
Repair short to ground in generator circuit. After repairs, go to step 22 .
Repair short to voltage in "F" terminal circuit. After repairs, go to step 22 .
Check for poor connection at PCM harness connector. Repair as necessary. After repairs, go to step 22 . If connections are okay, go to next step.
Replace PCM. Program replacement PCM using required equipment.
Check for poor connection at generator harness connector. Repair as necessary. After repairs, go to step 22 . If connection is okay, go to next step.
Replace generator. After replacing generator, 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 this DTC. If scan tool displays that this DTC FAILED THIS IGN, return to step 2 . If scan tool does not display that this DTC FAILED THIS IGN, go to next step.
Using scan tool, select CAPTURE INFO and REVIEW INFO option. If any undiagnosed DTCs are set, diagnose affected DTCs.

A generator fault, such as a shorted output diode, malfunctioning regulator, open or shorted rotor, or open sense lead or battery feed may cause a low battery charge.

The PCM receives analog voltage signals from various sensors. The Analog/Digital (A/D) converter changes these signals to a digital signal. This DTC sets when the A/D becomes faulty in the TC.

Record and diagnose all DTC(s). Clear DTC(s). If DTC P1639 resets, replace PCM.

DTC P1639: 5-VOLT REFERENCE "B" 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 uses 5-volt reference "B" circuit as a sensor feed for A/C refrigerant pressure sensor. PCM monitors voltage on this circuit. If PCM senses voltage out of tolerance/range, DTC will set.

Conditions required to set DTC are, PCM detects an out of tolerance condition on the 5-volt reference "B" circuit and condition present for longer than 10 seconds.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(ref-132811-S27457185922002013000000) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Ensure PCM and engine grounds are secure and clean. If a problem is found, go to step 11 . If no problem is found, go to next step.
Using scan tool, select DTC INFO, LAST TST FAIL. If DTC P0530 also set, go to DTC P0530. If DTC is not set, go to next step.
Turn ignition off. Disconnect PCM harness connectors. Turn ignition on. Using a DVOM, check voltage between PCM harness connector ground and 5-volt reference "B" circuits. If voltage reading is greater than 5 volts, go to next step. If voltage reading is not greater than 5 volts, go to step 8 .
Using DVOM, check voltage between PCM harness connector ground and 5-volt reference "B" circuits. Disconnect A/C refrigerant pressure sensor. If voltage reading is greater than 5 volts, go to next step. If voltage reading is not greater 5 volts, go to step 7 .
Turn ignition off. Disconnect PCM harness connectors. Turn ignition on. Check 5-volt reference "B" circuit for short to voltage. If short to voltage is found, repair as necessary. After repairs, go to step 11 . If circuit is okay, go to step 10 .
Locate and repair short to voltage in A/C refrigerant pressure sensor signal circuit. After repairs, go to step 11 .
If voltage reading is less than 4.5 volts, go to next step. If voltage reading is not less than 4.5 volts, go to step 10 .
Turn ignition off. Disconnect PCM harness connectors. Turn ignition on. Check 5-volt reference "B" circuit for short to ground. If short to ground is found, repair as necessary. After repairs, go to step 11 . If circuit is okay, go to next step.
Replace PCM. Program replacement PCM using required equipment. After replacing PCM, 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 this DTC. If scan tool displays that this DTC FAILED THIS IGN, return to step 2 . If scan tool does not display that this DTC FAILED THIS IGN, repair is complete.

Check for faulty connections or damaged harness. Observe A/C PRESSURE display on scan tool while moving harness and connectors related to A/C refrigerant pressure sensor. A change in scan tool display indicates fault location.

DTC P1639: 5-VOLT REFERENCE "B" CIRCUIT (3.5L "W" BODY)

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

Powertrain Control Module (PCM) uses the 5-volt reference "B" circuit as a sensor feed for the A/C refrigerant pressure sensor. If voltage is out of tolerance, DTC will set.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(ref-132811-S27457185922002013000000) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Inspect PCM and engine grounds. Ensure grounds are clean and tight. Repair as necessary. After repairs, go to step 11 . If grounds are okay, go to next step.
Check if any other DTCs are set. If other DTCs are set, diagnose affected DTCs. If no other DTCs are set, go to next step.
Turn ignition off. Disconnect harness connector to A/C refrigerant pressure sensor and fuel tank pressure sensor. Turn ignition on. Using DVOM, check voltage between sensor ground circuit and 5-volt reference "A" circuit terminals of one of the sensors. If voltage reading is 4.5-5.5 volts, go to next step. If voltage reading is not 4.5-5.5 volts, go to step 8 .
Reconnect one disconnected component at a time while checking voltage on 5-volt reference circuit at one of the other sensors. If sensor being reconnected causes voltage to go out of range (4.5-5.5 volts), go to next step. If voltage does not go out of range, see «DIAGNOSTIC AIDS»(/gmc/savana/i-1996-2002/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p1537-u1193) .
Check for short to power or ground on circuit to affected sensor/component. Repair as necessary. After repairs, go to step 11 . If circuit is okay, go to next step.
Replace affected sensor/component. After repairs, go to step 11 .
Turn ignition on. Disconnect PCM harness connector. Turn ignition on. Check 5-volt reference "A" circuit for short to ground or power. Repair as necessary. After repairs, go to next step. If circuit is okay, go to step 10 .
Repair 5-volt reference circuit. After repairs, go to step 11 .
Using scan tool, select CLEAR INFO or CLEAR DTCs function to 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 this DTC until DTC test runs. If scan tool indicates FAILED THIS IGN, repeat step 2 . If scan tool does not indicate FAILED THIS IGN, go to next step.
Replace PCM. Program replacement PCM using required equipment. After repair is completed, go to next step.
Using scan tool, select CAPTURED INFO function. If any undiagnosed DTCs are set, go to affected DTC test.

DTC P1639: 5-VOLT REFERENCE "B" CIRCUIT (3.8L "C", "G", "H" & "W" BODIES)

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

PCM uses 5-volt reference "B" circuit as a sensor feed for A/C refrigerant pressure sensor. PCM monitors voltage on this circuit. If PCM senses voltage out of tolerance, DTC P1639 sets.

Conditions required to set DTC are, PCM detects an out of tolerance condition on 5-volt reference "B"circuit and condition present for longer than 10 seconds.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(ref-132811-S27457185922002013000000) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Ensure PCM and engine grounds are secure and clean. If a problem is found, go to step 11 . If no problem is found, go to next step.
Ensure A/C is off. Observe A/C high side pressure on scan tool. If pressure displays a voltage of greater than 4.8 volts or less than 0.1 volt, go to DTC P0530 for diagnosis of pressure sensor circuit. If voltage displayed is not greater than 4.8 volts or less than 0.1 volt, go to next step.
Unplug A/C pressure sensor connector. Using DVOM, check voltage between sensor ground circuit and sensor 5-volt reference circuit. If voltage reading is greater than 5.5 volts, go to next step. If voltage reading is not greater than 5.5 volts, go to step 7 .
Turn ignition off. Disconnect PCM harness connectors. Turn ignition on, engine off. Using DVOM, check voltage between PCM harness connector ground and 5-volt reference "B" circuits. If voltage reading is greater than 5.5 volts, go to next step. If voltage reading is not greater than 5.5 volts, go to step 10 .
Locate and repair short to voltage in 5-volt reference "B" circuit. After repairs, go to step 13 .
If voltage reading is less than 4.5 volts, go to next step. If voltage reading is not less than 4.5 volts, go to step 9 .
Check for short to voltage in A/C pressure sensor signal circuit. Repair as necessary. After repairs, go to step 13 . If circuit is okay, go to step 10 .
Ignition off. Disconnect PCM connectors. Turn ignition on. Check 5-volt reference "B" circuit for short to ground. Repair as necessary. After repairs, go to step 13 . If circuit is okay, go to step 11 .
Turn ignition on. Ensure A/C pressure sensor is disconnected. Wait 10 seconds. Using scan tool, check if DTC P1635 is set. If DTC P1635 is set, go to next step. If DTC P1635 is not set, go to step 12 .
Replace PCM. Program replacement PCM using required equipment. After replacing PCM, go to step 13 .
Replace A/C pressure sensor. After replacing sensor, 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 this DTC. If scan tool displays that this DTC FAILED THIS IGN, return to step 2 . If scan tool does not display that this DTC FAILED THIS IGN, system is okay.

Check for faulty connections or damaged harness. Observe scan tool A/C PRESSURE display while moving harness and connectors related to A/C refrigerant pressure sensor. A change in scan tool display indicates fault location.

DTC P1639: 5-VOLT REFERENCE "B" CIRCUIT (3.8L "F" BODY)

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

PCM uses 5-volt reference "B" circuit as a sensor feed for A/C refrigerant pressure sensor. PCM monitors voltage on this circuit. If PCM senses that this voltage is out of tolerance, DTC will set.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(ref-132811-S27457185922002013000000) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Check PCM and engine grounds. Ensure grounds are clean and secure. Repair as necessary. After repairs, go to step 11 . If grounds are okay, go to next step.
Ensure that A/C is off. Using scan tool, observe A/C high side pressure. If scan tool voltage reading is greater than 4.8 volts or less than 0.1 volt, go to DTC P0530 test. If scan tool voltage reading is not greater than 4.8 volts or less than 0.1 volt, go to next step.
Disconnect A/C pressure sensor connector. Using DVOM, check voltage between sensor ground circuit and sensor 5-volt reference circuit. If voltage reading is greater than 5.5 volts, go to next step. If voltage reading is not greater than 5.5 volts, go to step 7 .
Turn ignition off. Disconnect PCM harness connector. Turn ignition on, with engine off. Using DVOM, check voltage between PCM harness connector ground and 5-volt reference "B" circuits. If voltage reading is greater than 5.5 volts, go to next step. If voltage reading is not greater than 5.5 volts, go to step 10 .
Locate and repair short to voltage in 5-volt reference "B" circuit. After repairs, go to step 11 .
If voltage reading is less than 4.5 volts, go to step 9 . If voltage reading is not less than 4.5 volts, go to next step.
Check for short to voltage in 5-volt reference "B" circuit. Repair as necessary. After repairs, go to step 11 . If circuit is okay, go to step 10 .
Turn ignition off. Disconnect PCM harness connector. Turn ignition on. Check 5-volt reference "B" circuit for short to ground. Repair as necessary. After repairs, go to step 11 . If circuit is okay, go to next step.
Replace PCM. Program replacement PCM using required equipment. After replacing PCM, 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 this DTC. If scan tool indicates that this DTC failed this ignition, return to step 2 . If scan tool does not indicate that this DTC failed this ignition, system is okay.

DTC P1639: 5-VOLT REFERENCE NO. 2 CIRCUIT (4.8L, 5.3L & 6.0L "C" & "K" SERIES)

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

PCM uses a common 5-volt reference circuit as a sensor feed to fuel tank pressure sensor and TP sensor. PCM monitors voltage on 5-volt reference circuit. If voltage is out of range, DTC will set.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(ref-132811-S27457185922002013000000) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Install scan tool. Start and operate engine at idle for 2 minutes. Using scan tool, monitor DTC. If DTCs P1635 and P1639 failed this ignition cycle, go to DTC P1635 test. If DTCs P1635 and P1639 did not fail in this ignition cycle, go to next step.
If DTC P1639 failed in this ignition cycle, go to step 5 . If DTC P1639 did not fail in this ignition cycle, go to next step.
Turn ignition off, with engine off. Using scan tool, review FREEZE FRAME and/or FAILURE RECORDS data for this DTC and observe parameters. Turn ignition off for 15 seconds, then start engine. Operate vehicle within conditions for setting this DTC. Using scan tool, select DTC option and SPECIFIC DTC option, then enter this DTC to determine if both DTCs set at the same time. If scan tool indicates that this DTC set in this ignition cycle, go to next step. If scan tool does not indicate that this DTC was set in this ignition cycle, see «DIAGNOSTIC AIDS»(/gmc/savana/i-1996-2002/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p1537-u1193) .
Turn ignition off. Disconnect PCM harness connector. Turn ignition on, with engine off. Using a test light connected to battery voltage, probe each 5-volt reference circuit at PCM harness connector for fuel tank pressure sensor and TP sensor. If test light illuminates, go to step 7 . If test light does not illuminate, go to next step.
Using DVOM, check resistance of each 5-volt reference circuit between component connector to PCM harness connector. If any of the resistance is 0-2 ohms, go to step 8 . If any of the resistance is not 0-2 ohms, go to step 9 .
Repair short to ground between fuel pump circuit and appropriate 5-volt reference circuit or signal circuit. After repairs, go to step 10 .
Replace PCM. Program replacement PCM using required equipment. After replacing PCM, go to next step.
Repair short between appropriate 5-volt reference circuit and PCM circuit that had continuity. After repairs, go to next step.
Using scan tool, select DTC, CLEAR INFO function. Start and warm engine to normal operating temperature. Select DTC, SPECIFIC, then enter this DTC. 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, repeat step 2 .
Using scan tool, select CAPTURE INFO, REVIEW INFO function. If any undiagnosed DTCs are displayed, go to applicable DTC test.

DTC P1639: 5-VOLT REFERENCE NO. 2 CIRCUIT (5.7L "F" BODY)

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

PCM uses a common 5-volt reference circuit as a sensor feed to fuel tank pressure sensor, fuel tank level sensor, and TP sensor. PCM monitors voltage on 5-volt reference circuit. If 5-volt reference circuit is out of range for greater than 2 seconds, DTC will set.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(ref-132811-S27457185922002013000000) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Start and operate engine for 2 minutes. Using scan tool, monitor DTCs. If both DTCs P1635 and P1639 failed in this ignition cycle, go to DTC P1635 test. If both DTC P1635 and P1639 did not fail in this ignition cycle, go to next step.
If only DTC P1639 failed in this ignition cycle, go to step 5 . If DTC P1639 did not fail in this ignition cycle, go to next step.
Turn ignition on, with engine off. Using scan tool, review FREEZE FRAME and/or FAILURE RECORDS data for this DTC and observe parameters. Turn ignition off for 15 seconds. Start engine. 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 option, then SPECIFIC DTC option, then enter this DTC. If scan tool indicates that this DTC failed in this ignition cycle, go to next step. If scan tool does not indicate that this DTC failed this ignition cycle, see «DIAGNOSTIC AIDS»(/gmc/savana/i-1996-2002/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p1537-u1193) .
Turn ignition off. Disconnect PCM harness connector. Using a test light connected to battery voltage, probe the 5-volt reference circuits for the A/C refrigerant pressure sensor and fuel tank pressure sensor PCM harness connector. If test light illuminates, go to step 8 . If test light does not illuminate, go to next step.
Turn ignition on, with engine off. Using test light connected to ground, probe PCM harness connector signal circuit for the A/C refrigerant pressure sensor and fuel tank pressure sensor. If test light illuminates on any of the circuits, go to step 9 . If test light does not illuminate on any of the circuits, go to next step.
Check continuity on 5-volt reference circuit and all other circuits in disconnected PCM connector. If any of the circuits indicate 0-2 ohms resistance, go to step 10 . If any of the circuit does not indicate 0-2 ohms resistance, go to step 11 .
Repair short to ground in appropriate 5-volt reference circuit. After repairs, go to step 14 .
Repair short to voltage in appropriate signal circuit. After repairs, go to step 14 .
Repair short between appropriate 5-volt reference circuit and PCM circuit that has continuity. After repairs, go to step 14 .
Reconnect PCM harness connector. Turn ignition on, engine off. Using scan tool, clear DTCs. Start and operate engine at idle. Disconnect the following components one at a time, MAP, TP, EGR, fuel level and fuel tank pressure sensors. Using scan tool, monitor DTCs. If scan tool indicates that DTC P1635/P1639 passed when components were disconnected, go to next step. If scan tool does not indicate that DTC P1635/P1639 passed when components were disconnected, go to step 13 .
Replace component which caused DTC to pass when it was disconnected. After replacing component(s), go to step 14 .
Replace PCM. Program replacement PCM using required equipment. After replacing PCM, go to next step.
Using scan tool, select DTC, CLEAR INFO function. Start and warm engine to normal operating temperature. Select DTC, SPECIFIC, then enter this DTC. 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, repeat step 2 .
Using scan tool, select CAPTURE INFO, REVIEW INFO function. If any undiagnosed DTCs are displayed, go to applicable DTC test.

DTC P1639: 5-VOLT REFERENCE NO. 2 CIRCUIT (5.7L "Y" BODY)

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

PCM uses a common 5-volt reference circuit as a sensor feed to left tank fuel level sensors. PCM monitors voltage on 5-volt reference circuit. If voltage is out of range, DTC will set.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(ref-132811-S27457185922002013000000) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Start and operate engine for 2 minutes. Using scan tool, monitor DTCs. If both DTCs P1635 and P1639 failed in this ignition cycle, diagnose affected DTC(s). If only DTC P1635 failed in this ignition cycle, go to next step.
If DTC P1639 failed in this ignition cycle, go to step 5 . If DTC P1639 did not fail in this ignition cycle, go to next step.
Turn ignition on, with engine off. Using scan tool, review FREEZE FRAME and/or FAILURE RECORDS DATA for this DTC and observe parameters. Turn ignition off for 15 seconds. Start engine. Operate vehicle within conditions required for this diagnostic to run, and as close to the conditions recorded in Freeze Frame/Failure Records as possible. Using scan tool, select DTCs option, SPECIFIC DTC option, then enter this DTC. If scan tool indicates that this DTC set in this ignition cycle, go to next step. If scan tool does not indicate that this DTC set in this ignition cycle, see «DIAGNOSTIC AIDS»(/gmc/savana/i-1996-2002/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p1537-u1193) .
Turn ignition off. Disconnect PCM harness connector. Using a test light connected to battery voltage, probe the 5-volt reference circuits for A/C refrigerant pressure sensor and fuel tank pressure sensor. If test light illuminates on any of the circuits, go to step 7 . If test light does not illuminate on any of the circuits, go to next step.
Check resistance from each 5-volt reference circuit to all other PCM circuits at PCM harness connector. If resistance on any of the circuits is 0-2 ohms, go to step 8 . If resistance on any of the circuits is not 0-2 ohms, go to step 9 .
Repair short to ground on appropriate 5-volt reference circuit. After repairs, go to step 10 .
Repair short between appropriate 5-volt reference circuit and PCM circuit that had continuity. After repairs, go to step 10 .
Replace PCM. Program replacement PCM using required equipment. After replacing PCM, go to next step.
Using scan tool, select DTC, CLEAR INFO function. Start and warm engine to normal operating temperature. Select DTC, SPECIFIC, then enter this DTC. 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, repeat step 2 .
Using scan tool, select CAPTURE INFO, REVIEW INFO function. If any undiagnosed DTCs are displayed, go to applicable DTC test.

DTC P1640 &/OR P1641: PCM OUTPUT CONTROLS FAULT-QDM "A" OUTPUT FAULTS (1.9L SATURN)

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

The Quad Driver Module (QDM) is an electronic switch which completes a ground circuit when switched on. The QDM independently controls 4 separate outputs. A load is connected between battery voltage and the QDM allowing QDM driver to control the output. Each QDM has a fault detection logic which compares its input and output voltages. The logic expects to measure less than 3 volts when the QDM is on and greater than 7 volts when off. The QDM has only one fault that will detect a fault on any of the 4 outputs. The scan tool can be used to cycle the outputs on and off. It can also perform automated test which can isolate the faulty circuit.

DTC P1640 and P1641 will set if there is an open, short to ground or short to voltage on any of the QDM output circuits, faulty SERVICE light circuit, faulty LOW COOLANT/HOT light circuit, faulty cruise clutch circuit. Fault detected for 5 seconds will set P1641. Fault detected for 20 seconds will set P1640. The QDM circuit is continuously checked when the engine is running.

Install scan tool. Perform QDM check using scan tool. If scan tool indicates that a fault is still present on any of the QDM "A" circuits, go to next step. If faults are not present, problem is intermittent. See «DIAGNOSTIC AIDS»(/gmc/savana/i-1996-2002/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p1537-u1193) .
If LOW COOLANT/HOT light and SERVICE light does not illuminate during bulb test, check affected fuses and circuit. If SERVICE light circuit is faulty, go to step 4 . If SERVICE light circuit is okay, go to next step.
Check LOW COOLANT/HOT light circuit. If circuit is okay, go to step 10 . If circuit is faulty, go to step 7 .
If SERVICE light never illuminated, go to next step. If SERVICE light stays illuminated, turn ignition off. Disconnect PCM harness connector J1 and remove SERVICE light circuit from PCM connector. Reconnect PCM harness connector. Turn ignition on. If SERVICE light illuminates, check circuit for short to ground. If circuit is okay, replace cluster assembly. If SERVICE light did not illuminate, replace PCM.
Turn ignition off. Disconnect PCM harness connector J1 and remove SERVICE light circuit from PCM connector. Using a fused jumper wire, jumper SERVICE light circuit to ground. If fuse on jumper does not blow, go to next step. If fuse on jumper blows, check circuit for short to battery voltage. If circuit is okay, replace cluster assembly.
Check if SERVICE light illuminated. If light illuminated, check for terminal tightness at PCM connector. If SERVICE light did not illuminate, check for burned out bulb, open in circuit between fuse block and PCM, or terminal tightness at harness connectors. If circuit and terminals are okay, replace cluster assembly.
If LOW COOLANT/HOT light never illuminated, go to next step. If LOW COOLANT/HOT stays illuminated, turn ignition off. Disconnect PCM harness connector J1 and remove LOW COOLANT/HOT light circuit from PCM connector. Reconnect PCM harness connector. Turn ignition on. If light illuminates, check circuit for short to ground. If circuit is okay, replace cluster assembly. If light did not illuminate, replace PCM.
Turn ignition off. Disconnect PCM harness connector J1 and remove LOW COOLANT/HOT light circuit from PCM connector. Using a fused jumper wire, jumper LOW COOLANT/HOT light circuit to ground. If fuse on jumper does not blow, go to next step. If fuse on jumper blows, check circuit for short to battery voltage. If circuit is okay, replace cluster assembly.
Check if LOW COOLANT/HOT light illuminated. If light illuminated, check for terminal tightness at PCM connector. If light did not illuminate, check for burned out bulb, open in circuit between fuse block and PCM, or terminal tightness at harness connectors. If circuit and terminals are okay, replace cluster assembly.
If scan tool QDM test indicates a fault in cruise clutch circuit, turn ignition off, then disconnect cruise control module harness connector. Turn ignition on. Check for battery voltage on cruise control module harness connector terminal No. 5. If battery voltage is present, go to next step. If battery voltage is not present, check for open in circuit or faulty cruise fuse. If fuse is blown, repair short to ground in circuit.
Using a test light connected to battery voltage, probe cruise control module harness connector terminal No. 6. If test light does not illuminate, go to next step. If test light illuminates, check circuit for short to ground or faulty PCM.
Command cruise control clutch on using scan tool. If test light illuminates when clutch is commanded on, check terminal tightness at cruise control module or faulty module. If test does not illuminate, check for open in circuit or faulty PCM.

If one output is faulty the PCM will shut down only the QDM output and not the entire quad driver, unless the quad driver reaches its thermal limit (short to voltage). At this time it will turn all 4 quad driver outputs off. When the quad driver cools down it will turn back on and this process will start over. Check 5-amp cruise fuse in the passenger compartment fuse block. Check for terminal tightness in harness connectors.

DTC P1640: DRIVER 1-INPUT VOLTAGE HIGH (4.0L "G" BODY & 4.6L "E" & "K" BODIES)

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

PCM contains Output Driver Modules (ODM) that provides 7 switchable ground outputs for operating solenoids, relays, indicator lights, and other devices. Each of these ground outputs has fault lines that feed back to the PCM's microprocessor. ODM No. 1 can also sense high voltage coming in which might damage microprocessor. DTC P1640 is used to monitor ODM No. 1 over-voltage sense line. DTC will set when over-voltage is sensed for 2 seconds.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(ref-132811-S27457185922002013000000) 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, select ENGINE 1 mode and note IGNITION 1 display. Compare this voltage reading with voltage reading displayed by vehicle message center. If PCM and vehicle voltage readings differ by greater than 1.5 volts, go to next step. If PCM and vehicle voltage readings is within 1.5 volts of each other, fault is not present. See «DIAGNOSTIC AIDS»(/gmc/savana/i-1996-2002/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p1537-u1193) .
Using DVOM, check voltage between ground and PCM fuse. If PCM fuse voltage and scan tool displayed voltage reading difference is greater than 1.5 volt, go to next step. If PCM fuse voltage and scan tool displayed voltage reading is within 1.5 volt of each other, check charging system. See appropriate GENERATORS & REGULATORS article in STARTING & CHARGING SYSTEMS.
Check for high resistance is ignition feed circuits to PCM. Repair as necessary. If circuits are okay, go to next step.
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.

An overvoltage at ODM No. 1 will also trigger DTC P0563. Use DTC P0563 to diagnose if vehicle voltage is actually too high. A loose or faulty connection at generator "L" terminal may cause DTC P1640 to set intermittently.

DTC P1641: A/C RELAY CONTROL CIRCUIT (3.1L "N" BODY & 3.4L "U" SERIES)

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

Output Driver Modules (ODMs) are used by Powertrain Control Module (PCM) to turn on current driven devices that are needed to control various engine and transaxle functions. Each ODM can control up to 7 separate outputs by grounding the device that PCM is commanding on. ODMs can diagnose each output circuit individually. DTC P1641 indicates an improper voltage level has been detected on the output circuit controlling the A/C compressor control relay.

DTC is set when ignition is on, improper voltage level detected on output circuit controlling A/C control relay and conditions are present for at least 30 seconds.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(ref-132811-S27457185922002013000000) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Turn ignition off. Disconnect PCM connector. Turn ignition on. Using DVOM, check voltage between ground and A/C relay driver circuit terminal at PCM connector. If battery voltage is present, go to next step. If battery voltage is not present, go to step 6 .
Using DVOM, set DVOM to 10-amp range. Measure current between ground and MIL driver circuit terminal at PCM connector. Monitor reading for a minimum of 2 minutes. If current is 0.1-1.5 amps, go to step 11 . If current is not 0.1-1.5 amps, go to next step.
Turn ignition off. Disconnect instrument cluster connector. Turn ignition on. Using DVOM, check voltage between ground and A/C relay driver circuit terminal at PCM connector. If voltage reading is zero volts, go to step 10 . If voltage reading is not zero volts, go to next step.
Locate and repair short to voltage in A/C relay driver circuit. After repairs, go to step 15 .
Remove and inspect fuse for A/C relay. If fuse is blown, go to next step. If fuse is okay, go to step 8 .
Locate and repair short to ground in ignition feed circuit for A/C relay. After repairs, go to step 15 .
Disconnect instrument cluster connector. Turn ignition on. Check voltage between ground and ignition feed circuit terminal for A/C relay. If battery voltage is present, go to next step. If battery voltage is not present, go to step 13 .
Check for an open or short to ground in A/C relay driver circuit. Repair as necessary. After repairs, go to step 15 . If circuit is okay, go to next step.
Check A/C relay driver circuit and ignition feed circuit for poor terminal connection at PCM connector. Repair as necessary. After repairs, go to step 15 . If connections are okay, go to step 14 .
Turn ignition off. Reconnect PCM connector. Disconnect A/C relay connector. Turn ignition on. Connect a test light between affected output driver circuit and ignition feed circuit terminals at A/C relay harness connector. Using scan tool, select OUTPUTS TEST function and cycle A/C relay on and off. If test light flashes, see «DIAGNOSTIC AIDS»(/gmc/savana/i-1996-2002/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p1537-u1193) . If test light does not flash, go to next step.
Check A/C relay driver circuit for poor terminal connection at PCM. Repair as necessary. After repairs, go to step 15 . If connection is okay, go to step 14 .
Locate and repair open in ignition feed circuit to A/C relay. After repairs, go to step 15 .
Replace PCM. Program replacement PCM using required equipment. After replacing PCM, go to next step.
Using scan tool, select CLEAR INFO or CLEAR DTCs function to 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 P1641 until DTC P1641 test runs. If scan tool indicates FAILED THIS IGN, repeat step 2 . If scan tool does not indicate FAILED THIS IGN, repair is complete.

DTC P1641: A/C RELAY CONTROL CIRCUIT (3.1L "W" BODY)

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

DTC will set when ignition is on, improper voltage level detected on output circuit controlling A/C compressor control relay and conditions are present for at least 30 seconds.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(ref-132811-S27457185922002013000000) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Turn ignition off. Disconnect PCM harness connector. Turn ignition on. Using DVOM, check voltage between ground and A/C relay control circuit terminal. If battery voltage is present, go to next step. If battery voltage is not present, go to step 6 .
Set DVOM to 10-amp range. Check current between ground and A/C relay control circuit terminal at PCM connector. Monitor reading for a minimum of 2 minutes. If current is 0.5-1.5 amps, go to next step. If current is not 0.5-1.5 amps, go to step 13 .
Turn ignition off. Reconnect PCM harness connector. Remove A/C relay. Connect a test light between A/C relay connector terminals No. 85 and 86. Turn ignition on. Using scan tool, command A/C relay on and off. If test light flashes on and off, see «DIAGNOSTIC AIDS»(/gmc/savana/i-1996-2002/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p1537-u1193) . If test light does not flash on and off, go to next step.
Check for poor connections at PCM. Repair as necessary. After repairs, go to step 22 . If connections are okay, go to step 21 .
Turn ignition off. Leave PCM connector disconnected. Remove A/C relay. Using test light connected to ground, probe relay connector terminal No. 86. If test light illuminates, go to next step. If test light does not illuminate, go to step 9 .
Check A/C relay control circuit for an open or short to ground. Repair as necessary. After repairs, go to step 22 . If circuit is okay, go to next step.
Check for poor terminal connections in A/C relay connector. Repair as necessary. After repairs, go to step 22 . If connections are okay, go to step 19 .
Turn ignition off. Remove ignition main relay. Connect test light between ground and ignition main relay connector terminal No. 87. If test light illuminates, go to next step. If test light does not illuminate, go to step 14 .
Using a fused jumper wire, jumper ignition main relay connector terminals No. 30 and 87. Connect test light between ground and A/C relay connector terminal No. 86. If test light illuminates, go to next step. If test light does not illuminate, go to step 15 .
Turn ignition on. Connect test light between ground and ignition main relay connector terminal No. 86. If test light illuminates, go to next step. If test light does not illuminate, go to step 16 .
Connect test light between battery voltage and ignition main relay connector terminal No. 85. If test light illuminates, go to step 20 . If test light does not illuminate, go to step 17 .
Turn ignition off. Leave PCM harness connector disconnected. Remove A/C relay. Connect test light between ground and A/C relay control circuit. If test light illuminates, go to step 18 . If test light does not illuminate, go to step 19 .
Locate and repair open in battery feed circuit to A/C relay connector terminal No. 87. After repairs, go to step 22 .
Locate and repair open in battery feed circuit to A/C relay connector terminal No. 86. After repairs, go to step 22 .
Locate and repair open in battery feed circuit to ignition main relay connector terminal No. 86. After repairs, go to step 22 .
Locate and repair open in ignition main relay ground circuit. After repairs, go to step 22 .
Locate and repair short to voltage in A/C relay control circuit. After repairs, go to step 22 .
Replace A/C relay. After replacing relay, go to step 22 .
Replace ignition main relay. After replacing relay, go to step 22 .
Replace PCM. Program replacement PCM using required equipment. After replacing PCM, go to next step.
Using scan tool, select CLEAR INFO or CLEAR DTCs function to 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 this DTC until DTC P1641 test runs. If scan tool indicates FAILED THIS IGN, repeat step 2 . If scan tool does not indicate FAILED THIS IGN, repair is complete.

Disconnect and inspect PCM harness connector. Inspect for damaged pins, corrosion and loose wires. 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 P1641: A/C RELAY CONTROL CIRCUIT (3.4L "N" BODY)

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

Conditions for setting DTC are: ignition is on, improper voltage level detected on output circuit controlling A/C control relay and conditions are present for at least 30 seconds.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(ref-132811-S27457185922002013000000) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Turn ignition off. Disconnect PCM harness connector. Turn ignition on. Using DVOM, check voltage between ground and A/C relay driver circuit terminal at PCM connector. If battery voltage is present, go to next step. If battery voltage is not present, go to step 6 .
Using DVOM, set DVOM to 10-amp range. Measure current between ground and MIL driver circuit. Monitor reading for at least 2 minutes. If current is 0.1-1.5 amps, go to step 11 . If current is not 0.1-1.5 amps, go to next step.
Turn ignition off. Disconnect A/C relay. Using DVOM, check voltage between ground and A/C relay driver circuit. If voltage reading is zero volts, go to step 14 . If voltage reading is not zero volts, go to next step.
Locate and repair short to voltage in A/C relay driver circuit. After repairs, go to step 16 .
Remove and inspect fuse for A/C relay. If fuse is blown, go to next step. If fuse is okay, go to next step. If fuse is okay, go to step 8 .
Locate and repair short to ground in ignition feed circuit for A/C relay. After repairs, go to step 16 .
Disconnect A/C relay. Turn ignition on. Check voltage between ground and A/C relay ignition feed circuit. If battery voltage is present, go to next step. If battery voltage is not present, go to step 13 .
Check for an open or short to ground in A/C relay driver circuit. Repair as necessary. After repairs, go to step 16 . If circuit is okay, go to next step.
Check A/C relay driver circuit and ignition feed circuit for poor terminal connection at PCM connector. Repair as necessary. After repairs, go to step 16 . If connections are okay, go to step 14 .
Turn ignition off. Reconnect PCM harness connector. Disconnect A/C relay connector. Turn ignition on. Connect a test light between affected output driver circuit and ignition feed circuit terminals at A/C relay harness connector. Using scan tool, select OUTPUTS TEST function and cycle A/C relay on and off. If test light flashes, see «DIAGNOSTIC AIDS»(/gmc/savana/i-1996-2002/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p1537-u1193) . If test light does not flash, go to next step.
Check A/C relay driver circuit for poor terminal connection at PCM. Repair as necessary. After repairs, go to step 16 . If connection is okay, go to step 15 .
Locate and repair open in ignition feed circuit to A/C relay. After repairs, go to step 16 .
Replace A/C relay. After replacing relay, go to step 16 .
Replace PCM. Program replacement PCM using required equipment. After replacing PCM, go to next step.
Using scan tool, select CLEAR INFO or CLEAR DTCs function to 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 this DTC until DTC test runs. If scan tool indicates FAILED THIS IGN, repeat step 2 . If scan tool does not indicate FAILED THIS IGN, repair is complete.

DTC P1641: A/C RELAY CONTROL CIRCUIT (3.8L "C", "G", "H" & "W" BODIES)

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

Output Driver Modules (ODM) are used by the PCM to turn on current-driven devices needed to control various engine and transaxle functions. Each ODM can control up to 7 output by supplying ground to the device PCM is commanding on. ODMs can diagnose each circuit individually. DTC will set when ODM detects an improper voltage level.

Conditions required to set DTC are, ignition is on, an improper voltage level has been detected on output circuit controlling A/C compressor control relay and condition is present longer than 30 seconds.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(ref-132811-S27457185922002013000000) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Turn ignition off. Disconnect PCM harness connectors. Turn ignition on. Using a DVOM, check voltage between engine ground and PCM harness connector A/C compressor control relay control circuit. If battery voltage is present, go to next step. If battery voltage is not present, go to step 6 .
Using DVOM in 10-amp scale, check current between engine ground and A/C compressor control relay control circuit for 2 minutes. If current remains at 0.05-0.50 amp, go to step 11 . If current does not remain at 0.05-0.50 amp, go to next step.
Turn ignition off. Disconnect PCM harness connector and A/C compressor control relay connector. Turn ignition on. Using DVOM, check voltage between engine ground and A/C relay control driver circuit. If voltage reading is zero volts, go to step 10 . If voltage reading is not zero volts, go to next step.
Locate and repair short to voltage in A/C compressor control relay control circuit. After repairs, go to step 16 .
Check ignition feed fuse for A/C compressor control relay. If fuse is blown, go to next step. If fuse is okay, go to step 8 .
Locate and repair short to ground in ignition feed circuit for A/C compressor control relay. Replace fuse. After repairs, go to step 16 .
Disconnect A/C compressor control relay. Turn ignition on. Check voltage between engine ground and A/C compressor control relay ignition feed circuit. If battery voltage is present, go to next step. If battery voltage is not present, go to step 13 .
Check A/C compressor control relay circuit for open or short to ground. If a problem is found, repair as necessary. After repairs, go to step 16 . If circuit is okay, go to next step.
Check A/C compressor control relay circuits for faulty connection at PCM or faulty connection at relay connector. Repair as necessary. After repairs, go to step 16 . If connection is okay, go to step 14 .
Turn ignition off. Reconnect A/C compressor clutch and PCM connectors. Disconnect A/C compressor control relay connector. Turn ignition on. Connect a test light between A/C compressor control relay connector and ignition feed circuits at relay connector. Using scan tool, cycle A/C compressor control relay on and off. If test light flashes on and off, see «DIAGNOSTIC AIDS»(/gmc/savana/i-1996-2002/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p1537-u1193) . If test light does not flash on and off, go to next step.
Check A/C compressor control relay control circuit for faulty connection at PCM. Repair as necessary. After repairs, go to step 16 . If connection is okay, go to step 15 .
Locate and repair open ignition feed circuit to A/C compressor control relay. After repairs, go to step 16 .
Replace A/C compressor control relay. After replacing relay, go to step 16 .
Replace PCM. Program replacement PCM using required equipment. After replacing PCM, 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 this DTC. If scan tool displays that this DTC FAILED THIS IGN, return to step 2 . If scan tool does not display that this DTC FAILED THIS IGN, repair is complete.

Check for faulty connections or damaged harness. Disconnect PCM connector. Turn ignition on. Connect a DVOM between engine ground and PCM harness connector MIL driver circuit. Observe DVOM while moving all related harness and connectors. A change in voltage display indicates fault location.

DTC P1641: MALFUNCTION INDICATOR LIGHT (MIL) CONTROL CIRCUIT (4.0L "G" BODY & 4.6L "E" & "K" BODIES)

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

PCM contains Output Driver Modules (ODM) that provides 7 switchable ground outputs for operating solenoids, relays, indicator lights, and other devices. Each of these ground outputs has fault lines that feed back to the PCM's microprocessor. When the output is off, the output driver should receive the 12 volts fed to the solenoid, relay, etc. When the output is on, it should receive zero volts, since it is grounding the output. When PCM sees zero volts when the output is off or 12 volts when the output is on, it sets a fault line low. DTC P1641 is used to monitor the fault line of the SERVICE ENGINE SOON light.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(ref-132811-S27457185922002013000000) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Turn ignition on. Check if MIL illuminates after 5 seconds. If MIL illuminates, go to next step. If MIL does not illuminate, go to step 4 .
Using scan tool, enter OUTPUT TESTS then select MIL. Command MIL off. If MIL turns off, fault is not present. See «DIAGNOSTIC AIDS»(/gmc/savana/i-1996-2002/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p1537-u1193) . If MIL does not turn off, go to step 8 .
Select ENGINE 3 mode and note MALFUNCTION IND LAMP DRIVER display on scan tool. If scan tool display indicates OK, go to next step. If scan tool display does not indicate OK, go to step 6 .
Store fluid life index as indicated on scan tool. Turn ignition off and wait 30 seconds, then disconnect PCM harness connector C2. Remove IP cluster fuse. Turn ignition on. Using DVOM, check voltage between ground and MIL signal circuit at PCM harness connector C2. If voltage reading is.5 volt or greater, go to step 9 . If voltage reading is not.5 volt or greater, go to step 13 .
Reinstall IP cluster fuse. Using a jumper wire, jumper MIL signal circuit at PCM harness connector C2 to ground. If MIL illuminates, go to step 13 . If MIL does not illuminate, go to next step.
Check condition of IP fuse. If fuse is faulty, go to step 10 . If fuse is okay, go to step 13 .
Store fluid life index as indicated on scan tool. Turn ignition off and wait 30 seconds, then disconnect PCM harness connector C2. Turn ignition on. If MIL illuminates, go to step 12 . If MIL does not illuminate, go to step 13 .
Repair short to voltage in MIL signal circuit.
Repair short to ground in circuit between MIL and fuse block.
Repair open in MIL circuit from fuse block to PCM. Check for faulty MIL bulb.
Replace short to ground in MIL circuit between MIL bulb and PCM.
Check terminal contact at PCM harness connector C2. Repair as necessary. If terminal connector is okay, go to next step.
Replace PCM. Program replacement PCM using required equipment.

Use the FAILURE REC as indicated on scan tool to aid in diagnosing an intermittent fault. Use data captured when DTC was set, to determine if an open or shorted condition caused the DTC to set. Ensure no other DTCs are present, commanding MIL to illuminate.

DTC P1642: VEHICLE SPEED OUTPUT CIRCUIT (4.0L "G" BODY & 4.6L "E" & "K" BODIES)

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

PCM contains Output Driver Modules (ODMs) that provides 7 switchable ground outputs for operating solenoids, relays, indicator lights, and other devices. Each of these ground outputs has fault lines that feed back to the PCM's microprocessor. When the output is off, the output driver should receive the 12 volts fed to the solenoid, relay, etc. When the output is on, it should receive zero volts, since it is grounding the output. If PCM sees zero volts when the output is off or 12 volts when the output is on, it sets a fault line low.

DTC P1642 is used to monitor the fault line of the vehicle speed output signal. The instrument panel cluster sends 12 volts to PCM. The PCM then sends a PWM signal that the IPC, cruise control module and Remote Accessory Control (RAC) module use to determine vehicle speed.

DTC will set when DTC P1640 is not set, engine running for at least 10 seconds and fault line is low for 2 seconds.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(ref-132811-S27457185922002013000000) 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, select Vehicle Speed Output Signal display. If scan tool display indicates OK, go to next step. If scan tool display does not indicate OK, go to step 6 .
Start engine. Raise vehicle wheels off the ground. Using scan tool, check if wheels are generating a vehicle speed signal. If scan tool indicates OPEN/SHORT, go to next step. If scan tool does not indicate OPEN/SHORT, fault is not present. See «DIAGNOSTIC AIDS»(/gmc/savana/i-1996-2002/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p1537-u1193) .
Using scan tool record fluid life index. Turn ignition off. Wait 30 seconds then disconnect PCM harness connector. Turn ignition on, engine off. Using DVOM, check voltage between ground and PCM harness connector terminal No. 25. If voltage reading is 10 volts or greater, go to step 7 . If voltage reading is not 10 volts or greater, go to next step.
Repair open or short to ground in vehicle speed output circuit.
Repair short to voltage in vehicle speed output circuit.
Check terminal contact at PCM. Repair as necessary. If terminal contact is okay, go to next step.
Replace PCM. Program replacement PCM using required equipment.

Review FAILURE RECORDS to help diagnose an intermittent Diagnostic Aids.

Use the FAILURE REC indicated on scan tool to aid in diagnosing an intermittent fault. Use data captured when DTC was set to determine the conditions under which DTC set.

DTC P1644: DELIVERED TORQUE OUTPUT CIRCUIT (4.0L "G" BODY & 4.6L "E" & "K" BODIES)

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

DTC P1644 is used to monitor the fault line of the delivered torque output to the EBTCM. The EBTCM sends ignition voltage on the delivered torque PWM output circuit to the PCM. The PCM will then rapidly pulse this circuit to ground creating a Pulse Width Modulated (PWM) signal, indicating the percentage of torque output the engine is producing. The EBTCM uses this PWM signal for traction control.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(ref-132811-S27457185922002013000000) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Turn ignition on. Using scan tool in ENGINE 3 mode, observe DELIVERED TORQUE DRIVER display. If scan tool display indicates OK, fault is not present. See «DIAGNOSTIC AIDS»(/gmc/savana/i-1996-2002/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p1537-u1193) . If scan tool display does not indicate OK, go to next step.
If scan tool display indicates OPEN, go to next step. If scan tool display does not indicate OPEN, go to step 6 .
Store fluid life index as indicated on scan tool. Turn ignition off and wait 30 seconds, then disconnect PCM harness connector C2. Turn ignition on. Using DVOM, check voltage between ground and delivered torque PWM output circuit at PCM harness connector C2. If voltage reading is 10 volts or greater, go to step 13 . If voltage reading is not 10 volts or greater, go to next step.
Turn ignition to LOCK position. Disconnect EBTCM harness connector. Check resistance of delivered torque PWM output circuit between PCM harness connector and EBTCM harness connector terminals. If resistance is 5 ohms or less, go to step 12 . If resistance is not 5 ohms or less, go to step 9 .
Turn ignition to LOCK position. Disconnect EBTCM harness connector. Turn ignition on. If scan tool display indicates OPEN, go to step 12 . If scan tool display does not indicate OPEN, go to next step.
Store fluid life index as indicated on scan tool. Turn ignition off and wait 30 seconds, then disconnect PCM harness connector C2. Turn ignition on. Using DVOM, check resistance between ground and delivered torque PWM output circuit at PCM harness connector C2 terminal. If voltage reading is greater than.5 volt, go to step 10 . If voltage reading is not greater than.5 volt, go to next step.
Using DVOM, check resistance between ground and delivered torque PWM output circuit at PCM harness connector C2 terminal. If resistance is 10,000 ohms or greater, go to step 13 . If resistance is not 10,000 ohms or greater, go to step 11 .
Repair open in delivered torque PWM output circuit.
Repair short to voltage in delivered torque PWM output circuit.
Repair short to ground in delivered torque PWM output circuit.
Fault is in the EBTCM system. Diagnose EBTCM. See appropriate ANTI-LOCK article in BRAKES. If fault is not found in EBTCM system, check for faulty terminal contact to EBTCM. If terminal contact is okay, replace EBTCM.
Check terminal contact at PCM harness connector C2. Repair as necessary. If terminal contact is okay, go to next step.
Replace PCM. Program replacement PCM using required equipment.

Check for an intermittent poor connection at both the PCM and EBTCM. Also, check for open or short in delivered torque PWM output circuit between EBTCM and PCM.

DTC P1645: EVAP PURGE SOLENOID OUTPUT CIRCUIT (4.0L "G" BODY & 4.6L "E" & "K" BODIES)

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

PCM contains Output Driver Modules (ODM) that provides 7 switchable ground outputs for operating solenoids, relays, indicator lights, and other devices. Each of these ground outputs has fault lines that feed back to the PCM's microprocessor. When the output is off, the output driver should receive the 12 volts fed to the solenoid, relay, etc. When the output is on, it should receive zero volts, since it is grounding the output. If PCM sees zero volts when the output is off or 12 volts when the output is on, it sets a fault line low. DTC is used to monitor the fault line of the EVAP control solenoid.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(ref-132811-S27457185922002013000000) 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 DTC P1633 or P1644 is present. If any of the DTC is present, diagnose affected DTC first. If DTC P1653 or P1644 is not present, go to next step.
If DTC P0102, P0401, P0550, P0753, P0758, P1406 or P1860 is also present, go to step 10 . If these DTCs are not present, go to next step.
Using scan tool, select ENGINE 3 and note EVAP PURGE SOL. DRIVER display. If scan tool display indicates OK, go to next step. If scan tool display does not indicate OK, go to step 6 .
Start and idle engine. Select OUTPUT TESTS and select EVAP PURGE. Command EVAP purge solenoid on (open) for at least 2 seconds. Note EVAP PURGE SOL. DRIVER display. If scan tool display indicates OK, fault is not present. See «DIAGNOSTIC AIDS»(/gmc/savana/i-1996-2002/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p1537-u1193) . If scan tool display does not indicate OK, go to step 9 .
Store fluid life index as indicated on scan tool. Turn ignition off and wait 30 seconds, then disconnect PCM harness connector C2. Turn ignition on. Using DVOM, check voltage between ground and EVAP purge solenoid circuit at PCM harness connector C2. If voltage reading is 10 volts or greater, go to step 15 . If voltage reading is not 10 volts or greater, go to next step.
Disconnect EVAP purge solenoid harness connector. Check voltage between ground and EVAP purge solenoid ignition circuit harness connector terminal. If voltage reading is 10 volts or greater, go to next step. If voltage reading is not 10 volts or greater, go to step 11 .
Using jumper wire, jumper EVAP purge solenoid harness connector terminals together. Check voltage between ground and EVAP purge solenoid circuit at PCM harness connector terminal. If voltage reading is 10 volts or greater, go to step 12 . If voltage reading is not 10 volts or greater, go to step 13 .
Turn ignition off. Disconnect EVAP purge solenoid harness connector. Turn ignition on. Using DVOM, check voltage between ground and EVAP purge solenoid signal circuit harness connector terminal. If voltage reading is.5 volt or greater, go to step 14 . If voltage reading is not.5 volt or greater, go to step 12 .
Repair open or short in EVAP purge solenoid ignition circuit. Also, check for faulty fuse. Repair as necessary.
Repair open in EVAP purge solenoid ignition circuit and splice.
Replace EVAP purge solenoid.
Repair open in circuit between EVAP purge solenoid and PCM.
Repair short to voltage in circuit between EVAP purge solenoid and PCM.
Check terminal contact at PCM harness connector C2. Repair as necessary. If terminal contact is okay, go to next step.
Replace PCM. Program replacement PCM using required equipment.

Use the FAILURE REC. on scan tool to aid in diagnosing an intermittent fault. Use the data captured when the DTC set, to determine if an open or shorted condition caused the DTC to set.

DTC P1646: BOOST CONTROL SOLENOID CONTROL CIRCUIT (3.8L "C", "G", "H" & "W" BODIES)

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

Output Driver Modules (ODM) are used by PCM to turn on current-driven devices needed to control various engine and transaxle functions. Each ODM can control up to 7 outputs, including boost control solenoid, by supplying ground to device PCM is commanding on. ODMs can diagnose each circuit individually. If ODM "A" output 5 (boost control solenoid driver circuit) detects an improper voltage level, DTC is set.

Conditions for setting DTC are: ignition is on, an improper voltage level has been detected on boost control solenoid driver circuit and conditions are present for at least 30 seconds.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(ref-132811-S27457185922002013000000) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Turn ignition off. Disconnect PCM harness connector. Turn ignition on. Using a DVOM, check voltage between engine ground and PCM harness connector boost control solenoid driver circuit. If battery voltage is present, go to next step. If battery voltage is not present, go to step 6 .
Using DVOM in 10-amp scale, check current between engine ground and boost control solenoid driver circuit for 2 minutes. If current remains.05-.80 amp go to step 11 . If current does not remain between.05-.80 amp, go to next step.
Turn ignition off. Leave PCM harness connector disconnected. Disconnect boost control solenoid connector. Turn ignition on. Using DVOM, check voltage between engine ground and boost control solenoid driver circuit. If voltage reading is zero volts, go to step 10 . If voltage reading is not zero volts, go to next step.
Locate and repair short to voltage in boost control solenoid driver circuit. After repairs, go to step 16 .
Check boost control solenoid ignition feed fuse. If fuse is blown, go to next step. If fuse is okay, go to step 8 .
Locate and repair short to ground in boost control solenoid ignition feed circuit. Replace fuse. After repairs, go to step 16 .
Disconnect boost control solenoid connector. Turn ignition on. Check voltage between engine ground and boost control solenoid ignition feed circuit. If battery voltage is present, go to next step. If battery voltage is not present, go to step 13 .
Check boost control solenoid driver circuit for open or short to ground. Repair as necessary. After repairs, go to step 16 . If circuit is okay, go to next step.
Check boost control solenoid driver and boost control solenoid ignition feed circuits for faulty connection at PCM. Repair as necessary. After repairs, go to step 16 . If connection is okay, go to step 14 .
Turn ignition off. Reconnect PCM harness connector. Disconnect boost control solenoid connector. Turn ignition on. Connect a test light between boost control solenoid harness connector boost control solenoid driver and ignition feed circuits. Using scan tool, cycle boost control solenoid on and off. If test light flashes on and off, see «DIAGNOSTIC AIDS»(/gmc/savana/i-1996-2002/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p1537-u1193) . If test light does not flash on and off, go to next step.
Check boost control solenoid driver circuit for faulty connection at PCM. Repair as necessary. After repairs, go to step 16 . If connection is okay, go to step 15 .
Locate and repair open boost control solenoid ignition feed circuit. After repairs, go to step 16 .
Replace boost control solenoid. After replacing boost control solenoid, go to step 16 .
Replace PCM. Program replacement PCM using required equipment. After replacing PCM, 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 this DTC. If scan tool displays that this DTC FAILED THIS IGN, return to step 2 . If scan tool does not display that this DTC FAILED THIS IGN, repair is complete.

Check for faulty connections or damaged harness. Disconnect PCM connector. Turn ignition on. Connect a DVOM between engine ground and PCM harness connector boost control solenoid driver circuit. Observe DVOM while moving all related harness and connectors. A change in voltage display indicates fault location.

DTC P1646: EVAP VENT VALVE OUTPUT CIRCUIT (4.0L "G" BODY & 4.6L "E" & "K" BODIES)

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

PCM contains Output Driver Modules (ODM) that provides 7 switchable ground outputs for operating solenoids, relays, indicator lights, and other devices. Each of these ground outputs has fault lines that feed back to the PCM's microprocessor. When output is off, the output driver should receive the 12 volts fed to the solenoid, relay, etc. When output is on, it should receive zero volts, since it is grounding the output. If PCM sees zero volts when output is off or 12 volts when output is on, it sets a fault line low. DTC is used to monitor the fault line of the EVAP control solenoid.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(ref-132811-S27457185922002013000000) 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 DTC P1633 or P1634 is present. If any of the DTC is present, diagnose affected DTC first. If DTC P1633 or P1634 is not present, go to next step.
Using scan tool, view EVAP vent valve driver display. If scan tool displays OK, go to next step. If scan tool does not display OK, go to step 5 .
Select OUTPUT TESTS and select EVAP VENT VALVE. Command EVAP vent valve on (open) for at least 2 seconds. Note EVAP vent valve display. If scan tool display indicates OK, fault is not present. See «DIAGNOSTIC AIDS»(/gmc/savana/i-1996-2002/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p1537-u1193) . If scan tool display does not indicate OK, go to step 8 .
Record fluid life index as indicated on scan tool. Turn ignition off. Wait 30 seconds, then disconnect PCM harness connector C2. Turn ignition on. Using DVOM, check voltage between ground and EVAP vent valve circuit at PCM harness connector C2. If voltage reading is 10 volts or greater, go to step 13 . If voltage reading is not 10 volts or greater, go to next step.
Disconnect EVAP vent valve harness connector. Check voltage between ground and EVAP vent valve connector terminal "A". If voltage reading is 10 volts or greater, go to next step. If voltage reading is not 10 volts or greater, go to step 12 .
Using jumper wire, jumper EVAP vent valve harness connector terminals together. Check voltage between ground and PCM harness connector terminal No. 29. If voltage reading is 10 volts or greater, go to step 9 . If voltage reading is not 10 volts or greater, go to step 10 .
Turn ignition off. Disconnect EVAP vent valve harness connector. Turn ignition on. Using DVOM, check voltage between ground and EVAP vent valve harness connector terminal "B". If voltage reading is.5 volt or greater, go to step 11 . If voltage reading is not.5 volt or greater, go to step 13 .
Replace EVAP purge solenoid.
Repair open or short to ground in EVAP vent valve circuit between vent valve and PCM.
Repair short to voltage in EVAP vent valve input circuit between vent valve and PCM.
Check for open in EVAP vent valve power feed circuit. Check for short to ground (blown fuse) in EVAP vent valve power feed circuit. Check for shorted EVAP vent valve (if fuse is blown).
Check terminal contact at PCM harness connector C2. Repair as necessary. If terminal contact is okay, go to next step.
Replace PCM. Program replacement PCM using required equipment.

Use the FAILURE REC. on scan tool to aid in diagnosing an intermittent fault. Use the data captured when the DTC set, to determine if an open or shorted condition caused the DTC to set.

DTC P1650 &/OR P1651: PCM OUTPUT CONTROLS FAULT - QDM "B" OUTPUT FAULTS (1.9L SATURN)

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

DTC P1650 and P1651 will set if there is an open, short to ground or short to voltage on any of the QDM output circuits, faulty MIL circuit, faulty upshift light circuit, faulty cooling fan relay circuit or A/C relay circuit. Fault detected for 5 seconds will set P1651. Fault detected for 20 seconds will set P1650. The QDM circuit is continuously checked when the engine is running.

Install scan tool and perform QDM test. If test indicates a fault is still present on any of the QDM "B" circuits, go to next step. If fault is not present, problem is intermittent. See «DIAGNOSTIC AIDS»(/gmc/savana/i-1996-2002/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p1537-u1193) .
If MIL circuit is not faulty, go to step 7 . If MIL circuit is faulty, perform bulb test. MIL should blink on and off, then stay on when ignition is turned on. If MIL never illuminated, go to step 4 . If MIL stays on, go to next step.
Turn ignition off. Disconnect PCM harness connector J1 and remove MIL circuit from harness connector. Reconnect PCM harness connector. Turn ignition on. If MIL does not illuminate, replace PCM. If MIL illuminates, check circuit for short to ground. If circuit is okay, replace cluster assembly.
Turn ignition off. Disconnect PCM harness connector J1 and remove MIL circuit from harness connector. Reconnect PCM connector. Turn ignition on. Using a fused jumper, jumper MIL circuit to ground. If fuse in jumper does not blow, go to next step. If fuse in jumper blows, repair short in circuit. If circuit is okay, replace cluster assembly.
If MIL illuminates, check for terminal tightness of faulty PCM. If MIL does not illuminate, check burned out bulb, open in MIL circuit between fuse block and PCM or check for terminal tightness. If circuits and terminals are okay, replace cluster assembly.
Check UPSHIFT light circuit. If circuit is okay, go to step 10 . If circuit is faulty, perform bulb test. If UPSHIFT light never illuminated, go to step 8 . If UPSHIFT light stays on, go to next step.
Turn ignition off. Disconnect PCM harness connector J1 and remove UPSHIFT circuit from harness connector. Reconnect PCM harness connector. Turn ignition on. If UPSHIFT light does not illuminate, replace PCM. If UPSHIFT light illuminates, check circuit for short to ground. If circuit is okay, replace cluster assembly.
Turn ignition off. Disconnect PCM harness connector J1 and remove UPSHIFT light circuit from harness connector. Reconnect PCM harness connector. Turn ignition on. Using a fused jumper, jumper UPSHIFT light circuit to ground. If fuse in jumper does not blow, go to next step. If fuse in jumper blows, repair short in circuit. If circuit is okay, replace cluster assembly.
If UPSHIFT light illuminates, check for terminal tightness of faulty PCM. If MIL does not illuminate, check burned out bulb, open in UPSHIFT light circuit between fuse block and PCM or check for terminal tightness. If circuits and terminals are okay, replace cluster assembly.
Check if cooling fan relay circuit is faulty. If cooling fan relay circuit is not faulty go to step 14 . If cooling fan relay is faulty, check 30-amp cooling fan relay fuse. Replace as necessary. Retest by removing cooling fan relay and substitute relay with A/C relay. If cooling fan now operates, check for terminal tightness or faulty cooling fan relay. If cooling fan does not operate, go to next step.
Remove A/C relay from cooling fan relay slot. Check voltage on cooling fan relay circuit to PCM. If voltage is present, repair for short to voltage in circuit. If voltage is not present, go to next step.
Check for voltage between battery and cooling fan relay. If battery voltage is present, go to next step. If battery voltage is not present, check for open or short to ground in circuit.
Using a test light connected to battery voltage, probe cooling fan relay terminal C10. If test light illuminates, check circuit for short to ground of faulty PCM. If test light does not illuminate, check for open in circuit between relay and PCM. If circuit is okay, replace PCM.
If scan tool QDM test indicates fault in A/C relay circuit, remove A/C relay and substitute with cooling fan relay. Repeat scan tool QDM test. If A/C relay test passes, check for terminal tightness or faulty A/C relay. If A/C relay test does not pass, go to next step.
Remove cooling fan relay from A/C relay slot. Check voltage on A/C relay circuit to PCM. If voltage is present, check for short to voltage in circuit to PCM. If voltage is not present, check voltage in circuit between fuse block and A/C relay. If voltage is present, go to next step. If voltage is not present, repair open or short to ground in circuit.
Using a test light connected to battery voltage, probe A/C relay circuit to PCM. If test light illuminates, circuit is shorted to ground or PCM is faulty. If test light does not illuminate, check open in circuit to PCM or faulty PCM.

If one output is faulty the PCM will shut down only the QDM output and not the entire quad driver, unless the quad driver reaches its thermal limit (short to voltage). At this time it will turn all 4 quad driver outputs off. When the quad driver cools down it will turn back on and this process will start over. Check related fuses in the passenger compartment fuse block. Check relay resistance. Resistance should be 70-90 ohms. A shorted or open relay or bulb can cause DTC to set. Check for terminal tightness in harness connectors.

DTC P1650: CONTROL MODULE OUTPUT "B" CIRCUIT (4.0L "G" BODY & 4.6L "E" & "K" BODIES)

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

PCM contains Output Driver Modules (ODMs) that provides 7 switchable ground outputs for operating solenoids, relays, indicator lights, and other devices. Each of these ground outputs has fault lines that feed back to the PCM's microprocessor. ODM No. 2 can also sense high voltage coming in which might damage the microprocessor. DTC P1650 is used to monitor ODM No. 2 overvoltage sense line. DTC will set when over-voltage is sensed for 2 seconds.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(ref-132811-S27457185922002013000000) 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, select ENGINE 1 mode and note IGNITION 1 display. Compare this voltage reading with voltage reading displayed by vehicle message center. If PCM and vehicle voltage readings differ by greater than 1.5 volts, go to next step. If PCM and vehicle voltage readings are within 1.5 volts of each other, fault is not present. See «DIAGNOSTIC AIDS»(/gmc/savana/i-1996-2002/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p1537-u1193) .
Using DVOM, check voltage between ground and PCM fuse. If PCM fuse voltage and scan tool displayed voltage reading difference is greater than 1.5 volts, go to next step. If PCM fuse voltage and scan tool displayed voltage reading are within 1.5 volts of each other, check charging system. See appropriate GENERATORS & REGULATORS article in STARTING & CHARGING SYSTEMS.
Check for high resistance in ignition feed circuits to PCM. Repair as necessary. If circuits are okay, go to next step.
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.

An overvoltage at ODM No. 2 will also trigger DTC P0563. Use DTC P0563 to diagnose if vehicle voltage is actually too high. A loose or faulty connection at generator "L" terminal may cause DTC P1650 to set intermittently.

DTC P1651: FAN 1 RELAY CONTROL CIRCUIT (3.1L "N" & "W" BODIES & 3.4L "N" BODY)

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

Output Driver Modules (ODM) are used by PCM to turn on current-driven devices needed to control various engine and transaxle functions. Each ODM can control up to 7 outputs, including fan 1 relay, by supplying ground to device PCM is commanding on. ODMs can diagnose each circuit individually. If ODM "B" output 1 (fan 1 relay driver circuit) detects an improper voltage level, P1651 is set.

Conditions required to set DTC are, ignition is on, an improper voltage level detected on fan 1 relay driver circuit and condition present for at least 30 seconds.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(ref-132811-S27457185922002013000000) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Turn ignition off. Disconnect PCM harness connector. Turn ignition on. Using a DVOM, check voltage between engine ground and PCM harness connector fan 1 relay driver circuit. If voltage is about battery voltage, go to next step. If voltage is not about battery voltage, go to step 6 .
Using DVOM in 10-amp scale, check current between engine ground and fan 1 relay driver circuit for 2 minutes. If current remains 0.1-1.5 amps go to step 11 . If current does not remain 0.1-1.5 amps, go to next step.
Turn ignition off. Disconnect PCM harness connector. Disconnect fan 1 relay connector. Turn ignition on. Using DVOM, check voltage between engine ground and fan 1 relay driver circuit. If voltage reading is zero volts, go to step 10 . If voltage reading is not zero volts, go to next step.
Locate and repair short to voltage in fan 1 relay driver circuit. After repairs, go to step 16 .
Check fan 1 relay ignition feed fuse. If fuse is blown, go to next step. If fuse is okay, go to step 8 .
Locate and repair short to ground in fan 1 relay ignition feed circuit. Replace fuse. After replacing fuse, go to step 16 .
Disconnect fan 1 relay connector. Turn ignition on. Check voltage between engine ground and fan 1 relay ignition feed circuit. If voltage is near battery voltage, go to next step. If voltage is not near battery voltage, go to step 13 .
Check fan 1 relay driver circuit for open or short to ground. If a problem is found, repair as necessary. After repairs, go to step 16 . If no problem is found, go to next step.
Check fan 1 relay driver and fan 1 relay ignition feed circuits for faulty connection at PCM. If faulty connection is found, repair as necessary. After repairs, go to step 16 . If connection is okay, go to step 14 .
Turn ignition off. Reconnect PCM connectors. Disconnect fan 1 relay connector. Turn ignition on. Connect a test light between fan 1 relay harness connector fan 1 relay driver and ignition feed circuits. Using scan tool, cycle fan 1 relay on and off. If test light flashes on and off, go to «DIAGNOSTIC AIDS»(/gmc/savana/i-1996-2002/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p1537-u1193) . If test light does not flash on and off, go to next step.
Check fan 1 relay driver circuit for faulty connection at PCM. If faulty connection is found, repair as necessary. After repairs, go to step 16 . If connection is okay, go to step 15 .
Locate and repair open fan 1 relay ignition feed circuit. After repairs, go to step 16 .
Replace fan 1 relay. After replacing relay, go to step 16 .
Replace PCM. Program replacement PCM using required equipment. After replacing PCM, 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 this DTC. If scan tool displays that this DTC FAILED THIS IGN, return to step 2 . If scan tool does not display that this DTC FAILED THIS IGN, repair is complete.

Check for faulty connections or damaged harness. Disconnect PCM connector. Turn ignition on. Connect a DVOM between engine ground and PCM harness connector fan 1 relay driver circuit. Observe DVOM while moving all related harness and connectors. A change in voltage display indicates fault location.

DTC P1651: FAN 1 RELAY CONTROL CIRCUIT (3.8L "C", "G", "H" & "W" BODIES)

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

Conditions required to set DTC are, ignition is on, an improper voltage level has been detected on fan 1 relay driver circuit and conditions are present for at least 30 seconds.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(ref-132811-S27457185922002013000000) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Turn ignition off. Disconnect PCM connectors. Turn ignition on. Using a DVOM, check voltage between engine ground and PCM harness connector fan 1 relay driver circuit. If battery voltage is present, go to next step. If battery voltage is not present, go to step 6 .
Disconnect cooling fans. Using DVOM in 10-amp scale, check current between engine ground and fan 1 relay driver circuit for 2 minutes. If current remains.05-.50 amp, go to step 11 . If current does not remain between.05-.50 amp, go to next step.
Turn ignition off. Reconnect cooling fans. With PCM connectors still disconnected, disconnect fan 1 relay connector. Turn ignition on. Using DVOM, check voltage between engine ground and fan 1 relay driver circuit. If voltage is zero volts, go to step 10 . If voltage is not zero volts, go to next step.
Locate and repair short to voltage in fan 1 relay driver circuit. After repairs, go to step 16 .
Check fan 1 relay ignition feed fuse. If fuse is blown, go to next step. If fuse is okay, go to step 8 .
Locate and repair short to ground in fan 1 relay ignition feed circuit. Replace fuse. After repairs, go to step 16 .
Disconnect fan 1 relay connector. Turn ignition on. Check voltage between engine ground and fan 1 relay ignition feed circuit. If battery voltage is present, go to next step. If battery voltage is not present, go to step 13 .
Check fan 1 relay driver circuit for open or short to ground. Repair as necessary. After repairs, go to step 16 . If circuit is okay, go to next step.
Check fan 1 relay driver and fan 1 relay ignition feed circuits for faulty connection at PCM. Repair as necessary. After repairs, go to step 16 . If connection is okay, go to step 14 .
Turn ignition off. Reconnect PCM harness connectors. Disconnect fan 1 relay connector. Turn ignition on. Connect a test light between fan 1 relay harness connector fan 1 relay driver and ignition feed circuits. Using scan tool, cycle fan 1 relay on and off. If test light flashes on and off, see «DIAGNOSTIC AIDS»(/gmc/savana/i-1996-2002/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p1537-u1193) . If test light does not flash on and off, go to next step.
Check fan 1 relay driver circuit for faulty connection at PCM. Repair as necessary. After repairs, go to step 16 . If connection is okay, go to step 15 .
Locate and repair open fan 1 relay ignition feed circuit. After repairs, and go to step 16 .
Replace fan 1 relay. After replacing relay, go to step 16 .
Replace PCM. Program replacement PCM using required equipment. After replacing PCM, 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 this DTC. If scan tool displays that this DTC FAILED THIS IGN, return to step 2 . If scan tool does not display that this DTC FAILED THIS IGN, repair is complete.

DTC P1652: FAN 2 RELAY CONTROL CIRCUIT (3.1L "N" & "W" BODIES)

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

DTC will set when ignition is on, an improper voltage level detected on ODM B output No. 2 (high speed fan relay driver circuit) and conditions are present for at least 30 seconds.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(ref-132811-S27457185922002013000000) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Turn ignition off. Disconnect PCM connector. Turn ignition on. Using DVOM, check voltage between ground and high speed fan control circuit terminal at PCM connector. If battery voltage is present, go to next step. If battery voltage is not present, go to step 7 .
Turn ignition off. Remove cooling fans No. 2 and 3 relays. Check voltage between high speed fans control circuit and ground. If voltage reading is zero volts, go to next step. If voltage reading is not zero volts, go to step 6 .
Replace cooling fans No. 2 and 3 relays. Set DVOM to 10-amp scale. Turn ignition on. Check current between ground and high speed fan control circuit terminal at PCM connector. Monitor reading for a minimum of 2 minutes. If current is 0.1-1.5 amps, go to step 12 . If current is not 0.1-1.5 amps, go to next step.
Turn ignition off. Remove cooling fan 3 relay. Turn ignition on. Set DVOM to 10-amp scale. Turn ignition on. Using DVOM, check current between ground and cooling fan 3 relay control circuit at relay connector. If current reads 0.1-1.5 amps, go to step 15 . If current does not read 0.1-1.5 amps, go to step 16 .
Locate and repair short to voltage in high speed fan control circuit. After repairs, go to step 18 .
Check battery voltage feed fuse for cooling fans No. 2 and 3 relays. If fuse is blown, go to next step. If fuse is okay, go to step 9 .
Locate and repair short to ground in battery positive feed circuit for fan No. 3 relay. Replace fuse. After repairs, go to step 18 .
Disconnect cooling fan No. 3 relay. Turn ignition on. Check voltage between ground and battery feed circuit terminal at cooling fan No. 3 relay connector. If battery voltage is present, go to next step. If battery voltage is not present, go to step 14 .
Check high speed fan control circuit for open or short to ground. Repair as necessary. After repairs, go to step 18 . If circuit is okay, go to next step.
Check output driver circuit and battery feed circuit for poor connection at cooling fan No. 3 relay and PCM. Repair as necessary. After repairs, go to step 18 . If connection is okay, go to step 15 .
Turn ignition off. Reconnect PCM connector. Disconnect cooling fan No. 3 relay connector. Turn ignition on. Using scan tool, select output test function and cycle cooling fan No. 3 relay on and off. If test light flashes on and off, see «DIAGNOSTIC AIDS»(/gmc/savana/i-1996-2002/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p1537-u1193) . If test light does not flash on and off, go to next step.
Check high speed fan control circuit for poor terminal connection at PCM. Repair as necessary. After repairs, go to step 18 . If connection is okay, go to step 17 .
Locate and repair open in battery feed circuit to cooling fan Nos. 2 and 3 relay, or poor terminal connection between cooling fan No. 2 Maxifuse® and fuse block. Repair as necessary. After repairs, go to step 18 .
Replace cooling fan No. 3 relay. After replacing relay, go to step 18 .
Replace cooling fan No. 2 relay. After replacing relay, go to step 18 .
Replace PCM. Program replacement PCM using required equipment. After replacing PCM, go to next step.
Using scan tool, select CLEAR INFO or CLEAR DTCs function to 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 P1652 until DTC P1652 test runs. If scan tool indicates FAILED THIS IGN, repeat step 2 . If scan tool does not indicate FAILED THIS IGN, repair is complete.

DTC P1652: FAN 2 RELAY CONTROL CIRCUIT (3.4L "N" BODY)

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

Output Driver Modules (ODMs) are used by Powertrain Control Module (PCM) to turn on current driven devices that are needed to control various engine and transaxle functions. Each ODM can control up to 7 separate outputs by grounding the device that PCM is commanding on. ODMs can diagnose each output circuit individually. DTC P1652 indicates an improper voltage level has been detected on cooling fan 2 relay driver (control) circuit.

DTC will set when ignition is on, an improper voltage level detected on ODM B output No. 2 (cooling fan relay No. 2 driver circuit) and conditions are present for at least 30 seconds.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(ref-132811-S27457185922002013000000) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Turn ignition off. Disconnect PCM harness connector. Turn ignition on. Using DVOM, check voltage between ground and high speed fan control circuit. If battery voltage is present, go to next step. If battery voltage is not present, go to step 7 .
Turn ignition off. Remove cooling fan No. 2 and 3 relays. Leave PCM harness connector disconnected. Using DVOM, check voltage between high speed fans control circuit and ground. If voltage reading is zero volts, go to next step. If voltage reading is not zero volts, go to step 6 .
Reinstall cooling fan No. 2 and 3 relays. Using DVOM, set DVOM to 10-amp range. Turn ignition on. Check current between ground and high speed fans control circuit. Monitor reading for about 2 minutes. If current is 0.1-1.5 amps, go to step 12 . If current is not 0.1-1.5 amps, go to next step.
Turn ignition off. Remove fan No. 3 relay connector. Turn ignition on. Using DVOM, set DVOM to 10-amp range. Check voltage between ground and fan 3 relay driver circuit. If current reading is 0.1-1.5 amps, go to step 15 . If current reading is not 0.1-1.5 amps, go to step 16 .
Locate and repair short to voltage in high speed fans control circuit. After repairs, go to step 18 .
Check battery feed fuse to cooling fan relay No. 2 and 3. If fuse is blown, go to next step. If fuse is okay, go to step 9 .
Locate and repair short to ground in battery feed circuit for cooling fan No. 3 relay. Replace fuse. After repairs, go to step 18 .
Disconnect cooling fan No. 3 relay. Turn ignition on. Check voltage between ground and battery feed circuit terminal at cooling fan No. 3 relay harness connector. If battery voltage is present, go to next step. If battery voltage is not present, go to step 14 .
Check for an open or short to ground in high speed fan control circuit. Repair as necessary. After repairs, go to step 18 . If circuit is okay, go to step 15 .
Check output driver circuit and battery feed circuit for poor connection at cooling fan No. 3 relay and at PCM. Repair as necessary. After repairs, go to step 18 . If circuits are okay, go to step 15 .
Turn ignition off. Reconnect PCM harness connector. Disconnect cooling fan No. 3 relay. Turn ignition on. Connect a test light between ground and cooling fan No. 3 relay control circuit terminal. Using scan tool, cycle cooling fan No. 3 relay on and off. If test light flashes on and off, see «DIAGNOSTIC AIDS»(/gmc/savana/i-1996-2002/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p1537-u1193) . If test light does not flash on and off, go to next step.
Check high speed fans control circuit for poor connection at PCM. Repair as necessary. After repairs, go to step 18 . If connections are okay, go to step 17 .
Locate and repair open on battery feed circuit to cooling fan No. 2 and 3 relays. Check for poor terminal connections between cooling fan No. 2 Maxi-Fuse® and fuse block. Repair as necessary. After repairs, go to step 18 .
Replace cooling fan No. 3 relay. After replacing relay, go to step 18 .
Replace cooling fan No. 2 relay. After replacing relay, go to step 18 .
Replace PCM. Program replacement PCM using required equipment. After replacing PCM, go to next step.
Using scan tool, select CLEAR INFO or CLEAR DTCs function to 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 this DTC until DTC test runs. If scan tool indicates that this DTC FAILED THIS IGN, repeat step 2 . If scan tool does not indicate that this DTC FAILED THIS IGN, repair is complete.

DTC P1652: FAN 2 RELAY CONTROL CIRCUIT (3.8L "C", "G", "H" & "W" BODIES)

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

Output Driver Modules (ODM) are used by PCM to turn on current-driven devices needed to control various engine and transaxle functions. Each ODM can control up to 7 outputs, including fan 2 relay, by supplying ground to device PCM is commanding on. ODMs can diagnose each circuit individually. If ODM "B" output 2 (fan 2 relay driver circuit) detects an improper voltage level, DTC will set.

Conditions for setting DTC are: ignition is on, an improper voltage level has been detected on fan 2 relay driver circuit and conditions present for at least 30 seconds.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(ref-132811-S27457185922002013000000) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Turn ignition off. Disconnect PCM harness connectors. Turn ignition on. Using a DVOM, check voltage between engine ground and PCM harness connector fan 2 relay driver circuit. If battery voltage is present, go to next step. If battery voltage is not present, go to step 6 .
Disconnect cooling fan connectors. Using DVOM in 10-amp scale, check current between engine ground and fan 2 relay driver circuit for 2 minutes. If current remains.05-.50 amp, go to step 11 . If current does not remain between.05-.50 amp, go to next step.
Ignition off. With PCM harness connectors still disconnected, disconnect series/parallel and high speed fan relays. Turn ignition on. Using DVOM, check voltage between engine ground and fan 2 relay driver circuit. If voltage reading is zero volts, go to step 10 . If voltage reading is not zero volts, go to next step.
Locate and repair short to voltage in fan 2 relay driver circuit. After repairs, go to step 16 .
Check fan 2 relay ignition feed fuse. If fuse is blown, go to next step. If fuse is okay, go to step 8 .
Locate and repair short to ground in fan 2 relay ignition feed circuit. Replace fuse. After repairs, go to step 16 .
Disconnect fan 2 (high speed) relay connector. Turn ignition on. Check voltage between engine ground and fan 2 relay ignition feed circuit. If battery voltage is present, go to next step. If battery voltage is not present, go to step 13 .
Check fan 2 relay driver circuit for open or short to ground. Repair as necessary. After repairs, go to step 16 . If circuit is okay, go to next step.
Check fan 2 relay driver and fan 2 relay ignition feed circuits for faulty connection at PCM. Repair as necessary. After repairs, go to step 16 . If connection is okay, go to step 14 .
Turn ignition off. Reconnect PCM connector. Disconnect high speed cooling fan relay connector. Turn ignition on. Connect a test light between fan 2 relay harness connector fan 2 relay driver and ignition feed circuits. Using scan tool, cycle fan 2 relay on and off. If test light flashes on and off, see «DIAGNOSTIC AIDS»(/gmc/savana/i-1996-2002/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p1537-u1193) . If test light does not flash on and off, go to next step.
Check fan 2 relay driver circuit for faulty connection at PCM. Repair as necessary. After repairs, go to step 16 . If connection is okay, go to step 15 .
Locate and repair open fan 2 relay ignition feed circuit. After repairs, go to step 16 .
Replace high speed cooling fan relay. After replacing relay, go to step 16 .
Replace PCM. Program replacement PCM using required equipment. After replacing PCM, 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 this DTC. If scan tool displays that this DTC FAILED THIS IGN, return to step 2 . If scan tool does not display that this DTC FAILED THIS IGN, repair is complete.

Check for faulty connections or damaged harness. Disconnect PCM connector. Turn ignition on. Connect a DVOM between engine ground and PCM harness connector fan 2 relay driver circuit. Observe DVOM while moving all related harness and connectors. A change in voltage display indicates fault location.

DTC P1652: POWERTRAIN INDUCED CHASSIS PITCH OUTPUT CIRCUIT (4.6L "E" & "K" BODIES)

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

PCM contains chips called Output Driver Modules (ODM) that provide 7 switchable ground outputs for operating solenoids, relays, warming lights, and other devices. Each of these ground outputs has an internal fault line that feeds back to the PCM. When output is off, the output driver should receive 12 volts, fed to the solenoid driver, etc. When output is on, it should receive zero volts, since it is grounding the output. If it receives zero volts when output is off or 12 volts when output is on, it sets the fault line low.

DTC P1652 is used to monitor the fault line of the lift/dive output to the Road Sensing Suspension (RSS) module. The RSS module sends a 12 volt signal to the PCM connector C1 terminal No. 24. The PCM then grounds this circuit when vehicle is accelerating rapidly (lift) or braking hard (dive). The RSS module will then command the suspension to "firm", increasing controllability of vehicle during these conditions. DTC will set when fault line is low for 2 seconds.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(ref-132811-S27457185922002013000000) 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 PCM ride control output signal display. If display indicates OK, go to next step. If display does not indicate OK, go to step 5 .
Start and operate engine at idle. Using scan tool, command ride control to "firm". If display indicates OK, fault is not present. See «DIAGNOSTIC AIDS»(/gmc/savana/i-1996-2002/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p1537-u1193) . If display does not indicate OK, go to next step.
Turn ignition off. Disconnect RSS module harness connector. Turn ignition on. Using DVOM, check voltage between ground and RSS module connector terminal A7. If voltage reading is 0.5 volt or greater, go to step 8 . If voltage reading is not 0.5 volt or greater, go to step 12 .
Store fluid life index. Turn ignition off. Wait 30 seconds, then disconnect PCM harness connector C1. Turn ignition on. Check voltage between ground and PCM harness connector C1 terminal No. 24. If voltage reading is 10 volts or greater, go to step 12 . If voltage reading is not 10 volts or greater, go to next step.
Turn ignition off. Disconnect RSS harness connector. Check resistance between ground and RSS module harness connector terminal A7. If resistance is 10,000 ohms or less, go to step 9 . If resistance is not 10,000 ohms or less, go to next step.
Check resistance between PCM harness connector C1 terminal No. 24 and RSS module harness connector terminal A7. If resistance is 5 ohms or less, go to step 11 . If resistance is not 5 ohms or less, go to step 10 .
Repair short to voltage on circuit No. 1490.
Repair short to ground on circuit No. 1490.
Repair open in circuit No. 1490.
Check terminal contact at RSS module. Repair as necessary. If repair is not required, diagnose RSS system.
Check for faulty terminal contact at PCM harness connector C1 terminal No. 24. Repair as necessary. If repair is not required, go to next step.
Replace PCM. Program replacement PCM using required equipment.

Use Failure Records to aid in diagnosing an intermittent fault. Use the data captured when the was DTC set, to determine is an open or shorted condition caused the DTC to set.

DTC P1652: PCM CHASSIS PITCH OUTPUT CIRCUIT (5.7L "Y" BODY)

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

PCM controls Powertrain Induced Chassis Pitch (PICP) by grounding control circuit through an internal switch called a driver. The 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 on control circuit should be low (near zero). When PCM is commanding a component off, voltage of circuit should be high (near battery voltage). If fault detection circuit senses a voltage other that what is expected, fault line will change causing DTC to set.

PCM receives ignition voltage feed from Electronic Suspension Control (ESC) module from PICP circuit. PCM grounds this circuit when vehicle is accelerating rapidly or braking hard. ESC module commands all four shock absorber solenoids to firm position.

DTC will set when PCM detects that commanded state of driver and actual state do not match and condition met for at least 5 seconds.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(ref-132811-S27457185922002013000000) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Turn ignition off. Disconnect Electronic Suspension Control (ESC) module harness connector. Turn ignition on, with engine off. Using a test light connected to battery voltage, probe powertrain induced chassis pitch control circuit. If test light illuminates, go to step 4 . If test light does not illuminate, go to next step.
Using scan tool, command chassis pitch signal ON. If test light illuminates, repair Electronic Suspension System as necessary. See appropriate ELECTRONIC article in SUSPENSION. If test light does not illuminate, go to step 5 .
Check chassis pitch control circuit for short to ground. Repair as necessary. After repairs, go to step 8 . If circuit is okay, go to step 7 .
Check chassis pitch control circuit for open. Repair as necessary. After repairs, go to step 8 . If circuit is okay, go to next step.
Check terminal connections at PCM. Repair terminals as necessary. After repairs, go to step 8 . If terminals are okay, go to next step.
Replace PCM. Program replacement PCM using required equipment. After replacing PCM, go to next step.
Using scan tool, select DTC, CLEAR INFO function. Start and warm engine to normal operating temperature. Select DTC, SPECIFIC, then enter this DTC. 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, repeat step 2 .
Using scan tool, select CAPTURE INFO, REVIEW INFO function. If any undiagnosed DTCs are displayed, go to applicable DTC test.

DTC P1653: LOW OIL LIGHT CIRCUIT FAULT (3.1L "W" BODY - LUMINA & MONTE CARLO & 3.4L "U" SERIES)

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

The Output Driver Module (ODM) is used by the PCM to turn on many of the current-driven devices that are needed to control various engine and transaxle functions. Each ODM is capable of controlling up to 7 separate outputs by applying ground to the device which the PCM is commanding on.

ODM have the capability of diagnosing each output circuit individually. DTC will set when an improper voltage level has been detected on the output circuit that controls the LOW OIL light.

A history DTC will clear after 40 consecutive warm-up cycles have occurred without a malfunction. DTC will also clear when battery is disconnected or cleared by scan tool.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(ref-132811-S27457185922002013000000) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Turn ignition off. Disconnect PCM harness connector. Turn ignition on, with engine off. Using DVOM, check voltage between ground and low engine oil level light control circuit at PCM harness connector. If battery voltage is present, go to next step. If battery voltage is not present, go to step 6 .
Set DVOM to 10-amp scale. Check and observe current between ground and low engine oil level light control circuit for 2 minutes. If reading is 0.05-0.50 amps, go to step 11 . If reading is not 0.05-0.50 amps, go to next step.
Turn ignition off. Disconnect instrument cluster harness connector. Turn ignition on, with engine off. Check voltage between ground and low engine oil level light control circuit at PCM harness connector. If voltage reading is zero volts, go to step 10 . If voltage reading is not zero volts, go to next step.
Locate and repair short to voltage in low engine oil level light control circuit. After repairs, go to step 15 .
Check ignition feed fuse for instrument panel cluster indicator lights. If fuse is blown, go to next step. If fuse is okay, go to step 8 .
Locate and repair short to ground in ignition feed circuit for instrument panel cluster indicator lights. Replace fuse. After repairs, go to step 15 .
Disconnect instrument panel cluster harness connector. Turn ignition on, with engine off. Check voltage between ignition feed circuit for instrument panel cluster indicator lights and ground. If voltage reading is about battery voltage, go to next step. If voltage reading is not about battery voltage, go to step 13 .
Check low engine oil level light control circuit for open or short to ground. Repair as necessary. After repairs, go to step 15 . If circuit is okay, go to next step.
Check low engine oil level light control circuit and instrument panel indicator ignition feed circuit for poor connection at PCM and instrument cluster. Repair as necessary. After repairs, go to step 15 . If connections are okay, diagnose instrument cluster. See appropriate INSTRUMENT PANELS article in ACCESSORIES & EQUIPMENT.
Turn ignition off. Reconnect PCM harness connector. Leave instrument cluster harness connector disconnected. Turn ignition on, with engine off. Using a test light, connect test light between low engine oil level light control circuit and ignition feed circuit at instrument panel harness connector. Using scan tool in OUTPUTS TESTS function, cycle low engine oil level light circuit on and off. If test light flashes on and off, see «DIAGNOSTIC AIDS»(/gmc/savana/i-1996-2002/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p1537-u1193) . If test light does not flash on and off, go to next step.
Check low engine oil level light control circuit for poor connection at PCM. Repair as necessary. After repairs, go to step 15 . If connections are okay, go to step 14 .
Locate and repair open in ignition feed circuit to instrument panel indicator lights. After repairs, go to step 15 .
Replace PCM. Program replacement PCM using required equipment. After replacing PCM, 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 this DTC. If scan tool displays that this DTC FAILED THIS IGN, return to step 2 . If scan tool does not display that this DTC FAILED THIS IGN, system is okay.

A PCM controlled light that is on at all times most likely indicates that a condition is present, requiring vehicle operator's attention. Check for poor connections at PCM or for damaged harness. If harness appears to be okay, disconnect PCM connector and turn ignition on. Using a DVOM, connect DVOM to affected PCM output circuit while moving connectors and harnesses related to PCM output circuit. A change in voltage will indicate location of fault.

DTC P1654: CRUISE DISABLE OUTPUT CIRCUIT (4.0L "G" BODY & 4.6L "E" & "K" BODIES)

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

PCM contains Output Driver Modules (ODM) that provides 7 switchable ground outputs for operating solenoids, relays, indicator lights, and other devices. Each of these ground outputs has fault lines that feed back to the PCM's microprocessor. When the output is off, the output driver should receive the 12 volts fed to the solenoid, relay, etc. When the output is on, it should receive zero volts, since it is grounding the output. When PCM sees zero volts when the output is off or 12 volts when the output is on, it sets a fault line low.

DTC P1645 is used to monitor the fault line of cruise disable output to the cruise control module. The cruise control module sends ignition voltage on the cruise inhibit output circuit to the PCM. The PCM will then ground this circuit to disengage cruise control module, if engaged or inhibit cruise control operation, if requested. DTC will set when fault line is low for 2 seconds.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(ref-132811-S27457185922002013000000) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Turn ignition on. Using scan tool, select ENGINE 3 mode and note CRUISE ENABLE DRIVER display. If scan tool display indicates OK, go to next step. If scan tool display does not indicate OK, go to step 6 .
Store fluid life index as indicated on scan tool. Turn ignition off and wait 30 seconds, then disconnect PCM harness connector C1. Turn ignition on. Using DVOM, check voltage between ground and cruise inhibit output circuit at PCM harness connector C1. If voltage reading is 10 volts or greater, fault is not present. See «DIAGNOSTIC AIDS»(/gmc/savana/i-1996-2002/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p1537-u1193) . If voltage reading is not 10 volts or greater, go to next step.
Turn ignition off. Disconnect cruise control module harness connector. Check resistance between ground and cruise control module harness connector terminal "H". If resistance is 5 ohms or less, go to step 8 . If resistance is not 5 ohms or less, go to step 9 .
Check resistance of cruise inhibit output circuit between cruise control module harness connector and PCM harness connector terminals. If resistance is 5 ohms or less, go to step 7 . If resistance is not 5 ohms or less, go to step 9 .
Store fluid life index as indicated on scan tool. Turn ignition off and wait 30 seconds, then disconnect PCM harness connector C1. Disconnect cruise control module. Turn ignition on. Using DVOM, check voltage between ground and cruise inhibit output circuit at PCM harness connector C1 terminal. If voltage reading is 10 volts or greater, go to step 10 . If voltage reading is not 10 volts or greater, go to step 14 .
Turn ignition on. Check voltage to ground at cruise control module terminal "F". If voltage reading is 10 volts or greater, go to step 12 . If voltage reading is not 10 volts or greater, go to step 11 .
Repair short to ground in cruise inhibit output circuit.
Repair open in cruise inhibit output circuit.
Repair short to voltage in cruise inhibit output circuit.
Repair open or short to ground (if fuse is blown) in ignition circuit to TCC brake switch and to cruise control module.
Check terminal contact at cruise control module. Repair as necessary. If terminal contact is okay, go to next step.
Replace cruise control module.
Check terminal contact at PCM. Repair as necessary. If terminal contact is okay, go to next step.
Replace PCM. Program replacement PCM using required equipment. After replacing PCM, go to next step.

Use the FAILURE REC. to aid in diagnosing an intermittent fault. Use the data captured when the DTC set to determine if an open or shorted condition caused the DTC to set.

A generic Field Effects Transistor (FET) driver is used to operate all the actuators. This DTC will set if the PCM/TCM has determined this device has failed.

Record and diagnose DTC(s) present. Clear DTC(s). If DTC P1660 resets, replace PCM. Program replacement PCM using required equipment.

DTC P1660: COOLING FAN CONTROL CIRCUITS (4.0L "G" BODY)

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

PCM contains Quad Driver Modules (QDM) that provides 4 switchable ground outputs for operating solenoids, relays, indicator lights, and other devices. Each of these ground outputs has fault lines that feed back to the PCM's microprocessor. When the output is off, the output driver should receive the 12 volts fed to the solenoid, relay, etc. When the output is on, it should receive zero volts, since it is grounding the output. When PCM sees zero volts when the output is off or 12 volts when the output is on, it sets a fault line low.

DTC P1645 is used to monitor the fault line of the cooling fan control relay output and the starter inhibit output.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(ref-132811-S27457185922002013000000) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Turn ignition on. Turn off A/C. Using scan tool in MISC TESTS, select OUTPUT TESTS then select FAN RELAYS. Command all relays off and note QUAD DRIVER 1. If scan tool display indicates okay, go to next step. If scan tool display does not indicate OK, go to step 9 .
Command all relays off and note QUAD DRIVER 1 display on scan tool. If scan tool display indicates OK, go to next step. If scan tool display does not indicate OK, go to step 6 .
Turn ignition on, with engine off. Command STARTER INHIBIT on. If QUAD DRIVER 1 on scan tool display indicates OK, go to next step. If scan tool display does not indicate OK, go to step 20 .
If cooling operation fault is suspected, diagnose cooling fan. See appropriate SYSTEM & COMPONENT TESTING article. If cooling fan is operating properly, fault it not present.
While noting QUAD DRIVER 1 display, command FAN RELAY 1 on. If scan tool display indicates OK, go to step 8 . If scan tool display does not indicate OK, go to next step.
Store fluid life index as indicated on scan tool. Turn ignition off and wait 30 seconds, then disconnect PCM harness connector C2. Remove cooling fan relay No. 1 (low speed). Turn ignition on. Using DVOM, check voltage between ground and cooling fan low speed control circuit at PCM harness connector C2 terminal. If voltage reading is.5 volt or less, go to step 27 . If voltage reading is not.5 volt or less, go to step 18 .
Store fluid life index as indicated on scan tool. Turn ignition off. Wait 30 seconds, then disconnect PCM harness connector C2. Remove cooling fan relays No. 2 and 3. Turn ignition on, engine off. Using DVOM, check voltage between ground and cooling fan high speed control circuit at PCM harness connector C2. If voltage reading is.5 volt or less, go to step 27 . If voltage reading is not.5 volt or less, go to step 19 .
In ENGINE 3 data list mode, note PASSKEY STARTER display on scan tool. If scan tool display indicates ENABLED, go to next step. If scan tool display does not indicate ENABLED, go to step 21 .
With all relays still commanded off, observe operation of both cooling fans. If either fan operates, go to next step. If either fan does not operate, go to step 12 .
Store fluid life index as indicated on scan tool. Turn ignition off and wait 30 seconds, then disconnect PCM harness connector C2. Turn ignition on. Using DVOM, check voltage between ground and cooling fan low speed control circuit at PCM harness connector C2. If voltage reading is 10 volts or greater, go to step 16 . If voltage reading is not 10 volts or greater, go to step 17 .
Store fluid life index as indicated on scan tool. Turn ignition off and wait 30 seconds, then disconnect PCM harness connector C2. Turn ignition on. Using DVOM, check voltage between ground and cooling fan high and low speed control circuits at PCM harness connector C2. If voltage reading on both terminals is 10 volts or greater, go to step 27 . If voltage reading on both terminals is not 10 volts or greater, go to next step.
If voltage measured is low on both terminals, go to step 15 . If voltage measured is low only on one of the terminals, go to next step.
Repair open circuit or replace open cooling fan relay for circuit that measured low in step 9 .
Repair cause of no voltage to both circuits. Replace fuse, if faulty. A no voltage to both circuits can be caused by, open in both the high and low cooling fan control circuits, open in ignition circuit to both relays, short to ground in ignition circuit to both relays (fuse blown), short fan relay(s), short to ground in ignition circuit to A/C compressor relay (fuse blown) or shorted A/C compressor relay (blown fuse).
Repair short to ground in cooling fan high speed control circuit.
Repair short to ground in cooling fan low speed control circuit.
Repair short to voltage in cooling fan low speed control circuit.
Repair short to voltage in cooling fan high speed control circuit.
Store fluid life index as indicated on scan tool. Turn ignition off and wait 30 seconds, then disconnect PCM harness connector C2 and PASS-Key® module harness connector. Turn ignition on. Using DVOM, check voltage between ground and starter inhibit output circuit at PCM harness connector C2. If voltage reading is greater than.5 volt, go to step 24 . If voltage reading is not greater than.5 volt, go to step 27 .
Store fluid life index as indicated on scan tool. Turn ignition off and wait 30 seconds, then disconnect PCM harness connector C2. Turn ignition on. Using DVOM, check voltage between ground and starter inhibit output circuit at PCM harness connector C2. If voltage reading is 10 volts or greater, go to step 27 . If voltage reading is not 10 volts or greater, go to next step.
Turn ignition off. Disconnect PASS-Key® module harness connector. Check resistance between ground and starter inhibit output circuit at PCM harness connector C2. If resistance is 10,000 ohms or greater, go to next step. If resistance is not 10,000 ohms or greater, go to step 25 .
Check resistance on starter inhibit output circuit between PCM harness connector C2 and PASS-Key® harness connector terminals. If resistance is less than 5 ohms, fault is not present. Diagnose anti-theft deterrent system. See appropriate ANTI-THEFT SYSTEMS article in ACCESSORIES & EQUIPMENT. If resistance is not less than 5 ohms, go to step 26 .
Repair short to voltage in starter inhibit output circuit.
Repair short to ground in starter inhibit output circuit.
Repair open in starter inhibit output circuit.
Check terminal contact at PCM. Repair as necessary. If terminal contact is okay, go to next step.
Replace PCM. Program replacement PCM using required equipment.

DTC P1660: COOLING FAN CONTROL CIRCUITS (4.6L "E" & "K" BODIES - EXCEPT SEVILLE)

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

PCM Quad Driver Module (QDM) provides 4 switchable ground outputs for operating solenoids, relays, warning lights, and other devices. Each of these ground outputs has an internal fault line that feed back to the PCM. When the output is off, the quad driver should receive 12 volts fed to the solenoids, relays, etc. When the output is on, it should receive zero volts, since it is grounding the output. If it receives zero volts when the output is off or 12 volts when the output is on, it sets the fault line low. DTC is used to monitor the fault line of the cooling fan control relay output. DTC will set when fault line is low for 2 seconds.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(ref-132811-S27457185922002013000000) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Turn ignition on. Turn A/C controls off. Using scan tool in MISC TESTS select OUTPUT TESTS, then select FAN RELAYS. Note QUAD DRIVER 1 display and command ALL RELAYS off. If scan tool display indicates OK, go to next step. If scan tool display does not indicate OK, go to step 8 .
In MISC TESTS, select OUTPUT TESTS, then select FAN RELAYS. Note QUAD DRIVER 1 display and ALL RELAYS on. If scan tool display indicates OK, go to next step. If scan tool display does not indicate OK, go to step 5 .
If cooling fan is inoperative or if a fault is suspected, diagnose cooling fan. See appropriate SYSTEM & COMPONENT TESTING article. If cooling fan operates, fault is not present.
While noting QUAD DRIVER 1 display, command FAN RELAY 1 on. If scan tool display indicates OK, go to step 7 . If scan tool display does not indicate OK, go to next step.
Store fluid life index as indicated on scan tool. Turn ignition to LOCK position and wait 30 seconds, then disconnect PCM harness connector C2. Remove fan relay 1 (low speed). Using DVOM, check voltage between ground and cooling fan low speed control circuit at PCM harness connector terminal. If voltage reading is.5 volt or less, go to step 18 . If voltage reading is not.5 volt or less, go to step 16 .
Store fluid life index as indicated on scan tool. Turn ignition switch to LOCK position and wait 30 seconds, then disconnect PCM harness connector C2. Remove fan relays 2 and 3. Using DVOM, check voltage between ground and cooling fan high speed control circuits at PCM harness connector. If voltage reading is.5 volt or less, go to step 18 . If voltage reading is not.5 volt or less, go to step 17 .
With ALL RELAYS still commanded off, observe operation of both cooling fans. If either fan is operating, go to next step. If neither fan is operating, go to step 10 .
Store fluid life index as indicated on scan tool. Turn ignition switch to LOCK position. Wait 30 seconds, then disconnect PCM harness connector C2. Turn ignition on. Using DVOM, check voltage between ground and cooling fan low speed control circuits at PCM harness connector. If voltage reading is less than 10 volts, go to step 15 . If voltage reading is not less than 10 volts, go to step 14 .
Store fluid life index as indicated on scan tool. Turn ignition to LOCK position and wait 30 seconds, then disconnect PCM harness connector C2. Turn ignition on. Using DVOM, check voltage between ground and cooling fan high and low speed control circuits at PCM harness connector. If voltage reading is 10 volts or greater, go to step 18 . If voltage reading is not 10 volts or greater, go to next step.
If voltage reading from step 9 is low for both terminals, go to step 13 . If voltage reading from step 9 is low only in one of the terminals, go to next step.
Repair open in circuit or replace fan relay for the circuit that measured low.
Repair cause of no voltage to both circuits. Replace fuse if blown.
Repair short to ground in cooling fan high speed control circuit.
Repair short to ground in cooling fan low speed control circuit.
Repair short to voltage in cooling fan low speed control circuit.
Repair short to voltage in cooling fan high speed control circuit.
Check terminal contact at PCM. Repair as necessary. If terminal contact is okay, go to next step.
Replace PCM. Program replacement PCM using required equipment.

DTC P1660: COOLING FAN CONTROL CIRCUITS (4.6L "K" BODY - SEVILLE)

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»(ref-132811-S27457185922002013000000) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Turn ignition on. Turn A/C controls off. Using scan tool in MISC TESTS select OUTPUT TESTS, then select FAN RELAYS. Note QUAD DRIVER 1 display and command ALL RELAYS off. If scan tool display indicates OK, go to next step. If scan tool display does not indicate OK, go to step 6 .
Command the low speed relay ON. If scan tool display indicates OK, go to next step. If scan tool display does not indicate OK, go to step 8 .
Command all relays OFF. If scan tool display indicates OK, go to next step. If scan tool display does not indicate OK, go to step 9 .
If cooling fan is inoperative or if a fault is suspected, diagnose cooling fan. See appropriate SYSTEM & COMPONENT TESTING article. If cooling fan operates, fault is not present.
Store fluid life index as indicated on scan tool. Turn ignition switch to LOCK position. Wait 30 seconds, then disconnect PCM harness connector C2. Turn ignition on. Using DVOM, check voltage between ground and cooling fan low speed relay control circuit at PCM harness connector terminal No. 32. If voltage reading is 10.5-15 volts or greater, go to next step. If voltage reading is not 10.5-15 volts or greater, go to step 11 .
Check voltage between ground and high speed fan relay control circuit at PCM harness connector terminal No. 33. If voltage reading is 10.5-15 volts or greater, go to step 14 . If voltage reading is not 10.5-15 volts or greater, go to step 10 .
Store fluid life index as indicated on scan tool. Turn ignition switch to LOCK position. Wait 30 seconds, then disconnect PCM harness connector C2. Remove cooling fan relay No. 2 (low speed). Turn ignition on. Using DVOM, check voltage between ground and cooling fan low speed control circuits at PCM harness connector terminal No. 32. If voltage reading is.5 volt or less, go to step 14 . If voltage reading is not.5 volt or less, go to step 12 .
Store fluid life index as indicated on scan tool. Turn ignition switch to LOCK position. Wait 30 seconds, then disconnect PCM harness connector C2. Remove low and high speed cooling fan relays. Turn ignition on. Using DVOM, check voltage between ground and cooling fan high speed control circuits at PCM harness connector terminal No. 33. If voltage reading is.5 volt or less, go to step 14 . If voltage reading is not.5 volt or less, go to step 13 .
Repair open, short to ground, open relay, or blown fuse in high speed fan control circuit between PCM and underhood fuse/relay block.
Repair open, short to ground, open relay, or blown fuse in low speed fan control circuit between PCM and underhood fuse/relay block.
Repair short to voltage in low speed fan control circuit between PCM and underhood fuse/relay block.
Repair short to voltage in high speed fan control circuit between PCM and underhood fuse/relay block.
Check terminal contact in PCM. Repair as necessary. After repairs, go to next step.
Replace PCM. Program replacement PCM using required equipment.

DTC P1662: CRUISE CONTROL LIGHT CONTROL CIRCUIT (3.0L "V" BODY)

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

DTC will run if battery voltage is 7.5-15.0 volts, vehicle speed is greater than 40 MPH and cruise control is engaged. DTC will set when ECM internal fault is present for longer than 500 milliseconds.

DTC will clear after 40 consecutive warm-up cycles in which no failures are reported by this diagnostic or any other non-essential related diagnostic, battery is disconnected or cleared by scan tool.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(ref-132811-S27457185922002013000000) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Turn cruise control off. Turn ignition on. Using scan tool, read cruise control status. If scan tool displays cruise control as off, go to next step. If scan tool does not display cruise control as off, diagnose cruise control system. See appropriate CRUISE CONTROL SYSTEMS article in ACCESSORIES & EQUIPMENT.
Check cruise control indicator light. If indicator light is on with ignition on and cruise control off/disabled, go to next step. If indicator light is not on with ignition on and cruise control off/disabled, go to step 5 .
Turn ignition off. Disconnect ECM harness connector. Check cruise control indicator light. If cruise control indicator light turns off, go to step 6 . If cruise control indicator light does not turn off, go to step 7 .
Check for open in cruise control indicator light circuit from ECM to instrument cluster. Repair as necessary. After repairs, go to step 8 . If circuit is okay, go to next step.
Replace ECM. Program replacement ECM using required equipment and program new ECM with frequency code of the theft deterrent module that is currently on vehicle. After replacing ECM, go to next step.
Repair short to ground in cruise control indicator light circuit. After repairs, go to next step.
Using scan tool, select DTC, CLEAR INFO. Start and warm engine to normal operating temperature. Select DTC, SPECIFIC, 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. If any undiagnosed DTC(s) are displayed, go to applicable DTC test.

DTC P1662: CRUISE CONTROL INHIBIT CIRCUIT (3.1L "N" & "W" BODIES & 3.4L "N" BODY)

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

Output Driver Modules (ODMs) are used by Powertrain Control Module (PCM) to turn on current-driven devices that are needed to control various engine and transaxle functions. Each ODM can control up to 7 separate outputs by grounding the device that PCM is commanding on. ODMs can diagnose each output circuit individually. DTC P1662 indicates an improper voltage level has been detected on cruise inhibit driver (control) circuit.

Conditions for setting this DTC are, ignition on, improper voltage level detected on the cruise inhibit output driver circuit and conditions are present for at least 20 seconds.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(ref-132811-S27457185922002013000000) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Turn ignition off. Disconnect PCM harness connector. Turn ignition on. Using DVOM, check voltage between ground and cruise inhibit driver circuit terminal at PCM connector. If battery voltage is present, go to next step. If battery voltage is not present, go to step 6 .
Set ammeter to 10-amp range. Check current between ground and cruise inhibit driver circuit terminal at PCM connector. Monitor reading for a minimum of 2 minutes. If current is.5 amp, go to step 11 . If current is not.5 amp, go to next step.
Disconnect Stepper Motor Cruise Control (SMCC) module connector. Using DVOM, check voltage between ground and cruise inhibit driver circuit at cruise inhibit harness connector. If voltage reading is zero volts, go to step 14 . If voltage reading is not zero volts, go to next step.
Locate and repair short to voltage in cruise inhibit driver circuit. After repairs, go to step 16 .
Remove and inspect fuse for SMCC module. If fuse is blown, go to next step. If fuse is okay, go to step 8 .
Locate and repair short to ground in ignition feed circuit for SMCC module. Replace fuse. After repair is completed, go to step 16 .
Disconnect SMCC module. Turn ignition on. Check voltage between ground and ignition feed circuit terminal at SMCC module harness connector. If battery voltage is present, go to next step. If battery voltage is not present, go to step 13 .
Check for an open or short to ground in cruise inhibit driver circuit. Repair as necessary. After repairs, go to step 16 . If circuit is okay, go to next step.
Check cruise inhibit driver circuit and ignition feed circuit for poor terminal connection at SMCC module connector and at PCM harness connector. Repair as necessary. After repairs, go to step 16 . If connections are okay, go to step 14 .
Turn ignition off. Reconnect PCM harness connector. Disconnect SMCC module connector. Turn ignition on. Connect a test light between cruise inhibit driver circuit and ignition feed circuit terminals at SMCC module harness connector. Using scan tool, select OUTPUTS TEST function and cycle cruise inhibit on and off. If test light flashes, see «DIAGNOSTIC AIDS»(/gmc/savana/i-1996-2002/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p1537-u1193) . If test light does not flash, go to next step.
Check cruise inhibit driver circuit for poor terminal connection at PCM. Repair as necessary. After repairs, go to step 16 . If connection is okay, go to step 15 .
Locate and repair open in ignition feed circuit to SMCC module. After repairs, go to step 16 .
Replace SMCC module. After replacing module, go to step 16 .
Replace PCM. Program replacement PCM using required equipment. After replacing PCM, go to next step.
Using scan tool, select CLEAR INFO or CLEAR DTCs function to 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 this DTC until DTC test runs. If scan tool indicates that this DTC FAILED THIS IGN, repeat step 2 . If scan tool does not indicate that this DTC FAILED THIS IGN, repair is complete.

DTC P1662: CRUISE CONTROL INHIBIT CIRCUIT (3.8L "C", "G", "H" & "W" BODIES)

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

Quad Driver Modules (QDM) are used by PCM to turn on current-driven devices needed to control various engine and transaxle functions. Each ODM can control up to 7 outputs, including cruise inhibit driver circuit, by supplying ground to device PCM is commanding on. ODMs can diagnose each circuit individually. If ODM detects an improper voltage level in output circuit controlling the stepper motor cruise control inhibit circuit, DTC will set.

Conditions for setting DTC are: ignition is on, an improper voltage level has been detected on output circuit controlling cruise control inhibit circuit and conditions are present for at least 30 seconds.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(ref-132811-S27457185922002013000000) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Turn ignition off. Disconnect PCM harness connector. Turn ignition on. Using a DVOM, check voltage between engine ground and PCM harness connector cruise inhibit driver circuit. If battery voltage is present, go to next step. If battery voltage is not present, go to step 6 .
Using DVOM in 10-amp scale, check current between engine ground and cruise inhibit driver circuit for 2 minutes. If current remains between.001-.500 amp, go to step 11 . If current does not remain between.001-.500 amp, go to next step.
Turn ignition off. With PCM connectors disconnected, disconnect cruise inhibit connector. Turn ignition on. Using DVOM, check voltage between engine ground and Servo Motor Cruise Control (SMCC) module cruise inhibit driver circuit. If voltage reading is zero volts, go to step 10 . If voltage reading is not zero volts, go to next step.
Locate and repair short to voltage in cruise inhibit driver circuit. After repairs, go to step 16 .
Check SMCC module ignition feed fuse. If fuse is blown, go to next step. If fuse is okay, go to step 8 .
Locate and repair short to ground in SMCC module ignition feed circuit. Replace fuse. After repairs, go to step 16 .
Disconnect SMCC module connector. Turn ignition on. Check voltage between engine ground and SMCC module ignition feed circuit. If battery voltage is present, go to next step. If battery voltage is not present, go to step 13 .
Check cruise inhibit driver circuit for open or short to ground. Repair as necessary. After repairs, go to step 16 . If circuit is okay, go to next step.
Check cruise inhibit driver and ignition feed circuits for faulty connection at SMCC module and PCM. Repair as necessary. After repairs, go to step 16 . If connection is okay, go to step 14 .
Turn ignition off. Reconnect PCM connector. Disconnect SMCC module connector. Turn ignition on. Connect a test light between SMCC module harness connector cruise inhibit driver and ignition feed circuits. Using scan tool, cycle cruise inhibit output on and off. If test light flashes on and off, see «DIAGNOSTIC AIDS»(/gmc/savana/i-1996-2002/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p1537-u1193) . If test light does not flash on and off, go to next step.
Check cruise inhibit driver circuit for faulty connection at PCM. Repair as necessary. After repairs, go to step 16 . If connection is okay, go to step 15 .
Locate and repair open SMCC module ignition feed circuit. After repairs, go to step 16 .
Replace SMCC module. After replacing module, go to step 16 .
Replace PCM. Program replacement PCM using required equipment. After replacing PCM, 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 this DTC. If scan tool displays that this DTC FAILED THIS IGN, return to step 2 . If scan tool does not display that this DTC FAILED THIS IGN, repair is complete.

Check for faulty connections or damaged harness. Disconnect PCM connector. Turn ignition on. Connect a DVOM between engine ground and PCM harness connector cruise inhibit driver circuit. Observe DVOM while moving all related harness and connectors. A change in voltage display indicates fault location.

DTC P1663: CHANGE OIL LIGHT CONTROL CIRCUIT (3.1L "W" BODY - LUMINA & MONTE CARLO)

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

Output Driver Modules (ODMs) are used by Powertrain Control Module (PCM) to turn on current-driven devices that are needed to control various engine and transaxle functions. Each ODM can control up to 7 separate outputs by grounding the device that PCM is commanding on. ODMs can diagnose each output circuit individually. This DTC indicates an improper voltage level has been detected on affected driver (control) circuit.

Conditions for setting this DTC are, ignition on, improper voltage level detected on output circuit controlling the CHANGE OIL SOON light and conditions are present for at least 30 seconds.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(ref-132811-S27457185922002013000000) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Check instrument cluster system. See appropriate INSTRUMENT PANELS article in ACCESSORIES & EQUIPMENT. After diagnosing instrument cluster, go to next step.
Turn ignition off. Disconnect PCM harness connector. Using DVOM, check voltage between affected PCM output circuit at PCM harness connector and ground. If voltage reading is about battery voltage, go to next step. If voltage reading is not about battery voltage, go to step 7 .
Set DVOM to 10-amp scale. Check current between affected PCM output circuit and ground. Monitor reading for at least 2 minutes. If current reads between 0.05-0.50 amps, go to step 12 . If current does not read between 0.05-0.50 amps, go to next step.
Disconnect instrument panel cluster connector. Using DVOM, check voltage between affected PCM output circuit and ground. If voltage reading is zero volts, go to step 15 . If voltage reading is not zero volts, go to next step.
Locate and repair short to voltage in affected PCM output circuit. After repairs, go to step 3 .
Remove and inspect fuse for generator light control circuit. If fuse is blown, go to next step. If fuse is okay, go to step 9 .
Locate and repair short to ground in ignition feed circuit for instrument cluster indicator lights. Replace fuse. After repairs, go to step 3 .
Disconnect instrument cluster connector. Turn ignition on. Check voltage between ground and ignition feed circuit terminal at instrument panel cluster connector. If battery voltage is present, go to next step. If battery voltage is not present, go to step 14 .
Check for an open or short to ground in affected light control circuit. Repair as necessary. After repairs, go to step 17 . If circuit is okay, go to next step.
Check affected light control circuit and ignition feed circuit for poor terminal connection at instrument panel cluster connector and at PCM connector. Repair as necessary. After repairs, go to step 17 . If connections are okay, go to step 15 .
Turn ignition off. Reconnect PCM connector. Disconnect instrument panel cluster connector. Turn ignition on. Connect a test light between generator light control circuit and ignition feed circuit terminals at instrument cluster connector. Using scan tool, select OUTPUTS TEST function and cycle generator light on and off. If test light flashes, see «DIAGNOSTIC AIDS»(/gmc/savana/i-1996-2002/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p1537-u1193) . If test light does not flash, go to next step.
Check affected light control circuit for poor terminal connection at PCM. Repair as necessary. After repairs, go to step 17 . If connection is okay, go to step 16 .
Locate and repair open in ignition feed circuit to instrument cluster indicator lights. After repairs, go to step 17 .
Replace instrument cluster. After replacing instrument cluster, go to step 17 .
Replace PCM. Program replacement PCM using required equipment. After replacing PCM, go to next step.
Using scan tool in OUTPUT TESTS function, operate affected light control circuit. If affected light operates properly, system is okay. If affected light does not operate, go to step 3 .

DTC P1663: GENERATOR LIGHT CONTROL CIRCUIT (3.8L "G" BODY)

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

PCM turns on bulb, LED or driver information center indicator by supplying ground through the PCM. DTC will set when ignition is on, an improper voltage level has been detected on generator light driver circuit and conditions are present for at least 30 seconds.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(ref-132811-S27457185922002013000000) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Turn ignition off. Disconnect PCM harness connector. Using DVOM, check voltage between affected PCM output circuit at PCM harness connector and ground. If voltage reading is about battery voltage, go to next step. If voltage reading is not about battery voltage, go to step 7 .
Set DVOM to 10-amp scale. Check current between affected PCM output circuit and ground. Monitor reading for at least 2 minutes. If current reads 002-.500 amp, go to step 11 . If current reading is not.002-.500 amp, go to next step.
Turn ignition off. Disconnect instrument panel cluster connector. Using DVOM, check voltage between affected PCM output circuit and ground. If voltage reading is zero volts, go to step 10 . If voltage reading is not zero volts, go to next step.
Locate and repair short to voltage in generator light control circuit. Repair as necessary. After repairs, go to step 15 .
Check ignition feed circuit for instrument cluster indicator lights. If fuse is open, replace fuse. After repairs, go to next step. If fuse is okay, go to step 8 .
Locate and repair short to ground in ignition feed circuit for instrument cluster indicators. Replace fuse. After repairs, go to step 15 .
Disconnect instrument cluster connector. Turn ignition on. Check voltage between ground and ignition feed circuit terminal at instrument panel cluster connector. If battery voltage is present, go to next step. If battery voltage is not present, go to step 13 .
Check for an open or short to ground in generator light control circuit. Repair as necessary. After repairs, go to step 15 . If circuit is okay, go to next step.
Check generator light control circuit and ignition feed circuit for poor terminal connection at instrument panel cluster connector and at PCM connector. Repair as necessary. After repairs, go to step 15 . If connections are okay, diagnose instrument panel assembly.
Turn ignition off. Reconnect PCM harness connector. Disconnect instrument panel cluster connector. Turn ignition on. Connect a test light between generator light control circuit and ignition feed circuit terminals at instrument cluster connector. Using scan tool, select OUTPUTS TEST function and cycle generator light on and off. If test light flashes, see «DIAGNOSTIC AIDS»(/gmc/savana/i-1996-2002/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p1537-u1193) . If test light does not flash, go to next step.
Check generator light control circuit for poor terminal connection at PCM. Repair as necessary. After repairs, go to step 15 . If connection is okay, go to step 14 .
Locate and repair open in ignition feed circuit to instrument cluster indicator lights. After repairs, go to step 15 .
Replace PCM. Program replacement PCM using required equipment. After replacing PCM, go to next step.
Using scan tool, select CLEAR INFO or CLEAR DTCs function to 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 this DTC until this DTC test runs. If scan tool indicates FAILED THIS IGN, repeat step 2 . If scan tool does not indicate FAILED THIS IGN, repair is complete.

DTC P1665: EVAP VENT SOLENOID CONTROL CIRCUIT (3.1L "N" & "W" BODIES & 3.4L "N" BODY)

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

Conditions required to set DTC are, ignition is on, improper voltage level detected on output circuit controlling EVAP canister vent valve and conditions are present for at least 30 seconds.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(ref-132811-S27457185922002013000000) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Turn ignition off. Disconnect PCM harness connector. Turn ignition on. Using DVOM, check voltage between ground and EVAP canister vent valve control circuit at PCM connector. If battery voltage is present, go to next step. If battery voltage is not present, go to step 6 .
Set ammeter to 10-amp range. Check current between ground and EVAP canister vent valve control circuit at PCM connector. Monitor reading for a minimum of 2 minutes. If current is.1-.8 amp, go to step 11 . If current is not.1-.8 amp, go to next step.
Disconnect EVAP canister vent valve connector. Using DVOM, check voltage between ground and EVAP vent valve solenoid control circuit at harness connector. If voltage reading is zero volts, go to step 14 . If voltage reading is not zero volts, go to next step.
Locate and repair short to voltage in EVAP canister vent valve control circuit. After repairs, go to step 16 .
Turn ignition off. Remove and inspect fuse for EVAP canister vent valve. If fuse is blown, go to next step. If fuse is okay, go to step 8 .
Locate and repair short to ground in ignition feed circuit for EVAP canister vent valve. Replace fuse. After repairs, go to step 16 .
Disconnect EVAP canister vent valve. Turn ignition on. Check voltage between ground and ignition feed circuit for EVAP canister vent valve harness connector. If battery voltage is present, go to next step. If battery voltage is not present, go to step 13 .
Check for an open or short to ground in EVAP canister vent valve control circuit. Repair as necessary. After repairs, go to step 16 . If circuit is okay, go to next step.
Check EVAP canister control circuit and ignition feed circuit for poor terminal connection at EVAP canister vent and at PCM harness connector. Repair as necessary. After repairs, go to step 16 . If connections are okay, go to step 14 .
Turn ignition off. Reconnect PCM harness connector. Disconnect EVAP canister vent valve connector. Turn ignition on. Connect a test light between EVAP canister vent valve control circuit and ignition feed circuit terminals at EVAP canister vent valve connector. Using scan tool, select OUTPUTS TEST function and cycle EVAP vent solenoid on and off. If test light flashes on and off, see «DIAGNOSTIC AIDS»(/gmc/savana/i-1996-2002/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p1537-u1193) . If test light does not flash, go to next step.
Check EVAP canister vent valve control circuit for poor terminal connection at PCM. Repair as necessary. After repairs, go to step 16 . If connection is okay, go to step 15 .
Locate and repair open in ignition feed circuit to EVAP canister vent valve. After repairs, go to step 16 .
Replace EVAP canister vent valve. After replacing vent valve, go to step 16 .
Replace PCM. Program replacement PCM using required equipment. After replacing PCM, go to next step.
Using scan tool, select CLEAR INFO or CLEAR DTCs function to 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 this DTC until this DTC test runs. If scan tool indicates FAILED THIS IGN, repeat step 2 . If scan tool does not indicate FAILED THIS IGN, repair is complete.

Disconnect and inspect PCM and EVAP canister vent valve harness connectors. Inspect for damaged pins, corrosion and loose wires. 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 set.

DTC P1665: EVAP VENT SOLENOID CONTROL CIRCUIT (3.8L "C", "G", "H" & "W" BODIES)

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

DTC will set when ignition is on, an improper voltage level detected on output circuit controlling EVAP canister vent valve and conditions are present for at least 30 seconds.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(ref-132811-S27457185922002013000000) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Turn ignition off. Disconnect PCM connector. Turn ignition on. Using DVOM, check voltage between ground and EVAP canister vent valve control circuit at PCM connector. If battery voltage is present, go to next step. If battery voltage is not present, go to step 6 .
Set ammeter to 10-amp range. Check current between ground and EVAP canister vent valve control circuit at PCM connector. Monitor reading for a minimum of 2 minutes. If current is.1-.8 amp, go to step 11 . If current is not.1-.8 amp, go to next step.
Disconnect EVAP canister vent valve connector. Using DVOM, check voltage between ground and EVAP vent valve solenoid control circuit at harness connector. If voltage reading is zero volts, go to step 14 . If voltage reading is not zero volts, go to next step.
Locate and repair short to voltage in EVAP canister vent valve control circuit. After repairs, go to step 16 .
Turn ignition off. Remove and inspect fuse for EVAP canister vent valve. If fuse is blown, go to next step. If fuse is okay, go to step 8 .
Locate and repair short to ground in ignition feed circuit for EVAP canister vent valve. Replace fuse. After repairs, go to step 16 .
Disconnect EVAP canister vent valve. Turn ignition on. Check voltage between ground and ignition feed circuit for EVAP canister vent valve harness connector. If battery voltage is present, go to next step. If battery voltage is not present, go to step 13 .
Check for an open or short to ground in EVAP canister vent valve control circuit. Repair as necessary. After repairs, go to step 16 . If circuit is okay, go to next step.
Check EVAP canister control circuit and ignition feed circuit for poor terminal connection at EVAP canister vent and at PCM connector. Repair as necessary. After repairs, go to step 16 . If connections are okay, go to step 14 .
Turn ignition off. Reconnect PCM harness connector. Disconnect EVAP canister vent valve connector. Turn ignition on. Connect a test light between EVAP canister vent valve control circuit and ignition feed circuit terminals at EVAP canister vent valve connector. Using scan tool, select OUTPUTS TEST function and cycle EVAP vent solenoid on and off. If test light flashes on and off, see «DIAGNOSTIC AIDS»(/gmc/savana/i-1996-2002/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p1537-u1193) . If test light does not flash, go to next step.
Check EVAP canister vent valve control circuit for poor terminal connection at PCM. Repair as necessary. After repairs, go to step 16 . If connection is okay, go to step 15 .
Locate and repair open in ignition feed circuit to EVAP canister vent valve. After repairs, go to step 16 .
Replace EVAP canister vent valve. After replacing vent valve, go to step 16 .
Replace PCM. Program replacement PCM using required equipment. After replacing PCM, go to next step.
Using scan tool, select CLEAR INFO or CLEAR DTCs function to 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 this DTC until this DTC test runs. If scan tool indicates FAILED THIS IGN, repeat step 2 . If scan tool does not indicate FAILED THIS IGN, repair is complete.

DTC P1667: FUEL PUMP PWM CONTROL CIRCUIT (3.8L "C", "G", "H" & "W" BODIES)

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

Conditions for setting DTC are: ignition is on, improper voltage level detected on fuel pump speed control Pulse Width Modulated (PWM) circuit and conditions present for at least 30 seconds.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(ref-132811-S27457185922002013000000) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Turn ignition off. Disconnect PCM harness connector and fuel pump relay. Using a fused jumper wire, jumper between fuel pump relay connector terminals No. 30 and 87. Turn ignition on. Using DVOM, check voltage between ground and fuel pump speed control PWM circuit at PCM harness connector. If battery voltage is present, go to next step. If battery voltage is not present, go to step 6 .
Check current between ground and fuel pump speed control PWM circuit at PCM connector. Monitor reading for at least 2 minutes. If current remains between.001-.500 amp, go to step 11 . If current reading does not remain between.001-.500 amp, go to next step.
Turn ignition off. Disconnect fuel pump control module connector. Leave PCM connector disconnected. Turn ignition on. Check voltage between fuel pump speed control PWM circuit and ground. If voltage reading is zero volts, go to step 10 . If voltage reading is not zero volts, go to next step.
Locate and repair short to voltage in fuel pump speed control PWM circuit. After repairs, go to step 18 .
Check ignition feed fuse fro fuel pump relay. If fuse is blown, go to next step. If fuse is okay, go to step 8 .
Locate and repair short to ground in ignition feed circuit for fuel pump relay. Replace fuse. After repairs, go to step 18 .
Disconnect fuel pump control module. Turn ignition on. Check voltage between ground and ignition feed circuit for fuel pump control module. If voltage reading is about battery voltage, go to next step. If voltage reading is not about battery voltage, go to step 13 .
Check fuel pump speed control PWM circuit for open or short to ground. Repair as necessary. After repairs, go to step 18 . If circuit is okay, go to next step.
Check fuel pump speed control PWM circuit for poor connection to PCM or fuel pump control module. Check fuel pump control module ignition feed circuit for poor connection at fuel pump control module. Repair as necessary. After repairs, go to step 18 . If connections are okay, go to step 14 .
Turn ignition off. Reconnect PCM harness connector. Disconnect fuel pump control module. Turn ignition on. Using test light, connect test light between fuel pump speed control PWM circuit and ignition feed circuit at fuel pump control module harness connector. Using scan tool, cycle fuel pump PWM output on and off. If test light flashes on and off, go to step 16 . If test light does not flash on and off, go to next step.
Check fuel pump speed control PWM circuit for poor connection at PCM. Repair as necessary. After repairs, go to step 18 . If connection is okay, go to step 15 .
Locate and repair open in ignition feed circuit to fuel pump relay or between fuel pump relay and fuel pump control module. Repair as necessary. After repairs, go to step 18 .
Replace fuel pump control module. After replacing control module, go to step 18 .
Replace PCM. Program replacement PCM using required equipment. After replacing PCM, go to step 18 .
Check for poor connection at fuel pump relay. Repair as necessary. After repairs, go to step 18 . If connection is okay, go to next step.
Replace fuel pump relay. After replacing relay, 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 this DTC. If scan tool displays that this DTC FAILED THIS IGN, return to step 2 . If scan tool does not display that this DTC FAILED THIS IGN, repair is complete.

Check for faulty connections or damaged harness. Disconnect PCM connector. Turn ignition on. Connect a DVOM between engine ground and fuel pump speed control PWM circuit. Observe DVOM while moving all related harness and connectors. A change in voltage display indicates fault location.

DTC P1671: MIL CONTROL CIRCUIT (3.1L "N" & "W" BODIES & 3.4L "N" BODY)

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

Conditions required to set DTC are, ignition is on, improper voltage level detected on output circuit controlling MIL and conditions are present for at least 30 seconds.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(ref-132811-S27457185922002013000000) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Turn ignition off. Disconnect PCM harness connector. Turn ignition on. Using DVOM, check voltage between ground and MIL control circuit at PCM connector. If battery voltage is present, go to next step. If battery voltage is not present, go to step 6 .
Set ammeter to 10-amp range. Check current between ground and MIL control circuit at PCM connector. Monitor reading for a minimum of 2 minutes. If current is.05-.50 amp, go to step 11 . If current is not.05-.50 amp, go to next step.
Disconnect instrument panel cluster connector. Using DVOM, check voltage between ground and MIL control circuit at harness connector. If voltage reading is zero volts, go to step 10 . If voltage reading is not zero volts, go to next step.
Locate and repair short to voltage in MIL control circuit. After repairs, go to step 15 .
Check ignition feed fuse for instrument panel indicators. If fuse is blown, go to next step. If fuse is okay, go to step 8 .
Locate and repair short to ground in ignition feed circuit for instrument panel indicators. Replace fuse. After repairs, go to step 15 .
Disconnect instrument cluster connector. Turn ignition on. Check voltage between ground and ignition feed circuit for instrument cluster indicators. If battery voltage is present, go to next step. If battery voltage is not present, go to step 13 .
Check for an open or short to ground in MIL control circuit. Repair as necessary. After repairs, go to step 15 . If circuit is okay, go to next step.
Check MIL control circuit and ignition feed circuit for poor terminal connection at instrument cluster and at PCM connector. Repair as necessary. After repairs, go to step 15 . If connections are okay, diagnose instrument cluster assembly.
Turn ignition off. Reconnect PCM harness connector. Disconnect instrument cluster connector. Turn ignition on. Connect a test light between MIL control circuit and ignition feed circuit terminals at instrument panel connector. Using scan tool, select OUTPUTS TEST function and cycle MIL on and off. If test light flashes on and off, see «DIAGNOSTIC AIDS»(/gmc/savana/i-1996-2002/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p1537-u1193) . If test light does not flash, go to next step.
Check MIL control circuit for poor terminal connection at PCM. Repair as necessary. After repairs, go to step 15 . If connection is okay, go to step 14 .
Locate and repair open in ignition feed circuit to instrument cluster indicators. After repairs, go to step 15 .
Replace PCM. Program replacement PCM using required equipment. After replacing PCM, go to next step.
Using scan tool, select CLEAR INFO or CLEAR DTCs function to 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 this DTC until DTC test runs. If scan tool indicates FAILED THIS IGN, repeat step 2 . If scan tool does not indicate FAILED THIS IGN, repair is complete.

Check for faulty connections or damaged harness. Disconnect PCM harness connector. Turn ignition on. Connect DVOM between engine ground and MIL control circuit at PCM harness connector. Observe DVOM while moving all related harness and connectors. A change in voltage display indicates fault location.

DTC P1671: MIL CONTROL CIRCUIT (3.8L "C", "G", "H" & "W" BODIES)

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

Conditions required to set DTC are, ignition is on, improper voltage level detected on output circuit controlling MIL and conditions present for at least 30 seconds.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(ref-132811-S27457185922002013000000) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Turn ignition off. Disconnect PCM harness connector. Turn ignition on. Using DVOM, check voltage between ground and MIL control circuit at PCM connector. If battery voltage is present, go to next step. If battery voltage is not present, go to step 6 .
Set ammeter to 10-amp range. Check current between ground and MIL control circuit at PCM connector. Monitor reading for a minimum of 2 minutes. If current is.05-.50 amp, go to step 11 . If current is not.05-.50 amp, go to next step.
Disconnect instrument panel cluster connector. Using DVOM, check voltage between ground and MIL control circuit at harness connector. If voltage reading is zero volts, go to step 10 . If voltage reading is not zero volts, go to next step.
Locate and repair short to voltage in MIL control circuit. After repairs, go to step 15 .
Check ignition feed fuse for instrument panel indicators. If fuse is blown, go to next step. If fuse is okay, go to step 8 .
Locate and repair short to ground in ignition feed circuit for instrument panel indicators. Replace fuse. After repairs, go to step 15 .
Disconnect instrument cluster connector. Turn ignition on. Check voltage between ground and ignition feed circuit for instrument cluster indicators. If battery voltage is present, go to next step. If battery voltage is not present, go to step 13 .
Check for an open or short to ground in MIL control circuit. Repair as necessary. After repairs, go to step 15 . If circuit is okay, go to next step.
Check MIL control circuit and ignition feed circuit for poor terminal connection at instrument cluster and at PCM connector. Repair as necessary. After repairs, go to step 15 . If connections are okay, diagnose instrument cluster assembly.
Turn ignition off. Reconnect PCM harness connector. Disconnect instrument cluster connector. Turn ignition on. Connect a test light between MIL control circuit and ignition feed circuit terminals at instrument panel connector. Using scan tool, select OUTPUTS TEST function and cycle MIL on and off. If test light flashes on and off, see «DIAGNOSTIC AIDS»(/gmc/savana/i-1996-2002/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p1537-u1193) . If test light does not flash, go to next step.
Check MIL control circuit for poor terminal connection at PCM. Repair as necessary. After repairs, go to step 15 . If connection is okay, go to step 14 .
Locate and repair open in ignition feed circuit to instrument cluster indicators. After repairs, go to step 15 .
Replace PCM. Program replacement PCM using required equipment. After replacing PCM, go to next step.
Using scan tool, select CLEAR INFO or CLEAR DTCs function to 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 this DTC until DTC test runs. If scan tool indicates FAILED THIS IGN, repeat step 2 . If scan tool does not indicate FAILED THIS IGN, repair is complete.

DTC P1672: LOW OIL LEVEL LIGHT CONTROL CIRCUIT (3.8L "G" BODY)

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

Output Driver Modules (ODM) are used by PCM to turn on current-driven devices needed to control various engine and transaxle functions. Each ODM can control up to 7 outputs, including low engine oil level indicator driver circuit, by supplying ground to device PCM is commanding on. ODMs can diagnose each circuit individually. If ODM output (low engine oil level indicator driver circuit) detects an improper voltage level, DTC will set.

Conditions required to set DTC are, ignition is on, an improper voltage level has been detected on low engine oil level indicator driver circuit and conditions present for at least 30 seconds.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(ref-132811-S27457185922002013000000) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Turn ignition off. Disconnect PCM harness connector. Turn ignition on. Using a DVOM, check voltage between oil level switch control circuit at PCM harness connector and ground. If battery voltage is present, go to next step. If battery voltage is not present, go to step 6 .
Connect DVOM between oil level switch light control circuit at PCM harness connector and chassis ground. Monitor reading for 2 minutes. If DVOM reads.05-.50 amp, go to step 11 . If DVOM does not read.05-.50 amp, go to next step.
Turn ignition off. Disconnect instrument panel harness connector (leave PCM harness connector disconnected). Turn ignition on. Check voltage between low engine oil level light control circuit and ground. If voltage reading is zero volts, go to step 10 . If voltage reading is not zero volts, go to next step.
Locate and repair short to voltage in low engine oil level light control circuit. Repair as necessary. After repairs, go to step 15 .
Check ignition feed fuse for instrument panel indicators. If fuse is blown, go to next step. If use is not blown, go to step 8 .
Locate and repair short to ground in ignition feed circuit for instrument panel indicators. Replace fuse. After repairs, go to step 15 .
Disconnect instrument cluster harness connector. Turn ignition on. Check voltage between ignition feed circuit for instrument cluster indicators and ground. If battery voltage is present, go to next step. If battery voltage is not present, go to step 13 .
Check for open or short to ground in low oil level light control circuit. Repair as necessary. After repairs, go to step 15 . If circuit is okay, go to next step.
Check for poor terminal connections at instrument panel and PCM. Repair as necessary. After repairs, go to step 15 . If connections are okay, diagnose instrument panel assembly.
Turn ignition off. Reconnect PCM harness connector. Disconnect instrument cluster connector. Turn ignition on. Using a test light, connect test light between low engine oil level light control circuit and ignition feed circuit at instrument panel harness connector. Using scan tool, cycle the low engine oil level light on and off. If test light flashes on and off, see «DIAGNOSTIC AIDS»(/gmc/savana/i-1996-2002/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p1537-u1193) . If test light does not flash on and off, go to next step.
Check low engine oil level light control circuit for poor connection at PCM. Repair as necessary. After repairs, go to step 15 . If connection is okay, go to step 14 .
Locate and repair open in ignition feed circuit to instrument panel indicators. Repair as necessary. After repairs, go to step 15 .
Replace PCM. Program replacement PCM using required equipment. After replacing PCM, 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 this DTC. If scan tool displays that this DTC FAILED THIS IGN, return to step 2 . If scan tool does not display that this DTC FAILED THIS IGN, repair is complete.

Check for faulty connections or damaged harness. Disconnect PCM harness connector. Turn ignition on. Connect a DVOM between engine ground and PCM harness connector low engine oil level indicator driver circuit. Observe DVOM while moving all related harness and connectors. A change in voltage display indicates fault location.

DTC P1673: ENGINE HOT LIGHT CONTROL CIRCUIT (3.4L "U" SERIES)

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

Output Driver Modules (ODM) are used by PCM to turn on current-driven devices needed to control various engine and transaxle functions. Each ODM can control up to 7 outputs by supplying ground to device PCM is commanding on. ODMs can diagnose each circuit individually. If ODM "D" output 3 (ENGINE HOT light indicator driver circuit) detects an improper voltage level, DTC will set.

Conditions required to set DTC are, ignition is on, an improper voltage level has been detected on ENGINE HOT light indicator driver circuit and conditions present for at least 20 seconds.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(ref-132811-S27457185922002013000000) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Ensure engine coolant level is full. Turn ignition off. Disconnect PCM harness connector. Turn ignition on. Using a test light connected to battery voltage, probe ENGINE HOT light circuit at PCM harness connector. If test light illuminates, go to next step. If test light does not illuminate, go to step 6 .
Turn ignition off. Reconnect PCM harness connector. Check temperature gauge using scan tool. If gauge is indicating excessive temperature, check and repair temperature gauge circuit. If gauge does not indicate excessive temperature, go to next step.
Turn ignition on, with engine off. Using DVOM, check voltage to ENGINE HOT light circuit at PCM harness connector. If voltage reading is near battery voltage, go to step 6 . If voltage reading is not near battery voltage, go to next step.
Check ENGINE HOT light circuit for short to ground. Repair as necessary. After repairs, go to step 8 . If circuit is okay, go to step 7 .
Check for open in ignition feed circuit to ENGINE HOT light indicator. Check for poor terminal connection at PCM. Repair as necessary. After repairs, go to step 9 . If no problems were found, go to next step.
Replace PCM. Program replacement PCM using required equipment. After replacing PCM, go to step 9 .
Locate and repair short to ground at ENGINE HOT light circuit. 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 this DTC. If scan tool displays that this DTC FAILED THIS IGN, return to step 2 . If scan tool does not display that this DTC FAILED THIS IGN, repair is complete.

Check for faulty connections or damaged harness. Disconnect PCM harness connector. Turn ignition on. Connect a DVOM between engine ground and PCM harness connector ENGINE HOT light control circuit. Observe DVOM while moving all related harness and connectors. A change in voltage display indicates fault location.

DTC P1673: ENGINE HOT LIGHT CONTROL CIRCUIT (3.8L "G" BODY)

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

Output Driver Modules (ODM) are used by PCM to turn on current-driven devices needed to control various engine and transaxle functions. Each ODM can control up to 7 outputs by supplying ground to device PCM is commanding on. ODMs can diagnose each circuit individually. If ODM output (ENGINE HOT light indicator driver circuit) detects an improper voltage level, DTC will set.

Conditions required to set DTC are, ignition is on, an improper voltage level has been detected on ENGINE HOT light indicator driver circuit and conditions are present for at least 20 seconds.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(ref-132811-S27457185922002013000000) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Turn ignition off. Disconnect PCM harness connector. Turn ignition on. Check voltage between ground and ENGINE HOT light control circuit at PCM harness connector. If battery voltage is present, go to next step. If battery voltage is not present, go to step 6 .
Check current between ground and ENGINE HOT light control circuit at PCM harness connector. Monitor reading for at least 2 minutes. If current reads between.05-.50 amp, go to step 11 . If current does not read between.05-.50 amp, go to next step.
Turn ignition off. Disconnect instrument panel connector. Leave PCM connector disconnected. Turn ignition on. Check voltage between ground and ENGINE HOT control circuit. If DVOM reads zero volts, go to step 10 . If DVOM does not read zero volts, go to next step.
Locate and repair short to voltage in ENGINE HOT light control circuit. After repairs, go to step 15 .
Check ignition feed fuse for instrument panel indicators. If fuse is blown, go to next step. If fuse is okay, go to step 8 .
Locate and repair short to ground in ignition feed circuit for instrument panel indicators. Replace fuse. After repairs, go to step 15 .
Turn ignition off. Disconnect instrument cluster. Turn ignition on. Check voltage between ground and ignition feed circuit for instrument cluster indicators. If battery voltage is present, go to next step. If battery voltage is not present, go to step 13 .
Check ENGINE HOT light control circuit for open or short to ground. Repair as necessary. After repairs, go to step 15 . If circuit is okay, go to step 13 .
Check ENGINE HOT light control circuit and instrument panel indicators ignition feed circuit for poor connection at instrument panel and PCM. Repair as necessary. After repairs, go to step 15 . If connections are okay, diagnose or repair instrument panel. See appropriate INSTRUMENT PANELS article in ACCESSORIES & EQUIPMENT.
Turn ignition off. Reconnect PCM harness connector. Disconnect instrument cluster connector. Turn ignition on. Connect test light between ENGINE HOT light control circuit and ignition feed circuit at instrument panel harness connector. Using scan tool, cycle ENGINE HOT light on and off. If test light flashes on and off, see «DIAGNOSTIC AIDS»(/gmc/savana/i-1996-2002/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p1537-u1193) . If test light does not flash on and off, go to next step.
Check ENGINE HOT light control circuit for poor connection at PCM. Repair as necessary. After repairs, go to step 15 . If connection is okay, go to step 14 .
Locate and repair open in ignition feed control circuit to instrument panel indicators. After repairs, go to step 15 .
Replace PCM. Program replacement PCM using required equipment. After replacing PCM, 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 this DTC. If scan tool displays that this DTC FAILED THIS IGN, return to step 2 . If scan tool does not display that this DTC FAILED THIS IGN, repair is complete.

DTC P1676: EVAP PURGE VALVE CONTROL CIRCUIT (3.1L "N" & "W" BODIES & 3.4L "N" BODY)

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

Conditions required to set DTC are, ignition is on, improper voltage level detected on output circuit controlling EVAP purge solenoid valve and conditions are present for at least 30 seconds.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(ref-132811-S27457185922002013000000) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Turn ignition off. Disconnect PCM harness connector. Turn ignition on. Using DVOM, check voltage between ground and EVAP purge valve control circuit at PCM connector. If battery voltage is present, go to next step. If battery voltage is not present, go to step 6 .
Set ammeter to 10-amp range. Check current between ground and EVAP purge valve control circuit at PCM connector. Monitor reading for a minimum of 2 minutes. If current is.05-.50 amp, go to step 11 . If current is not.05-.50 amp, go to next step.
Disconnect EVAP purge valve connector. Using DVOM, check voltage between ground and EVAP purge valve control circuit at harness connector. If voltage reading is zero volts, go to step 10 . If voltage reading is not zero volts, go to next step.
Locate and repair short to voltage in EVAP purge valve control circuit. After repairs, go to step 16 .
Turn ignition off. Remove and inspect fuse for EVAP purge valve. If fuse is blown, go to next step. If fuse is okay, go to step 8 .
Locate and repair short to ground in ignition feed circuit for EVAP purge vent valve. Replace fuse. After repairs, go to step 16 .
Disconnect EVAP purge valve. Turn ignition on. Check voltage between ground and ignition feed circuit for EVAP purge valve harness connector. If battery voltage is present, go to next step. If battery voltage is not present, go to step 13 .
Check for an open or short to ground in EVAP purge valve control circuit. Repair as necessary. After repairs, go to step 16 . If circuit is okay, go to next step.
Check EVAP purge valve control circuit and ignition feed circuit for poor terminal connection at EVAP purge valve and at PCM connector. Repair as necessary. After repairs, go to step 16 . If connections are okay, go to step 14 .
Turn ignition off. Reconnect PCM harness connector. Disconnect EVAP purge valve connector. Turn ignition on. Connect a test light between EVAP purge valve control circuit and ignition feed circuit terminals at EVAP purge valve connector. Using scan tool, select OUTPUTS TEST function and cycle EVAP purge solenoid on and off. If test light flashes on and off, see «DIAGNOSTIC AIDS»(/gmc/savana/i-1996-2002/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p1537-u1193) . If test light does not flash, go to next step.
Check EVAP purge valve control circuit for poor terminal connection at PCM. Repair as necessary. After repairs, go to step 16 . If connection is okay, go to step 15 .
Locate and repair open in ignition feed circuit to EVAP purge valve. After repairs, go to step 16 .
Replace EVAP purge valve. After replacing valve, go to step 16 .
Replace PCM. Program replacement PCM using required equipment. After replacing PCM, go to next step.
Using scan tool, select CLEAR INFO or CLEAR DTCs function to 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 this DTC until this DTC test runs. If scan tool indicates FAILED THIS IGN, repeat step 2 . If scan tool does not indicate FAILED THIS IGN, repair is complete.

DTC P1689: TRACTION CONTROL DELIVERED TORQUE CONTROL CIRCUIT (3.8L "F" BODY)

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

The Electronic Brake and Traction Control Module (EBTCM) controls the Pulse Width Modulated (PWM) signal on the desired torque circuit while monitoring the wheel speed sensors to detect slippage. The PCM monitors the PWM signal and reduces engine torque as needed by retarding ignition timing, decreasing boost duty cycle, increasing air/fuel ratio, or in severe cases, shutting off up to 3 fuel injectors.

PCM sends a PWM signal to the EBTCM on the delivered torque circuit, informing the EBTCM of response made to the desired torque signal. A problem with the delivered torque circuit should cause DTC P1689 and ABS/TCS DTC 76 to set, and traction control disabled.

Conditions for setting this DTC are, improper voltage level has been detected on the output circuit which controls the traction control delivered torque output and condition present for at least 30 seconds.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(ref-132811-S27457185922002013000000) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Turn ignition off. Disconnect PCM harness connector. Turn ignition on, with engine off. Check voltage on delivered torque circuit at PCM harness connector. If battery voltage is present, go to next step. If battery voltage is not present, go to step 6 .
Using a DVOM, monitor current on delivered torque control circuit at PCM connector for at least 2 minutes. If DVOM reading is 1-500 milliamps, go to step 11 . If DVOM reading is not 1-500 milliamps, go to next step.
Turn ignition on. Check voltage between ground and delivered torque control circuit. If voltage reading is zero volts, go to step 10 . If voltage reading is not zero volts, go to next step.
Locate and repair short to voltage in delivered torque circuit. After repairs, go to step 16 .
Turn ignition off. Check ignition feed fuse for EBTCM. If fuse is open, go to next step. If fuse is okay, go to step 8 .
Locate and repair short to ground in ignition feed circuit. Replace fuse. After repairs, go to step 16 .
Disconnect EBTCM harness connector. Turn ignition on. Check voltage between ground and ignition feed circuit for EBTCM. If battery voltage is present, go to step. If battery voltage is not present, go to step 13 .
Check delivered torque control circuit for open or short to ground. Repair as necessary. After repairs, go to step 16 . If circuit is okay, go to next step.
Check delivered torque control circuit for poor connection to PCM or EBTCM. Repair as necessary. After repairs, go to step 16 . If connections are okay, go to step 14 .
Turn ignition off. Reconnect PCM and EBTCM harness connectors. Turn ignition on. Using a test light, connect test light between delivered torque control circuit and ignition feed circuit. Using scan tool, cycle delivered torque output on and off. If test light flashes on and off, see «DIAGNOSTIC AIDS»(/gmc/savana/i-1996-2002/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p1537-u1193) . If test light does not flash, go to next step.
Check delivered torque control circuit for poor connection at PCM. Repair as necessary. After repairs, go to step 16 . If connections are okay, go to step 15 .
Locate and repair open in ignition feed circuit to EBTCM. After repairs, go to step 16 .
Replace EBTCM. After replacing EBTCM, go to step 16 .
Replace PCM. Program replacement PCM using required equipment. After replacing PCM, go to next step.
Using scan tool, select CLEAR INFO or CLEAR DTCs function to 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 this DTC until this DTC test runs. If scan tool indicates that this DTC failed this ignition, repeat step 2 . If scan tool does not indicate that this DTC failed this ignition, system is okay.

Check for faulty connections or damaged harness. Observe DVOM while moving all related harness and connectors. A change in voltage display indicates fault location.

DTC P1689: DELIVERED TORQUE CIRCUIT FAULT (5.7L "Y" BODY)

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

The Electronic Brake and Traction Control Module (EBTCM) supplies 12 volts on the delivered torque circuit to the PCM. PCM toggles this 12 volt signal to ground in order to produce a duty cycle signal. The signal is proportional to the amount of engine output torque reduction. In order to reduce engine output torque, PCM reduces the amount of spark advance and in some cases the PCM disables a number of fuel injectors. This diagnostic will test for a delivered torque signal failure. DTC will set when PCM does not receive the delivered torque signal for 3 seconds.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(ref-132811-S27457185922002013000000) 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, check for any ABS/Traction Control DTCs. If related DTCs are set, diagnose affected DTC(s). If no related DTC(s) are set, go to next step.
Turn ignition off. Disconnect PCM harness connector. Turn ignition on, with engine off. Check voltage on delivered torque circuit at PCM harness connector. If battery voltage is present, go to step 7 . If battery voltage is not present, go to next step.
Disconnect EBTCM harness connector. Check continuity of delivered torque circuit. If continuity exists, go to next step. If continuity does not exist, go to step 6 .
Check continuity of delivered torque circuit to ground. If continuity exists, go to next step. If continuity does not exist, diagnose ABS brake system. See appropriate ANTI-LOCK article in BRAKES.
Repair delivered torque circuit for an open or short to ground. After repairs, go to step 9 .
Check for poor connections at PCM. Repair as necessary. After repairs, go to step 9 . If connections are okay, go to next step.
Using scan tool, select CLEAR INFO or CLEAR DTCs function to 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 this DTC until this DTC test runs. If scan tool indicates FAILED THIS IGN, repeat step 2 . If scan tool does not indicate FAILED THIS IGN, repair is complete.
Using scan tool, select CAPTURE INFO, REVIEW INFO function. If any undiagnosed DTCs are displayed, diagnose affected DTCs.

Check for faulty connections or damaged harness. Observe DVOM while moving all related harness and connectors. A change in voltage display indicates fault location.

DTC will set if there is an engine torque limitation caused by traction control system, transmission or engine speed limitation, or engine output torque exceeds a certain value for 600 seconds.

DTC will turn off MIL after 3 consecutive drive trips that the diagnostic runs and passes. A history DTC clears after 40 consecutive warm-up cycles in which no failures are reported by this diagnostic or any other emission related diagnostic or battery is disconnected.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(ref-132811-S27457185922002013000000) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
If other DTCs are set, diagnose affected DTCs. If no other DTCs are set, go to next step.
Replace ECM. Program replacement ECM using required equipment. After replacing ECM, go to next step.
Using scan tool, select CLEAR INFO or CLEAR DTCs function to 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 this DTC until this DTC test runs. If scan tool indicates FAILED THIS IGN, repeat step 2 . If scan tool does not indicate FAILED THIS IGN, repair is complete.
Using scan tool, select CAPTURE INFO, REVIEW INFO function. If any undiagnosed DTCs are displayed, diagnose affected DTCs.

DTC U1000: NO CLASS II COMMUNICATION-ID NOT LEARNED (2.2L "S" SERIES & 2.4L "N" BODY)

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

A Class II serial data communications system is used to allow various modules to communicate and share information with each other. If a module cannot respond to PCM, DTC will set.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(ref-132811-S27457185922002013000000) 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, check if data from PCM can be displayed. If scan tool can display PCM data, go to next step. If scan tool cannot display PCM data, diagnose Data Link Connector (DLC).
Using scan tool, attempt to communicate with EBCM. If scan tool communicates with EBCM, go to next step. If scan tool does not communicate with EBCM, diagnose electrical system.
Using scan tool, attempt to communicate with BFC or TBC (trucks). If scan tool communicates with BFC or TBC, go to next step. If scan tool does not communicate with BFC or TBC, diagnose electrical system.
Using scan tool, check for additional DTCs or communication with other modules. Diagnose and repair as necessary. After repairs, go to next step.
Using scan tool, select CLEAR INFO or CLEAR DTCs function to 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 this DTC until this DTC test runs. If scan tool indicates FAILED THIS IGN, repeat step 2 . If scan tool does not indicate FAILED THIS IGN, go to next step.
Using scan tool, select CAPTURE INFO, REVIEW INFO function. If any undiagnosed DTCs are displayed, diagnose affected DTCs.

Check for damaged pins, corrosion and loose wires. An intermittent problem can be caused 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 U1016: SERIAL COMMUNICATIONS MALFUNCTION (2.2L & 2.4L "J" & "N" BODIES)

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

UART serial data communications system is used to allow various modules to communicate and share information with each other. The serial data communication circuit is connected to the PCM, EBCM, Diagnostic Energy Reserve Module (DERM) and Instrument Panel Cluster (IPC).

The IPC is the master of this network and sends out an updated information requests from other modules through the serial data circuit. Each module responds back to the IPC with updated information. PCM communicates with EBCM through the IPC over the serial data circuit. DTC will set when any of the modules cannot respond to each other or PCM does not receive 25 valid responses from IPC.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(ref-132811-S27457185922002013000000) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Turn ignition on, with engine off. Observe instrument panel and check if COOLANT indicator light is illuminates. If indicator light is illuminated, go to next step. If indicator light is not illuminated, go to step 9 .
Using scan tool, check if scan tool communicates with IPC. If scan tool communicates with IPC, go to next step. If scan tool does not communicate with IPC, go to step 5 .
Check for open in UART serial data circuit. Repair as necessary. After repairs, go to step 9 . If circuit is okay, go to step 6 .
Check for short to ground or voltage in UART serial data circuit. Repair as necessary. After repairs, go to step 9 . If circuit is okay, go to step 7 .
Check for poor connection at PCM connector. Repair as necessary. After repairs, go to step 9 . If connection is okay, go to step 8 .
Turn ignition off. Disconnect PCM harness connector. Turn ignition on. Using scan tool, attempt to communicate with IPC. If scan tool communicates with IPC, go to next step. If scan tool does not communicate with IPC, diagnose Data Link Connector (DLC) circuit.
Replace PCM. Program replacement PCM using required equipment. After replacing PCM, go to next step.
Using scan tool, select CLEAR INFO or CLEAR DTCs function to 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 this DTC until this DTC test runs. If scan tool indicates that this test failed in this ignition, repeat step 2 . If scan tool does not indicate that this test failed in this ignition, go to next step.
Using scan tool, select CAPTURE INFO, REVIEW INFO function. If any undiagnosed DTCs are displayed, diagnose affected DTCs.

Move/wiggle PCM and IPC connectors while watching IPC serial data. IPC indicator lights will illuminate when serial data is lost. Check for intermittent problem caused by electrical interference on IPC ground circuit. Check for poor connection, rubbed-through wire insulation or a broken wire inside insulation. Check for faulty or damaged terminal connections. Install an additional ground from IPC to battery negative terminal is electrical interference is suspected.

DTC U1026: LOSS OF ATCM COMMUNICATION (4.3L "S" & "T" SERIES)

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

A Class II serial data communications system is used to allow various modules to communicate and share information with each other. DTC will set when VCM does not receive an identifier message from EBCM or if a module cannot respond to VCM.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(ref-132811-S27457185922002013000000) 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, attempt to establish communications with Active Transfer Case Control Module (ATCM). If scan tool communicates with ATCM, go to next step. If scan tool does not communicate with ATCM, diagnose ATCM. See appropriate ELECTRONIC CONTROLS article in AUTOMATIC TRANSMISSIONS.
Check for open, short to ground or short to voltage in Class II serial data circuit between ATCM and VCM. Check for damaged terminals at DLC, VCM and ATCM. Repair as necessary. After repairs, go to step 7 . If circuits or terminals are okay, go to next step.
Turn ignition off. Reconnect all disconnected components. Using scan tool, clear DTCs. Turn ignition off for 15 seconds. Turn ignition on, with engine off. Check if this DTC resets. If DTC resets, go to next step. If DTC does not reset, go to step 6 .
Replace VCM. Program replacement VCM using required equipment and then perform Crankshaft Variation Learn Procedure. See DTC P1336. After performing learn procedures, go to step 7 .
This DTC is intermittent. Check if additional DTCs are set. Diagnose affected DTCs. If no additional DTCs are set, see «DIAGNOSTIC AIDS»(/gmc/savana/i-1996-2002/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p1537-u1193) .
Turn ignition off. Reconnect all disconnected components. Using scan tool, clear DTCs. Check if any DTC(s) resets. If DTC(s) resets, repeat step 1) . If DTC(s) does not reset, system is okay.

Do not clear DTCs unless directed by diagnostic procedure. Clearing DTCs will clear valuable Freeze Frame and Failure Records information.

Check for damaged pins, corrosion and loose wires. An intermittent problem can be caused by poor connection, rubbed-through wire insulation or broken wire inside insulation. Reviewing FAILURE RECORDS vehicle mileage since last diagnostic test may help determine how often condition that caused DTC to set occurs.

DTC U1026: LOSS OF ATCM COMMUNICATION (4.3L, 5.0L & 5.7L "C" & "K" 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»(ref-132811-S27457185922002013000000) 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, attempt to establish communications with Active Transfer Case Control Module (ATCM). If scan tool communicates with ATCM, go to next step. If scan tool does not communicate with ATCM, diagnose ATCM. See appropriate ELECTRONIC CONTROLS article in AUTOMATIC TRANSMISSIONS.
Check for open, short to ground or short to voltage in Class II serial data circuit between ATCM and VCM. Check for damaged terminals at DLC, VCM and ATCM. Repair as necessary. After repairs, go to step 7 . If circuits or terminals are okay, go to next step.
Turn ignition off. Reconnect all disconnected components. Using scan tool, clear DTCs. Turn ignition off for 15 seconds. Turn ignition on, with engine off. Check if this DTC resets. If DTC resets, go to next step. If DTC does not reset, go to step 6 .
Replace VCM. Program replacement VCM using required equipment and then perform Crankshaft Variation Learn Procedure. See DTC P1336. After performing learn procedures, go to step 7 .
This DTC is intermittent. Check if additional DTCs are set. Diagnose affected DTCs. If no additional DTCs are set, see «DIAGNOSTIC AIDS»(/gmc/savana/i-1996-2002/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p1537-u1193) .
Turn ignition off. Reconnect all disconnected components. Using scan tool, clear DTCs. Check if any DTC(s) resets. If DTC(s) resets, repeat step 1 . If DTC(s) does not reset, system is okay.

Do not clear DTCs unless directed by diagnostic procedure. Clearing DTCs will clear valuable Freeze Frame and Failure Records information.

DTC U1026: LOSS OF ATC CLASS II COMMUNICATION (6.5L "C" & "K" SERIES)

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

PCM monitors the Class II serial data circuit for communications from the Automatic Transfer Case (ATC) controller. If ATC controller is not communicating with PCM, DTC will set.

Before clearing DTCs, record FREEZE FRAME and FAILURE RECORDS information for reference. Perform On-Board Diagnostic (OBD) system check. See ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, diagnose ATC controller. See appropriate ELECTRONIC CONTROLS article in AUTOMATIC TRANSMISSIONS.

DTC will not set unless PCM and ATC controllers have already established communications first. This DTC will only diagnose an open or intermittent connection from ATC controller to splice.

DTC U1040: LOSS OF EBCM/EBTCM COMMUNICATION (2.4L "N" BODY - MALIBU)

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»(ref-132811-S27457185922002013000000) 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, check if scan tool can display data from PCM. If data can be displayed, go to next step. If data cannot be displayed , diagnose DLC.
Check for intermittent short or open in serial data circuit to EBCM. Repair as necessary. After repairs, go to step 6 . If circuit is okay, go to next step.
Check for intermittent short or open in serial data circuit to BFC. Repair as necessary. After repairs, go to step 6 . If circuit is okay, go to next step.
Check if additional DTCs are set. Diagnose affected DTCs. After repairs, go to next step.
Using scan tool, select CLEAR INFO or CLEAR DTCs function to 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 this DTC until this DTC test runs. If scan tool indicates that this test failed in this ignition, repeat step 2 . If scan tool does not indicate that this test failed in this ignition, go to next step.
Check for additional DTCs. Diagnose affected DTCs. If no other DTCs are set, see «DIAGNOSTIC AIDS»(/gmc/savana/i-1996-2002/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p1537-u1193) .

Attempting to start vehicle by by-passing the Passlock® II system or by substituting part without performing Password Learn procedures will set DTC P1631 and P1632.

DTC U1041: LOSS OF EBCM COMMUNICATION (2.2L "S" SERIES)

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

A Class II serial data communications system is used to allow various modules to communicate and share information with each other. DTC will set when module cannot respond to VCM.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(ref-132811-S27457185922002013000000) 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, check if scan tool can display data from PCM. If data can be displayed, go to next step. If data cannot be displayed , diagnose Data Link Connector (DLC) circuit.
Using scan tool, check if scan tool can display EBCM data. If data can be displayed, go to next step. If data cannot be displayed, diagnose electrical system.
Check for intermittent short or open in serial data circuit to BFC. Repair as necessary. After repairs, go to step 6 . If circuit is okay, go to next step.
Using scan tool, check for additional DTCs or communication with other modules. Diagnose or repair as necessary. After repairs, go to next step.
Using scan tool, select CLEAR INFO or CLEAR DTCs function to 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 this DTC until this DTC test runs. If scan tool indicates that this test failed in this ignition, repeat step 2 . If scan tool does not indicate that this test failed in this ignition, go to next step.
Check for additional DTCs. Diagnose affected DTCs. If no other DTCs are set, see «DIAGNOSTIC AIDS»(/gmc/savana/i-1996-2002/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p1537-u1193) .

DTC U1041: LOSS OF EBCM COMMUNICATION (4.3L "L", "M", "S" & "T" SERIES)

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

A Class II serial data communications system is used to allow various modules to communicate and share information with each other. DTC will set when module cannot respond to VCM.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(ref-132811-S27457185922002013000000) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Using scan tool, check if scan tool communicates with EBCM. If scan tool communicates with EBCM, go to next step. If scan tool does not communicate with EBCM, see appropriate ANTI-LOCK article in BRAKES.
Using scan tool, select EBCM function. Check if DTC U1041 is stored in ATC memory. If DTC is stored, see appropriate ANTI-LOCK article in BRAKES. If DTC U1041 is not set, go to next step.
Check for short or open in Class II serial data circuit between VCM and ATC. Check for faulty connections at DLC, VCM or ATC. Repair as necessary. After repairs, go to step 8 . If circuit or connections are okay, go to next step.
Reconnect all previously disconnected components. Using scan tool, clear DTCs. Turn ignition off for 15 seconds. Turn ignition on, with engine off. Check if DTC resets. If DTC resets, go to next step. If DTC does not reset, go to step 7 .
Replace VCM. Program VCM using required equipment and perform VTD and Crankshaft Variation Learn Procedure. After replacing VCM, go to next step.
DTC is intermittent. Check for additional DTCs. If additional DTCs are set, diagnose affected DTCs. If no additional DTCs are set, system is okay. See «DIAGNOSTIC AIDS»(/gmc/savana/i-1996-2002/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p1537-u1193) .
Turn ignition off. Reconnect all previously disconnected components. Using scan tool, clear all DTCs. Check if DTC resets. If DTC resets, repeat step 1) . If DTC does not reset, system is okay.

Do not clear DTCs unless directed by a diagnostic procedure. Clearing DTCs will also clear valuable Freeze Frame and Failure Records information.

DTC U1041: LOSS OF EBCM COMMUNICATION (4.3L, 5.0L & 5.7L "C", "G", "K" & "P" SERIES)

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

A Class II serial data communications system is used to allow various modules to communicate and share information with each other. DTC will set when module cannot respond to VCM.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(ref-132811-S27457185922002013000000) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article.. After performing OBD system check, go to next step.
Using scan tool, check if scan tool communicates with EBCM. If scan tool communicates with EBCM, go to next step. If scan tool does not communicate with EBCM, see appropriate ANTI-LOCK article in BRAKES.
Using scan tool, select EBCM function. Check if DTC U1041 is stored in ATC memory. If DTC is stored, see appropriate ANTI-LOCK article in BRAKES. If DTC U1041 is not set, go to next step.
Check for short or open in Class II serial data circuit between VCM and ATC. Check for faulty connections at DLC, VCM or ATC. Repair as necessary. After repairs, go to step 8 . If circuit or connections are okay, go to next step.
Reconnect all previously disconnected components. Using scan tool, clear DTCs. Turn ignition off for 15 seconds. Turn ignition on, with engine off. Check if DTC resets. If DTC resets, go to next step. If DTC does not reset, go to step 7 .
Replace VCM. Program VCM using required equipment and perform VTD and Crankshaft Variation Learn Procedure. After replacing VCM, go to next step.
DTC is intermittent. Check for additional DTCs. If additional DTCs are set, diagnose affected DTCs. If no additional DTCs are set, system is okay. See «DIAGNOSTIC AIDS»(/gmc/savana/i-1996-2002/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p1537-u1193) .
Turn ignition off. Reconnect all previously disconnected components. Using scan tool, clear all DTCs. Check if DTC resets. If DTC resets, repeat step 1) . If DTC does not reset, system is okay.

Do not clear DTCs unless directed by a diagnostic procedure. Clearing DTCs will also clear valuable Freeze Frame and Failure Records information.

DTC U1064: LOSS OF BCM/TBC/VTD COMMUNICATION (2.2L "S" SERIES & 2.4L "N" BODY - MALIBU)

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

A Class II serial data communications system is used to allow various modules to communicate and share information with each other. DTC will set when module cannot respond to PCM.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(ref-132811-S27457185922002013000000) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Using scan tool, check if scan tool can display data from PCM. If PCM data can be displayed, go to next step. If PCM cannot be displayed, diagnose Data Link Connector (DLC) circuit.
Using scan tool check if scan tool can display data from BCM, TBC or VTD data. If data can be displayed, go to next step. If data cannot be displayed, diagnose electrical system.
Check for intermittent short or open in serial data circuit to BFC. Repair as necessary. After repairs, go to step 6 . If circuit is okay, go to next step.
Using scan tool, check for additional DTCs or communication with other modules. Diagnose or repair as necessary. After repairs, go to next step.
Using scan tool, clear DTCs. Start and warm engine to normal operating temperature. Operate vehicle within conditions within conditions for setting this DTC. If scan tool indicates that this diagnostic ran and passed, go to next step. If scan tool does not indicate that this diagnostic ran and passed, repeat step 2 .
Check for additional DTCs. If additional DTCs are set, diagnose affected DTCs. If no additional DTCs are set, system is okay. See «DIAGNOSTIC AIDS»(/gmc/savana/i-1996-2002/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p1537-u1193) .

Check for damaged pins, corrosion and loose wires. An intermittent problem can be caused by poor connection, rubbed-through wire insulation or broken wire inside insulation. Install additional ground wire from IPC to negative battery terminal is electrical interference is suspected.

DTC U1064: LOSS OF BCM/VTD COMMUNICATION (4.3L "S" & "T" SERIES)

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

A Class II serial data communications system is used to allow various modules to communicate and share information with each other. DTC will set when module cannot respond to VCM.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(ref-132811-S27457185922002013000000) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Using scan tool, check if scan tool can display data from BCM. If BCM data can be displayed, go to next step. If BCM cannot be displayed, diagnose Data Link Connector (DLC) circuit.
Using scan tool, check if scan tool can display BCM or VTD data. If data can be displayed, go to next step. If data cannot be displayed, diagnose electrical system.
Check for intermittent short or open in serial data circuit to BFC. Repair as necessary. After repairs, go to step 6 . If circuit is okay, go to next step.
Using scan tool, check for additional DTCs or communication with other modules. Diagnose or repair as necessary. After repairs, go to next step.
Using scan tool, clear DTCs. Start and warm engine to normal operating temperature. Operate vehicle within conditions within conditions for setting this DTC. If scan tool indicates that this diagnostic ran and passed, go to next step. If scan tool does not indicate that this diagnostic ran and passed, repeat step 2 .
Check for additional DTCs. If additional DTCs are set, diagnose affected DTCs. If no additional DTCs are set, system is okay. See «DIAGNOSTIC AIDS»(/gmc/savana/i-1996-2002/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p1537-u1193) .

DTC U1064: LOSS OF BCM/VTD COMMUNICATION (4.8L "C" & "K" SERIES)

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

A Class II serial data communications system is used to allow various modules to communicate and share information with each other. DTC will set when module cannot respond to VCM.

Perform On-Board Diagnostic (OBD) system check. See ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, perform SCAN TOOL DOES NOT COMMUNICATE WITH CLASS 2 DATA LINE. Refer to BODY CONTROL MODULES article in ACCESSORIES & EQUIPMENT.

The communication DTCs are for information only. This DTC will not set unless the modules have already established communications.

DTC U1192: LOSS OF EVO/VTD PASSLOCK® COMMUNICATION (4.3L "L" & "M" SERIES)

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

A Class II serial data communications system is used to allow various modules to communicate and share information with each other. DTC will set when module cannot respond to VCM.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(ref-132811-S27457185922002013000000) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Using scan tool, check if scan tool can communicate with Vehicle Theft Deterrent (VTD) system. If scan tool can communicate with VTD, go to next step. If scan tool cannot communicate with VTD, see appropriate ANTI-THEFT SYSTEMS article in ACCESSORIES & EQUIPMENT.
Using scan tool, select Active Transfer Case (ATC) function. Check if DTC is stored in ATC memory. If DTC is stored, see appropriate ANTI-THEFT SYSTEMS article in ACCESSORIES & EQUIPMENT. If DTC is not stored, go to next step.
Check for short or open in Class II serial data circuit between VCM and VTD. Check for faulty connections at DLC, VCM or ATC. Repair as necessary. After repairs, go to step 6 . If circuit is okay, go to next step.
Reconnect all previously disconnected components. Using scan tool, clear DTCs. Turn ignition off for 15 seconds. Turn ignition on, with engine off. Check if DTC resets. If DTC resets, go to step 8 . If DTC does not reset, go to step 7 .
Repair as necessary. After repairs, go to step 9 .
DTC is intermittent. Check for additional DTCs. If additional DTCs are set, diagnose affected DTCs. If no additional DTCs are set, system is okay. See «DIAGNOSTIC AIDS»(/gmc/savana/i-1996-2002/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p1537-u1193) .
Replace VCM. Program replacement VCM using required equipment and perform VTD and Crankshaft Variation Learn Procedure. After replacing VCM, go to next step.
Turn ignition off. Reconnect all previously disconnected components. Using scan tool, clear DTCs. Turn ignition off for 15 seconds. Turn ignition on, with engine off. Check if DTC resets. If DTC resets, go to step 1) . If DTC does not reset, system is okay.

Do not clear DTCs unless directed by a diagnostic procedure. Clearing DTCs will also clear valuable Freeze Frame and Failure Records information.

DTC U1192: LOSS OF EVO/VTD PASSLOCK® COMMUNICATION (4.3L, 5.0L & 5.7L "C", "G" & "K" SERIES)

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

A Class II serial data communications system is used to allow various modules to communicate and share information with each other. DTC will set when module cannot respond to VCM.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(ref-132811-S27457185922002013000000) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Using scan tool, check if scan tool can communicate with Vehicle Theft Deterrent (VTD) system. If scan tool can communicate with VTD, go to next step. If scan tool cannot communicate with VTD, see appropriate ANTI-THEFT SYSTEMS article in ACCESSORIES & EQUIPMENT.
Using scan tool, select Active Transfer Case (ATC) function. Check if DTC is stored in ATC memory. If DTC is stored, see appropriate ANTI-THEFT SYSTEMS article in ACCESSORIES & EQUIPMENT. If DTC is not stored, go to next step.
Check for short or open in Class II serial data circuit between VCM and VTD. Check for faulty connections at DLC, VCM or ATC. Repair as necessary. After repairs, go to step 6 . If circuit is okay, go to next step.
Reconnect all previously disconnected components. Using scan tool, clear DTCs. Turn ignition off for 15 seconds. Turn ignition on, with engine off. Check if DTC resets. If DTC resets, go to step 8 . If DTC does not reset, go to step 7 .
Repair as necessary. After repairs, go to step 9 .
DTC is intermittent. Check for additional DTCs. If additional DTCs are set, diagnose affected DTCs. If no additional DTCs are set, system is okay. See «DIAGNOSTIC AIDS»(/gmc/savana/i-1996-2002/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p1537-u1193) .
Replace VCM. Program replacement VCM using required equipment and perform VTD and Crankshaft Variation Learn Procedure. After replacing VCM, go to next step.
Turn ignition off. Reconnect all previously disconnected components. Using scan tool, clear DTCs. Turn ignition off for 15 seconds. Turn ignition on, with engine off. Check if DTC resets. If DTC resets, go to step 1) . If DTC does not reset, system is okay.

Do not clear DTCs unless directed by a diagnostic procedure. Clearing DTCs will also clear valuable Freeze Frame and Failure Records information.

DTC U1192: LOSS OF EVO/VTD PASSLOCK® COMMUNICATION (6.5L "C" & "K" SERIES)

Note. For circuit reference, see WIRING DIAGRAM article.

PCM monitors the Class II serial data circuit for communications from the EVO/Passlock® controller. DTC will set when controller is not communicating with PCM or no serial data is present between controller to PCM.

Before clearing DTCs, record Freeze Frame and Failure Records information for reference. Perform On-Board Diagnostic (OBD) system check. See ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, diagnose EVO/Passlock® controller. See appropriate ANTI-THEFT SYSTEMS article in ACCESSORIES & EQUIPMENT.

DTC will not set unless PCM and ATC controllers have already established communications first. This DTC will only diagnose an open or intermittent connection from the EVO/Passlock® controller to splice.

DTC U1192: LOSS OF EVO/PASSLOCK® COMMUNICATION (6.5L "G" SERIES)

Note. For circuit reference, see WIRING DIAGRAM article.

PCM monitors the Class II serial data circuit for communications from the EVO/Passlock® controller. If controller is not communicating with PCM, DTC will set.

Before clearing DTCs, record Freeze Frame and Failure Records information for reference. Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(ref-132811-S27457185922002013000000) 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 DIAGNOSTIC CIRCUIT CHECK and CLASS II MESSAGE MONITOR. If scan tool displays EVO/Passlock® active, go to next step. If scan tool displays that controller is not active, go to step 4 .
DTC is intermittent. If no additional DTCs are set, see «DIAGNOSTIC AIDS»(/gmc/savana/i-1996-2002/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p1537-u1193) . If additional DTCs are set, diagnose affected DTCs.
Check Class II serial data circuit from EVO/Passlock® controller to splice for open circuit or proper connection to controller. Repair as necessary. After repairs, go to next step. If circuit or connection is okay, diagnose EVO/Passlock® system. See appropriate ANTI-THEFT SYSTEMS article in ACCESSORIES & EQUIPMENT.
Clear DTCs using scan tool. Warm engine to normal operating temperature. Using scan tool, select DTC, SPECIFIC then enter this DTC. Operate vehicle within conditions for setting this DTC. If scan tool indicates that this diagnostic passed, go to next step. If scan tool does not indicate that this diagnostic passed, repeat step 2 .
Check if additional DTCs are set. Diagnose affected DTCs. If no additional DTCs are set, system is okay.

DTC U1193: LOSS OF VIM COMMUNICATION (4.3L, 5.0L & 5.7L "C", "G" & "K" SERIES)

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

A Class II serial data communications system is used to allow various modules to communicate and share information with each other. DTC will set when module cannot respond to VCM.

Perform On-Board Diagnostic (OBD) system check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(ref-132811-S27457185922002013000000) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
Using scan tool, check if scan tool can communicate with Vehicle Immobilizer Module (VIM). If scan tool can communicate with VIM, go to next step. If scan tool cannot communicate with VIM, see appropriate ANTI-THEFT SYSTEMS article in ACCESSORIES & EQUIPMENT.
Using scan tool, select Active Transfer Case (ATC) function. Check if DTC is stored in ATC memory. If DTC is stored, see appropriate ANTI-THEFT SYSTEMS article in ACCESSORIES & EQUIPMENT. If DTC is not stored, go to next step.
Check for short or open in Class II serial data circuit between VCM and VTD. Check for faulty connections at DLC, VCM or ATC. Repair as necessary. After repairs, go to step 6 . If circuit is okay, go to next step.
Reconnect all previously disconnected components. Using scan tool, clear DTCs. Turn ignition off for 15 seconds. Turn ignition on, with engine off. Check if DTC resets. If DTC resets, go to step 8 . If DTC does not reset, go to step 7 .
Repair as necessary. After repairs, go to step 9 .
DTC is intermittent. Check for additional DTCs. If additional DTCs are set, diagnose affected DTCs. If no additional DTCs are set, system is okay. See «DIAGNOSTIC AIDS»(/gmc/savana/i-1996-2002/remont/testing-diagnostics/#engine-control-system-tests-wcodes-dtc-p1537-u1193) .
Replace VCM. Program replacement VCM using required equipment and perform VTD and Crankshaft Variation Learn Procedure. After replacing VCM, go to next step.
Turn ignition off. Reconnect all previously disconnected components. Using scan tool, clear DTCs. Turn ignition off for 15 seconds. Turn ignition on, with engine off. Check if DTC resets. If DTC resets, repeat step 1) . If DTC does not reset, system is okay.

Do not clear DTCs unless directed by a diagnostic procedure. Clearing DTCs will also clear valuable Freeze Frame and Failure Records information.

DTC U1301: CLASS 2 COMMUNICATION CIRCUIT - HIGH VOLTAGE (4.8L "C" & "K" SERIES)

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

The class 2 circuit connects to various modules. These modules monitor the link for serial data communications during normal vehicle operation. Operating information and commands are exchanged among the modules on the data link. When a module receives a critical operating parameter from another module, the receiving module records the identification number from the module that sent the message. This is called State of Health Monitoring (SOH). A critical operating command will have the sending module's identification number attached with it. Once an identification number is learned by a module, it will continue to monitor for that number. When no message is detected from a learned identification number for a set time, a code is set in the module that was monitoring the identification number.

Perform On-Board Diagnostic (OBD) system check. See ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, perform SCAN TOOL DOES NOT COMMUNICATE WITH CLASS 2 DATA LINE. Refer to BODY CONTROL MODULES article in ACCESSORIES & EQUIPMENT.

This DTC cannot be displayed on a scan tool when the fault is active. The scan tool will not communicate with an active DTC U1301. The communication DTCs are for information only.

See also:
• DIAGNOSTIC AIDS
• DIAGNOSTIC AIDS
• DIAGNOSTIC AIDS

Engine Control System - Tests W/codes - DTC p1537-u1193 GMC Savana I

MODEL IDENTIFICATION

DTC P1537: A/C REQUEST CIRCUIT LOW VOLTAGE (4.0L "G" BODY)

Circuit Description

Diagnostic Procedures

Diagnostic Aids

DTC P1538: A/C REQUEST CIRCUIT HIGH VOLTAGE (4.0L "G" BODY)

DTC P1539: A/C CLUTCH STATUS CIRCUIT VOLTAGE HIGH (5.7L "F" & "Y" BODIES)

DTC P1540: A/C SYSTEM-HIGH PRESSURE (4.0L "G" BODY)

DTC P1542: A/C SYSTEM HIGH PRESSURE/HIGH TEMPERATURE (4.0L "G" BODY)

DTC P1545: A/C CLUTCH RELAY CONTROL CIRCUIT (3.0L "V" BODY)

DTC P1546: A/C CLUTCH RELAY CIRCUIT FAULT (3.4L "U" SERIES)

DTC P1546: A/C CLUTCH RELAY CIRCUIT FAULT (3.8L "F"BODY)

DTC P1546: A/C CLUTCH STATUS CIRCUIT VOLTAGE LOW (5.7L "F" & "Y" BODIES)

DTC P1554: CRUISE CONTROL STATUS CIRCUIT (3.1L "N" & "W" BODIES & 3.4L "N" BODY & "U" SERIES)

DTC P1554: CRUISE ENGAGED CIRCUIT HIGH VOLTAGE (3.5L "W" BODY)

DTC P1554: CRUISE CONTROL STATUS CIRCUIT (3.8L "C", "G", "H" & "W" BODIES)

DTC P1554: CRUISE ENGAGED CIRCUIT HIGH VOLTAGE (4.0L "G" BODY)

DTC P1554: CRUISE ENGAGED CIRCUIT HIGH VOLTAGE (4.6L "E" & "K" BODIES - DEVILLE & ELDORADO)

DTC P1554: CRUISE CONTROL FEEDBACK CIRCUIT (4.6L "K" BODY - SEVILLE)

DTC P1555: EVO CIRCUIT FAULT (1.9L SATURN - DOHC)

DTC P1560: CRUISE CONTROL-TRANSAXLE NOT IN DRIVE (4.0L "G" BODY)

DTC P1560: TRANSAXLE NOT IN DRIVE-CRUISE CONTROL DISABLED (4.6L "K" BODY - SEVILLE)

DTC P1564: VEHICLE ACCELERATION TOO HIGH-CRUISE CONTROL DISABLED (4.0L "G" BODY & 4.6L "E" & "K" BODIES)

DTC P1566: ENGINE RPM TOO HIGH-CRUISE CONTROL DISABLED (4.0L "G" BODY & 4.6L "E" & "K" BODIES)

DTC P1567: CRUISE CONTROL DISABLED-ABCS ACTIVE (4.0L "G" BODY & 4.6L "K" BODY - SEVILLE)

DTC P1570: TRACTION CONTROL ACTIVE-CRUISE CONTROL DISABLED (4.0L "G" BODY & 4.6L "E" & "K" BODIES)

DTC P1571: TCS DESIRED TORQUE CIRCUIT (3.4L "U" SERIES)

DTC P1571: TCS DESIRED TORQUE CIRCUIT (3.5L "W" BODY)

DTC P1571: TCS DESIRED TORQUE CIRCUIT (3.8L "C", "G", "H" & "W" BODIES)

DTC P1571: TCS DESIRED TORQUE CIRCUIT (3.8L "F" BODY)

DTC P1571: TCS PULSE WIDTH MODULATED (PWM) CIRCUIT NO FREQUENCY (4.0L "G" BODY)

DTC P1571: TCS TORQUE REQUEST CIRCUIT (4.6L "E" & "K" BODIES)

DTC P1571: ASR DESIRED TORQUE CIRCUIT (5.7L "Y" BODY)

DTC P1573: EBTCM/PCM SERIAL DATA CIRCUIT (3.4L "N" BODY)

DTC P1573: EBTCM/PCM SERIAL DATA CIRCUIT (3.4L "U" SERIES)

DTC P1573: EBTCM/PCM SERIAL DATA CIRCUIT (3.8L "G" BODY)

DTC P1574: STOPLIGHT SWITCH CONTROL CIRCUIT (3.8L "F" BODY)

DTC P1574: STOPLIGHT SWITCH CIRCUIT (4.0L "G" BODY & 4.6L "E" & "K" BODIES)

DTC P1574: STOPLIGHT SWITCH CONTROL CIRCUIT (5.7L "Y" BODY)

DTC P1575: EXTENDED TRAVEL BRAKE SWITCH CIRCUIT HIGH (4.0L "G" BODY)

DTC P1575: EXTENDED TRAVEL BRAKE SWITCH CIRCUIT (4.6L "E" & "K" BODIES)

DTC P1575: EXTENDED TRAVEL BRAKE SWITCH CIRCUIT HIGH (5.7L "Y" BODY)

DTC P1579: PARK/NEUTRAL-TO-DRIVE/REVERSE THROTTLE ANGLE-POWER REDUCTION MODE ACTIVE (4.0L "G" BODY & 4.6L "E" & "K" BODIES)

DTC P1580: CRUISE CONTROL MOVE CIRCUIT VOLTAGE LOW (1.9L SATURN)

DTC P1581: CRUISE CONTROL MOVE CIRCUIT VOLTAGE HIGH (1.9L SATURN)

DTC P1582: CRUISE CONTROL DIRECTION CIRCUIT LOW VOLTAGE (1.9L SATURN)

DTC P1583: CRUISE CONTROL DIRECTION CIRCUIT HIGH VOLTAGE (1.9L SATURN)

DTC P1584: CRUISE DISENGAGE (1.9L SATURN)

DTC P1585: CRUISE INHIBIT CONTROL CIRCUIT (3.4L "U" SERIES)

DTC P1585: CRUISE INHIBIT CONTROL CIRCUIT (3.5L "W" BODY)

DTC P1599: ENGINE STALL OR NEAR STALL DETECTED (4.0L "G" BODY & 4.6L "E" & "K" BODIES)

DTC P1602: ABS MESSAGE FAULT (1.9L SATURN)

DTC P1602: EBCM/EBTCM SERIAL DATA CIRCUIT (3.1L "N" & "W" BODIES)

DTC P1602: EBCM/EBTCM SERIAL DATA CIRCUIT (3.4L "N" BODY)

DTC P1602: LOSS OF EBTCM SERIAL DATA (3.5L "W" BODY)

DTC P1602: EBCM/EBTCM SERIAL DATA CIRCUIT (3.8L "C" & "W" BODIES)

DTC P1602: LOSS OF EBTCM SERIAL DATA (4.0L "G" BODY & 4.6L "E" & "K" BODIES)

DTC P1603: LOSS OF SDM SERIAL DATA (4.6L "E" & "K" BODIES)

DTC P1604: LOSS OF INSTRUMENT PANEL CLUSTER (IPC) SERIAL DATA (3.8L "C" BODY)

DTC P1604: LOSS OF INSTRUMENT PANEL CLUSTER (IPC) SERIAL DATA (4.0L "G" BODY & 4.6L "E" & "K" BODIES)

DTC P1605: HVAC SERIAL DATA CIRCUIT (3.1L "W" BODY - CENTURY ONLY)

DTC P1605: LOSS OF HVAC SERIAL DATA (3.5L "W" BODY)

DTC P1605: HVAC SERIAL DATA CIRCUIT (3.8L "W" BODY)

DTC P1605: LOSS OF HVAC SERIAL DATA (4.0L "G" BODY & 4.6L "E" & "K" BODIES)

DTC P1610: STANDARD BODY MODULE SERIAL DATA CIRCUIT (3.1L "N" & "W" BODIES)

DTC P1610: CLASS II FAILURE WITH BFC (3.4L "N" BODY)

DTC P1610: LOSS OF BCM SERIAL DATA (3.5L "W" BODY)

DTC P1610: STANDARD BODY MODULE SERIAL DATA CIRCUIT (3.8L "C" & "W" BODIES)

DTC P1610: LOSS OF PZM SERIAL DATA (4.6L "E" & "K" BODIES)

DTC P1611: LOSS OF CVRTD SERIAL DATA (4.6L "E" & "K" BODIES)

DTC P1612: LOSS OF IPM SERIAL DATA (4.6L "K" BODY - SEVILLE)

DTC P1613: LOSS OF DIM SERIAL DATA (4.6L "K" BODY - SEVILLE)

DTC P1614: LOSS OF RIM SERIAL DATA (4.6L "K" BODY - SEVILLE)

DTC P1615: LOSS OF VTD SERIAL DATA (4.6L "K" BODY - SEVILLE)

DTC P1619: ENGINE OIL LIFE MONITOR RESET CIRCUIT (3.8L "H" BODY)

DTC P1620: LOW COOLANT LEVEL CIRCUIT (1.9L SATURN)

DTC P1621: VCM EEPROM PERFORMANCE (4.3L "C", "K", "L", "M", "S" & "T" SERIES)

DTC P1621: VCM EEPROM PERFORMANCE (4.3L, 5.0L, 5.7L & 7.4L "C", "G", "K" & "P" SERIES)

DTC P1626: LOSS OF SERIAL COMMUNICATION WITH VEHICLE THEFT DETERRENT OR THEFT DETERRENT SYSTEM FUEL ENABLE CIRCUIT (2.2L "S" SERIES & 2.4L "J" & "N" BODIES)