Engine Controls - Tests W/codes Geo Storm I

INTRODUCTION

If no faults were found while performing BASIC TESTING , proceed with self-diagnostics. If no fault codes or only pass codes are present, proceed to TESTS W/O CODES article in the ENGINE PERFORMANCE Section for diagnosis by symptom (i.e., ROUGH IDLE, NO START, etc.).

CHECK ENGINE LIGHT

All models are equipped with a CHECK ENGINE light, located on the instrument panel. Light comes on, as a bulb check, when ignition switch is turned to the ON position and engine is not running. Light should not flash at this time, and should go out when engine is started.

If CHECK ENGINE light remains on, or flashes, with engine running, the self-diagnostic system has detected a problem. If the problem goes away, light will go out after 10 seconds, but a fault code will be stored in ECM memory.

Hard Failures

Hard failures will cause CHECK ENGINE light to illuminate and remain on until the malfunction is repaired. If light comes on and remains on (light may flash) during vehicle operation, cause of malfunction must be determined using diagnostic (code) charts. If a sensor fails, control unit will use a substitute value in its calculations to continue engine operation. In this condition, vehicle is functional, but loss of good driveability will most likely occur.

Intermittent Failures

Intermittent failures may cause CHECK ENGINE light to flicker or illuminate, and go out after the intermittent fault goes away. However, the corresponding fault code will be retained in control unit memory. If fault does not reoccur within a certain time frame, related fault code will be erased from control unit memory. Intermittent failures may be caused by sensor, connector or wiring related problems. See INTERMITTENTS in TESTS W/O CODES article in the ENGINE PERFORMANCE Section.

RETRIEVING CODES

1. Ensure ignition switch is in the OFF position. Using a jumper wire, connect ground and diagnostic terminals of Assembly Line Diagnostic Link (ALDL) White connector. (Scheme 9) Connector is located behind right kick panel in passenger compartment. Turn ignition switch to ON position. Read fault code(s). Proceed to appropriate charts under DIAGNOSTIC CODE CHARTS to diagnose fault codes. WARNING: Ensure jumper wire is connected to ALDL White connector. A connector for Supplemental Inflatable Restraint (SIR) system is located next to ALDL connector.
2. If no fault codes are stored, CHECK ENGINE light will flash on and off rapidly until jumper wire is disconnected. Count the number of flashes and look for pauses in flashing to ensure no fault codes are overlooked. If fault codes are stored, code will flash 3 times starting with the lowest code.

Scheme 9

FAULT CODE IDENTIFICATION (STORM)

Storm

Turn ignition switch to OFF position. Disconnect negative battery cable, or remove 30-amp main fuse in underhood fuse/relay block, for at least 30 seconds. ECM fault code memory is now clear. Connect negative battery cable.

ECM LOCATION

ECM is located behind left dash panel.

DIAGNOSTIC CIRCUIT CHECK

Diagnostic circuit check is the starting point for identifying a problem caused by the engine control system. ECM uses the CHECK ENGINE light to flash fault code(s). The lowest code number will be flashed first. If no codes were stored, see TESTS W/O CODES article in the ENGINE PERFORMANCE Section.

Scheme 10

CHART A-1, WON'T FLASH CODE 12/NO CHECK ENGINE LIGHT

There should always be a steady CHECK ENGINE light when the ignition is on and engine is off. Battery voltage is supplied directly to the light bulb. The Electronic Control Module (ECM) controls the light and turns it on by providing a ground path through the Purple wire.

Note. Test numbers refer to test numbers on diagnostic chart.

1. ECM battery feed terminals B1 and C16 are protected by a fusible link in fuse/relay block, near battery.
2. If ECM terminals B1 and C16 have voltage, then either ECM grounds or ECM is faulty.
3. Using a test light connected to 12 volts, probe each of the system ground circuits to ensure good ground is present.

DIAGNOSTIC AIDS

If engine runs okay, check the following

1. Light bulb.
2. Purple wire from light bulb to ECM for open.
3. METER fuse.

If fuse is blown, this may result in no Oil or Generator light, Seat Belt Reminder light, etc. If engine cranks, but will not run, check for the following conditions

1. Battery fuse or fusible link open.
2. ECM ignition fuse open.
3. Battery Red/White wire to ECM open.
4. Ignition Red/Green wire to ECM open.
5. Poor connection to ECM.

Scheme 11

Scheme 12

CHART A-2, NO ALDL DATA OR WON'T FLASH CODE 12/CHECK ENG LIGHT ON STEADY

There should always be a steady CHECK ENGINE light when the ignition is on, and engine is not running. Battery voltage is supplied directly to light bulb. ECM activates CHECK ENGINE light by grounding Purple wire at ECM.

With ALDL diagnostic connector grounded, CHECK ENGINE light should flash Code 12, followed by any fault code(s) stored in memory. A steady light indicates short to ground in the Purple wire, or an open in the Orange/Yellow wire.

Note. Test numbers refer to test numbers on diagnostic chart.

1. If a problem in ECM is causing Scan tester not to read serial data (ALDL connector terminal No. 2), then ECM should not flash Code 12. If Code 12 is flashed, ensure Scan tester is working properly on another vehicle. If Scan tester and Orange/Black wire are okay, ECM may be faulty.
2. If CHECK ENGINE light goes off when ECM connector is disconnected, then Purple wire is not shorted to ground.
3. This step checks for an open diagnostic Orange/Yellow wire.
4. CHECK ENGINE light wiring is okay. Problem is a faulty ECM. If Code 12 is not flashed, replace ECM.

Scheme 13

Scheme 14

CODE 13, O2 SENSOR CKT/OPEN CKT (VIN 5)

ECM supplies approximately .45 volt between ECM terminals D6 and D7. If voltage is measured with a 10-megohm DVOM, reading may be as low as .32 volt. The O2 sensor produces a varying voltage as engine reaches normal operating temperature. Voltage varies between .1-1.0 volt.

The O2 sensor will not produce voltage until sensor reaches 600°F (316°C). When sensor is less than this temperature, open loop condition exists.

Note. Test numbers refer to test numbers on diagnostic chart.

1. Code 13 sets if the following conditions are present for 60 seconds: Engine temperature is greater than 158°F (70°C). Engine has been running for at least 120 seconds after start. O2 signal voltage is steady between .347-.547 volt. Throttle angle is greater than 5 percent. If condition for Code 13 exist, system will not go into closed Loop.
2. This test determines if O2 sensor, ECM and/or wiring is faulty.
3. Use only high-impedance DVOM when performing this test. This checks continuity of terminals D6 and D7. If D6 is open, ECM voltage on D7 will be greater than .6 volt (600 mV).

Normal scan voltage varies between .1-1.0 volt (100-999 mV) while in closed Loop. Code 13 will set within one minute if voltage remains between .347-.547 volt, but system will go into open loop in about 15 seconds.

Verify ground connections are clean and tight at terminals D6 and D7. An open circuit in these terminals will result in Code 13. If code is intermittent, see TESTS W/O CODES article in the ENGINE PERFORMANCE Section.

Scheme 15

Scheme 16

CODE 13, O2 SENSOR CKT/OPEN CKT (VIN 6)

ECM supplies approximately .45 volt between ECM terminals D7 and D6. If voltage is measured with a 10-megohm DVOM, reading may be as low as .32 volt. The O2 sensor produces a varying voltage as engine reaches normal operating temperature. Voltage varies between .1-1.0 volt.

The O2 sensor will not produce voltage until sensor reaches 600°F (316°C). When sensor is less than this temperature, open loop condition exists.

Note. Test numbers refer to test numbers on diagnostic chart.

1. Code 13 sets if the following conditions are present for 60 seconds: Engine temperature is greater than 158°F (70°C). Engine has been running for at least 50 seconds after start. O2 signal voltage is steady between .347-.547 volt. Throttle angle is greater than 5 percent. If condition for Code 13 exist, system will not go into closed Loop.
2. This test determines Whether O2 sensor, ECM and/or wiring is faulty.
3. Use only high-impedance DVOM when performing this test. This checks continuity of terminals D6 and D7. If D6 is open, ECM voltage on D7 will be greater than .6 volt (600 mV).

Normal scan voltage varies between .1-1.0 volt (100-999 mV) while in closed loop. Code 13 will set within one minute if voltage remains between .347-.547 volt, but system will go into open loop in about 15 seconds.

Verify ground connections are clean and tight at terminals D6 and D7. An open circuit in these terminals will result in Code 13. If code is intermittent, see TESTS W/O CODES article in the ENGINE PERFORMANCE Section.

Scheme 17

Scheme 18

CODE 14, COOLANT TEMP SENSOR CKT/HIGH TEMP INDICATED

The coolant temperature sensor uses a thermistor to control signal voltage to ECM. ECM applies voltage on Gray/Black wire to the sensor. When engine is cold, thermistor resistance is high. Thus, ECM will sense high signal voltage.

As engine warms, thermistor resistance decreases, and ECM senses low signal voltage. When engine reaches normal operating temperature, signal voltage will be approximately 1.5-2.0 volts at ECM terminal C10. Coolant temperature is one of the inputs used by ECM to control fuel delivery, Electronic Spark Control (EST), and Idle Air Control (IAC).

Note. Test numbers refer to test numbers on diagnostic chart.

1. This checks if code is due to a hard failure or an intermittent condition. Code 14 is set if signal voltage indicates coolant temperature is more than 275°F (135°C) for 3 seconds.
2. This simulates conditions for Code 14 (low temperature indicated). If ECM senses open circuit (high voltage) and displays low coolant temperature, ECM and wiring are okay.

After engine is started, engine coolant temperature should rise to approximately 194°F (90°C) and stabilize when thermostat opens. Code 14 is set if Gray/Black wire is shorted to ground. If code is intermittent, see TESTS W/O CODES article in the ENGINE PERFORMANCE Section.

COOLANT TEMPERATURE SENSOR RESISTANCE

Scheme 19

Scheme 20

CODE 14, COOLANT TEMP SENSOR CKT/LOW TEMP INDICATED

The coolant temperature sensor uses a thermistor to control signal voltage to ECM. ECM applies voltage on Gray/Black wire to the sensor. When engine is cold, thermistor resistance is high. ECM will sense high signal voltage.

As engine warms, thermistor resistance decreases, and ECM senses low signal voltage. When engine reaches normal operating temperature, signal voltage will be approximately 1.5-2.0 volts at ECM terminal C10. Coolant temperature is one of the inputs used by ECM to control fuel delivery, Engine Spark Timing (EST), and Idle Air Control (IAC).

Note. Test numbers refer to test numbers on diagnostic chart.

1. Checks if code is due to a hard failure or an intermittent condition. Code 14 is set if signal voltage indicates coolant temperature is less than -22°F (-30°C) after engine has been running for 2 minutes.
2. This simulates conditions for Code 14 (high temperature indicated). If ECM senses grounded circuit (low voltage) and displays high coolant temperature, ECM and wiring are okay.
3. This determines if ECM and/or wiring is faulty.

After engine is started, engine coolant temperature should rise to approximately 194°F (90°C) and stabilize when thermostat opens. If engine is allowed to cool to ambient temperature, or overnight, coolant and IAT sensor resistance or temperature may be checked with a Scan tester. Readings for both components should be the same, or close.

Code 14 is set if Gray/Black wire is open. If code is intermittent, see TESTS W/O CODES article in the ENGINE PERFORMANCE Section.

COOLANT TEMPERATURE SENSOR RESISTANCE

Scheme 21

CODE 21, THROTTLE POS SENSOR CKT/SIGNAL VOLTAGE HIGH

The Throttle Position Sensor (TPS) provides a voltage signal that changes relative to throttle opening. Signal voltage varies from less than 1.25 volts at idle to approximately 5 volts at Wide Open Throttle (WOT). TPS signal is one of the most important inputs used by the ECM for fuel control, and most ECM-controlled outputs.

Note. Test numbers refer to test numbers on diagnostic chart.

1. This checks if Code 21 is due to a hard failure or an intermittent condition. Code 21 is set if the following conditions are present for 2 seconds: TPS reading is greater than 2.5 volts, and engine speed is less than 1800 RPM with a low MAP reading.
2. Simulates conditions for Code 21 (signal voltage low). If the ECM recognizes a change, ECM, Yellow/Blue wire and Blue/Orange wire are okay.
3. This isolates a faulty sensor or ECM, or an open in Black/White wire. If Black/White wire is open, Code 23 may also be present.

With throttle closed, TPS voltage should be less than 1.25 volt. TPS voltage should steadily increase as throttle is opened. Code 21 will appear if Yellow/Blue wire is shorted to voltage, or ground wire is open. If code is intermittent, see TESTS W/O CODES article in the ENGINE PERFORMANCE Section.

Scheme 22

Scheme 23

CODE 21, THROTTLE POS SENSOR CKT/SIGNAL VOLTAGE LOW

The Throttle Position Sensor (TPS) provides a voltage signal that changes relative to throttle opening. Signal voltage varies from less than 1.25 volts at idle to approximately 5.0 volts at wide open throttle. TPS signal is one of the most important inputs used by the ECM for fuel control, and most ECM-controlled outputs.

Note. Test numbers refer to test numbers on diagnostic chart.

1. This checks if Code 21B is due to a hard failure or an intermittent condition. Code 21B is set if engine is running and TPS reading is less than .2 volt (200 mV).
2. Simulates conditions for Code 21 (signal voltage high). If Code 21 (signal voltage high) is set, or Scan tester displays more than 4 volts, ECM and wiring are okay.
3. Isolates cause of problem. If Scan tester displays more than 4 volts, Yellow/Blue wire and ECM are okay.
4. If Purple/Orange wire is open or shorted to ground, Code 33 may also be stored.

With throttle closed, TPS voltage should be less than 1.25 volts. TPS voltage should steadily increase as throttle is opened. Code 21 will appear if Blue/Orange or Yellow/Blue wire is open or shorted. If code is intermittent, see TESTS W/O CODES article in the ENGINE PERFORMANCE Section.

Scheme 24

CODE 23, INTAKE AIR TEMP SENSOR CKT LOW TEMP INDICATED

The IAT sensor uses a thermistor to control signal voltage to ECM. ECM applies 4-6 volts on Blue/Black wire to sensor. When intake manifold air is cold, the sensor (thermistor) resistance is high and the ECM senses a high voltage. As the intake air warms, the sensor resistance becomes less, and voltage drops.

Note. Test numbers refer to test numbers on diagnostic chart.

1. This checks if Code 23 is due to a hard failure or an intermittent condition. Code 23 is set if engine has been running longer than 2 minutes and signal voltage indicates IAT temperature is less than -22°F (-30°C).
2. Simulates conditions for a Code 23 (high temperature indicated). If Scan tester displays a high temperature, ECM and wiring are okay.
3. Checks continuity of Blue/Black and Black wires. If Black wire is open, a Code 21 may also be present.

When engine is allowed to cool to ambient temperature, or overnight, CTS and IAT sensor resistance or temperature may be checked with a Scan tester. Readings of components should be close to each other.

Code 23 is set if Blue/Black wire or Black wire is open. If code is intermittent, see TESTS W/O CODES article in the ENGINE PERFORMANCE Section.

IAT SENSOR RESISTANCE

Scheme 25

Scheme 26

CODE 23, INTAKE AIR TEMP CKT/HIGH TEMP INDICATED

The IAT sensor uses a thermistor to control signal voltage to ECM. ECM applies 4-6 volts on Blue/Black wire to sensor. When intake manifold air is cold, the sensor (thermistor) resistance is high, and ECM senses high voltage. As intake air warms, sensor resistance decreases, and the voltage drops.

Note. Test number refers to test numbers on diagnostic chart.

1. This checks if Code 23 is due to a hard failure or an intermittent condition. Code 23 is set if IAT temperature is greater than 293°F (145°C) for more than 2 seconds.

When engine is allowed to cool to ambient temperature, or overnight, CTS and IAT sensor resistance or temperature may be checked with a Scan tester. Readings of components should be close to each other.

Code 23 is set if Blue/Black wire is shorted to ground. If code is intermittent, see TESTS W/O CODES article in the ENGINE PERFORMANCE Section.

IAT SENSOR RESISTANCE

Scheme 27

CODE 24, VEHICLE SPEED SENSOR CIRCUIT

The Vehicle Speed Sensor (VSS) is a reed switch located behind instrument panel. The ECM provides battery voltage to switch, which toggles the voltage high and low. This pulsed signal is used by ECM to determine vehicle speed (MPH or km/h).

Note. Test numbers refer to test numbers on diagnostic chart.

1. Code 24 is set if vehicle speed equals 0 MPH under the following conditions: Engine speed is between 1500-4400 RPM. VSS indicates less than 3 MPH. No Code 33 stored in memory. MAP reads low voltage with high vacuum (low load condition). Gear is not in Park or Neutral. All conditions are met for 5 seconds. These conditions are met during a road-load deceleration. Disregard Code 24 that is set when drive wheels are not turning.

Scan tester should indicate a vehicle speed whenever the drive wheels are turning faster than 3 MPH.

Check White wire (A10) for proper connection. Ensure wire connector is clean and tight, and harness is routed correctly. On automatic transmission, a faulty or misadjusted Park/Neutral switch can result in a false Code 24. Use a Scan tester and check for proper signal while in Drive. To check P/N switch, refer to I - SYS/COMP TESTS article in the ENGINE PERFORMANCE Section. If code is intermittent, see TESTS W/O CODES article in the ENGINE PERFORMANCE Section.

Scheme 28

Scheme 29

CODE 32, EGR SYSTEM ERROR (CALIF. ONLY)

A driver inside the ECM provides ground for EGR Vacuum Switching Valve (VSV). By turning the VSV on and off, ECM controls vacuum source to EGR modulator. EGR modulator regulates vacuum to EGR valve using exhaust back pressure.

The EGR gas temperature sensor, mounted in base of EGR valve, is used by the ECM to ensure EGR functions properly. The EGR gas temperature sensor contains a thermistor. ECM provides a 5-volt reference signal and a ground circuit for the EGR gas temperature sensor. ECM monitors EGR gas temperature sensor to determine if EGR valve functions when EGR is commanded upon. If EGR valve fails to open, EGR gas temperature sensor will signal low temperature to ECM. If EGR valve is stuck open, the EGR gas temperature sensor will indicate high temperature. Code 32 will be stored and the CHECK ENGINE light will illuminate.

Code 32 will set when one of the following conditions is present for 120 seconds

1. High EGR temperature indicated at idle.
2. Low EGR temperature indicated when EGR is commanded upon.
3. Open or short in EGR gas temperature sensor circuit.

EGR is not enabled if coolant temperature is less than 69°F (21°C).

Note. Test numbers refer to test numbers on diagnostic chart.

1. Checks for EGR gas temperature sensor 5-volt reference signal.
2. Checks for a poor ground or an open ground wire.
3. Checks for a short to voltage in EGR gas temperature sensor 5-volt reference signal.
4. Checks EGR gas temperature sensor resistance.
5. A non-functioning EGR valve will cause Code 32 to set.

A faulty connection or "shifted" EGR gas temperature sensor could cause Code 32 to set. To check for a "shifted" EGR gas temperature sensor, connect a DVOM to Gray/Black and Black wires. Start engine and check resistance of EGR gas temperature sensor against values in EGR TEMPERATURE SENSOR RESISTANCE table. If code is intermittent, see TESTS W/O CODES article in the ENGINE PERFORMANCE Section.

EGR TEMPERATURE SENSOR RESISTANCE

Scheme 30

Scheme 31

CODE 33, MAP SENSOR CKT/SIGNAL VOLTAGE HIGH-LOW VACUUM

The MAP sensor responds to changes in manifold pressure (vacuum). ECM receives a signal voltage varying between 1-1.5 volts at idle (closed throttle) to 4-4.5 volts at Wide Open Throttle (WOT). If the MAP sensor fails, ECM substitutes a fixed MAP value and uses TPS input to control fuel delivery.

Note. Test numbers refer to test numbers on diagnostic chart.

1. This determines if Code 33 is due to a hard failure or an intermittent condition. Code 33 is set if the following conditions are present for 5 seconds or longer: MAP signal indicates low vacuum. No Code 21 is set. TPS is less than 5 percent.
2. Simulates conditions for Code 33 (signal voltage low high vacuum). If ECM recognizes the change, ECM, Gray wire, and Blue/Orange wire are okay. If Gray/Red wire is open, Code 23 may also be stored.

With ignition on and engine off, manifold pressure is equal to atmospheric pressure, and signal voltage will be high. This information is used by ECM as an indication of vehicle altitude, and is referred to as BARO. Comparison of this BARO reading with a known good vehicle with the same sensor is a good way to check accuracy of suspected sensor. Readings should be +/- .4 volt.

Code 33 is set if Gray wire is open, or if Gray/Red wire is shorted to voltage or shorted to Blue/Orange wire. If code is intermittent, see TESTS W/O CODES article in the ENGINE PERFORMANCE Section.

Scheme 32

Scheme 33

CODE 33, MAP SENSOR CKT/SIGNAL VOLTAGE LOW-HIGH VACUUM

The MAP sensor responds to changes in manifold pressure (vacuum). ECM receives a signal voltage varying between 1-1.5 volts at idle (closed throttle) to 4-4.5 volts at Wide Open Throttle (WOT). If MAP sensor fails, ECM substitutes a fixed MAP value and uses TPS input to control fuel delivery.

Note. Test numbers refer to test numbers on diagnostic chart.

1. This determines if Code 33B is due to a hard failure or an intermittent condition. Code 33 will set under the following conditions: Engine RPM is greater than 1200 RPM. No Code 21 is set. TPS is greater than 15 percent. MAP signal voltage is too low.
2. Jump harness terminal "B" to terminal "C" determines whether sensor is faulty, or problem is in the ECM or wiring.
3. Isolates cause of problem. If Scan tester indicates more than 4 volts, ECM and Gray/Red wire are okay.

With ignition on and engine off, manifold pressure is equal to atmospheric pressure, and signal voltage will be high. This information is used by ECM as an indication of vehicle altitude, and is referred to as BARO. Comparison of this BARO reading with a known good vehicle with same sensor is a good way to check accuracy of suspected sensor. Readings should be +/- .4 volt.

Code 33 is set if Blue/Orange or Gray/Red wire is open or shorted to ground. If code is intermittent, see TESTS W/O CODES article in the ENGINE PERFORMANCE Section.

Scheme 34

CODE 42, ELECTRONIC SPARK TIMING

When engine speed is less than 400 RPM, the ignition module controls ignition timing. When engine speed is greater than 400 RPM, ECM applies 5 volts to the by-pass line, switching ignition timing control over to ECM.

When system is running on the ignition module (no voltage on by-pass line), the ignition module grounds the Electronic Spark Timing (EST) signal. The ECM expects to see no voltage on the EST line during this condition. If the ECM sees a voltage signal, it sets Code 42 and will not go into EST mode.

When RPM for EST is reached (about 400 RPM), and voltage is applied on the by-pass line, EST should no longer be grounded in the ignition module, thus EST voltage should be varying. If the by-pass line is open or grounded, the ignition module will not switch to EST. The EST voltage would be low, setting Code 42.

Note. Test numbers refer to test numbers on diagnostic chart.

1. Code 42 indicates ECM has detected an open or short to ground in the EST or by-pass circuit. This confirms that Code 42 and fault causing the code exist.
2. Checks for normal EST ground path through the ignition module. An EST Yellow wire shorted to ground will also read less than 500 ohms.
3. As the test light voltage touches Yellow/Green wire, the module should switch, causing an overrange if ohmmeter is in the 1000-2000 ohm scale. Setting ohmmeter in the 10,000-20,000 ohms scale will give a reading more than 5000 ohms. Ensure module switches.
4. If module does not switch, check for shorted EST Yellow wire, open by-pass Yellow/Green wire, faulty ignition module connection or faulty module.
5. This confirms Code 42 is caused by a faulty ECM, not an intermittent problem in Yellow or Yellow/Green wire.

Scheme 35

Scheme 36

CODE 44, O2 SENSOR CKT/LEAN EXHAUST INDICATED

ECM supplies a voltage of approximately .43 volt between ECM terminals D6 and D7. If voltage is measured with a 10-megohm DVOM, reading may be as low as .32 volt. The O2 sensor varies voltage within range of .1 volt (lean exhaust) to 1 volt (rich exhaust). When sensor temperature is less than 600°F (316°C), the sensor acts like an open circuit and will not produce voltage. A cold sensor, or open sensor circuit, causes open Loop condition.

Note. Test number refers to test numbers on diagnostic chart.

1. Code 44 is set when O2 sensor signal voltage is fixed above .280 mV, TPS is more than 3 percent, Codes 21 and 33 are not present, system is in closed loop, coolant temperature is less than 155°F (68°C), and integrator count is not at 128.

Using a Scan tester, observe block learn value at different RPM. Scan tester also displays the block cells, so the block learn values in each cell can be checked to determine when Code 44 may have been set. If the conditions for Code 44 exist, the block learn values will be about 150.

Ensure O2 sensor pigtail is not contacting exhaust manifold. Check for ground in wire between connector and sensor. Check for fuel contamination. Water causes a lean exhaust and can set Code 44. Check fuel pressure. System will be lean if fuel pressure is low. Check for exhaust leaks. If there is an exhaust leak, engine pulls outside air into the exhaust past the O2 sensor. Vacuum or crankcase leaks can also cause a lean condition.

If the wrong fuel injectors are installed in vehicle, this will also cause a lean condition. If code is intermittent, see TESTS W/O CODES article in the ENGINE PERFORMANCE Section.

Scheme 37

CODE 45, O2 SENSOR CKT/RICH EXHAUST INDICATED

ECM supplies a voltage of approximately .43 volt between ECM terminals D6 and D7. If voltage is measured with a 10-megohm DVOM, reading may be as low as .32 volt. The O2 sensor varies the voltage within a range of .1 volt (lean exhaust) to 1 volt (rich exhaust). When sensor temperature is less than 600°F (316°C), the sensor acts like an open circuit and will not produce voltage. A cold sensor, or open sensor circuit, causes open loop condition.

Note. Test numbers refer to test numbers on diagnostic chart.

1. Code 45 is set when O2 sensor signal voltage is fixed above .75 volt (750 mV), TPS is more than 3 percent, Codes 21 and 33 are not present, system is in closed Loop, coolant temperature is less than 155°F (68°C), and integrator count is not at 128.

Code 45 or rich exhaust is most likely caused by improper fuel pressure, HEI shielding, canister purge, MAP sensor, TPS, O2 sensor contamination, or EGR system. If code is intermittent, see TESTS W/O CODES article in the ENGINE PERFORMANCE Section. On VIN 5, if O2 sensor heater fails, Code 44 or Code 45 may set. To diagnose heater part of O2 sensor, refer to I - SYS/COMP TESTS article in the ENGINE PERFORMANCE Section.

Scheme 38

CODE 51, ECM FAILURE/ECM FAILED OR PROM FAILURE

Ensure all ECM connections are good. If connections are okay, clear memory and recheck ECM. If Code 51 reappears, replace ECM and reprogram.

SUMMARY

If no hard fault codes (or only pass codes) are present, proceed to TESTS W/O CODES article in the ENGINE PERFORMANCE Section for diagnosis by symptom (i.e., ROUGH IDLE, NO START, etc.) or intermittent diagnostic procedures.