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Engine Controls - Self-Diagnostics - 2.4: Diagnosis Nissan Altima L30 рестайлинг

Testing & Diagnostics 1 illustration ~8042 words

DTC Confirmation Test "A"

Malfunction is detected when ECM receives an excessively high voltage from MAF sensor when engine is not running. Possible causes are

  1. MAF sensor circuit open or shorted.
  2. Defective MAF sensor.

Depending on equipment available, use one of the following to set DTC

  1. Using Scan Tool Turn ignition on. Wait 6 seconds, then select MODE 7.
  2. Using MIL Turn ignition on. Wait 6 seconds and turn ignition off. Wait at least 5 seconds and turn ignition on. Retrieve DTCs using MIL. See SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS - INTRODUCTION article.

DTC Confirmation Test "B"

Malfunction is detected when ECM receives an excessively low voltage from MAF sensor when engine is running. ECM will enter fail-safe mode. Possible causes are

  1. MAF sensor circuit open or shorted.
  2. Intake air leaks.
  3. Defective MAF sensor.

Depending on equipment available, use one of the following to set DTC

  1. Using Scan Tool Start engine and wait no more than 5 seconds. Select MODE 7.
  2. Using MIL Start engine and wait no more than 5 seconds. Turn ignition off and wait at least 5 seconds. Turn ignition on and retrieve DTCs using MIL. See SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS - INTRODUCTION article.

DTC Confirmation Test "C"

Malfunction is detected when ECM receives an excessively high voltage from MAF sensor under light-load driving conditions. Possible causes are

  1. MAF sensor circuit open or shorted.
  2. Defective MAF sensor.

Depending on equipment available, use one of the following to set DTC

  1. Using Scan Tool Start engine and warm to normal operating temperature. Run engine for at least 10 seconds at idle speed and select MODE 7.
  2. Using MIL Start engine and warm to normal operating temperature. Run engine for at least 10 seconds and turn ignition off. Wait at least 5 seconds and turn ignition on. Retrieve DTCs using MIL. See SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS - INTRODUCTION article.

DTC Confirmation Test "D" (Overall Function Check)

Note. Use the following procedure to check overall function of MAF sensor circuit. During this test, DTC may not be confirmed.

Malfunction is detected when ECM receives an excessively low voltage from MAF sensor voltage under heavy-load driving conditions. Possible causes are

  1. MAF sensor circuit open or shorted.
  2. Intake air leaks.
  3. Defective MAF sensor.

Depending on equipment available, use one of the following to set DTC

  1. Using Scan Tool Start engine and warm to normal operating temperature. Select MODE 1 and monitor mass airflow. Increase engine speed to 4000 RPM. Mass airflow output should increase as engine speed increases.
  2. Using MIL Start engine and warm to normal operating temperature. Measure voltage between ground and ECM terminal No. 47 by backprobing. see scheme 2 While monitoring voltage, increase engine speed to 4000 RPM. Voltage should increase as engine speed increases.

DTC Confirmation Test

Malfunction is detected when ECM receives an excessively low or high voltage from AP sensor. Possible causes are

  1. AP sensor circuit open or shorted.
  2. Defective AP sensor.

Depending on equipment available, use one of the following to set DTC

  1. Using Scan Tool Turn ignition on. Wait at least 6 seconds then select MODE 7.
  2. Using MIL Turn ignition on. Wait at least 6 seconds and turn ignition off. Wait at least 5 seconds and turn ignition on. Retrieve DTCs using MIL. See SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS - INTRODUCTION article.

Malfunction "A" is detected when ECM receives an excessively low or high voltage from IAT sensor. Possible causes are

  1. IAT sensor circuit open or shorted.
  2. Defective IAT sensor.

Depending on equipment available, use one of the following to set DTC

  1. Using Scan Tool Turn ignition on. Wait 5 seconds then select MODE 7.
  2. Using MIL Turn ignition on. Wait 5 seconds and turn ignition off. Wait at least 5 seconds and turn ignition on. Retrieve DTCs using MIL. See SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS - INTRODUCTION article.

Malfunction "B" is detected when ECM receives an incorrect voltage from IAT sensor, compared to Engine Coolant Temperature (ECT) sensor voltage. Possible causes are

  1. IAT sensor circuit open or shorted.
  2. Defective IAT sensor.

Depending on equipment available, use one of the following to set DTC

  1. Using Scan Tool Turn ignition on and select MODE 1. Ensure engine coolant temperature is less than 194°F (90°C) for entire procedure. Start engine and drive vehicle at 44 MPH or more for 105 consecutive seconds. Select MODE 7.
  2. Using MIL Turn ignition on. Measure voltage between ECM terminal No. 51 and ground by backprobing. see scheme 2 Voltage should be more than one volt. If voltage is not more than one volt, allow engine to cool until voltage is more than one volt. Ensure voltage does not decrease to less than one volt for entire procedure. Start engine and operate vehicle at 44 MPH or more for 105 consecutive seconds. Turn ignition off and wait at least 5 seconds. Turn ignition on and retrieve DTCs using MIL. See SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS - INTRODUCTION article.

DTC Confirmation Test (DTC P0115)

Malfunction is detected when ECM receives an excessively low or high voltage from ECT sensor. ECM will enter fail-safe mode. Possible causes are

  1. ECT sensor circuit open or shorted.
  2. Defective ECT sensor.

Depending on equipment available, use one of the following set DTC

  1. Using Scan Tool Turn ignition on. Wait at least 5 seconds, then select MODE 7.
  2. Using MIL Turn ignition on. Wait at least 5 seconds and turn ignition off. Wait at least 5 seconds and turn ignition on. Retrieve DTCs using MIL. See SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS - INTRODUCTION article.

DTC Confirmation Test (DTC P0125)

Malfunction is detected when ECT sensor voltage is incorrect, based on engine run time (engine coolant temperature too low). Possible causes are

  1. High resistance in ECT sensor circuit.
  2. Defective ECT sensor.
  3. Stuck open thermostat.

Depending on equipment available, use one of the following to set DTC

  1. Using Scan Tool Turn ignition on. Select MODE 1. Ensure coolant temperature is less than 50°F (10°C). Start engine and let it idle for 65 minutes. Select MODE 7. DTC will set if coolant temperature does not increase to more than 50°F (10°C).
  2. Using MIL Turn ignition on. Measure voltage between ground and ECM terminal No. 51 by backprobing. see scheme 2 Ensure voltage is more than 3.8 volts. Start engine and let it idle for 65 minutes. Voltage should be less than 3.8 volts. Turn ignition off and wait at least 5 seconds. Turn ignition on and retrieve DTCs using MIL. See SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS - INTRODUCTION article. DTC will set if voltage does not decrease to less than 3.8 volts.

Malfunction "A" is detected when ECM receives an excessively low or high voltage from TP sensor voltage. ECM will enter fail-safe mode. Possible causes are

  1. TP sensor circuit open or shorted.
  2. Defective TP sensor.

Depending on equipment available, use one of the following to set DTC

  1. Using Scan Tool Start engine and drive vehicle for at least 5 seconds at 2 MPH or more. Ensure transmission is NOT in Neutral. Select MODE 7.
  2. Using MIL Start engine and drive vehicle for at least 5 seconds at 2 MPH or more. Ensure transmission is not in Neutral. Stop vehicle and turn ignition off. Wait at least 5 seconds and turn ignition on. Retrieve DTCs using MIL. See SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS - INTRODUCTION article.

Malfunction "B" is detected when ECM receives a high voltage from TP sensor under light-load driving conditions. Possible causes are

  1. TP sensor circuit open or shorted.
  2. Defective TP sensor.
  3. Defective fuel injector.
  4. Defective Camshaft Position (CMP) sensor.
  5. Defective Mass Airflow (MAF) sensor.

Depending on equipment available, use one of the following to set DTC

  1. Using Scan Tool Start engine and let it idle for at least 10 seconds. If idle speed is more than 1100 RPM, depress brake pedal and shift A/T into Drive, or M/T into 3rd or 4th gear. Select MODE 7.
  2. Using MIL Start engine and let it idle for at least 10 seconds. If idle speed is more than 1100 RPM, depress brake pedal and shift A/T into Drive, or M/T into 3rd or 4th gear. Turn ignition off and wait at least 5 seconds. Turn ignition on and retrieve DTCs using MIL. See SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS - INTRODUCTION article.

Malfunction "C" is detected when ECM receives a low voltage from TP sensor under heavy-load driving conditions. Possible causes are

  1. TP sensor circuit open or shorted.
  2. Intake air leaks.
  3. Defective TP sensor.

Depending on equipment available, use one of the following to set DTC

  1. Using Scan Tool Select MODE 1 and monitor engine speed, MAF sensor voltage and engine coolant temperature. Drive vehicle under a heavy-load condition (engine speed more than 2000 RPM and MAF sensor voltage more than 3 volts) with engine coolant temperature more than 158°F for at least 10 consecutive seconds. Select MODE 7.
  2. Using MIL Measure voltage between ECM terminal No. 51 (engine coolant temperature signal) and ground by backprobing. see scheme 2 Warm engine until voltage is less than 1.5 volts. Move voltmeter lead from ECM terminal No. 51 to terminal No. 47 (MAF sensor signal). Drive vehicle under a heavy-load condition with engine speed more than 2000 RPM and MAF sensor voltage more than 3 volts for at least 10 consecutive seconds. Stop vehicle and turn ignition off. Wait at least 5 seconds and turn ignition on. Retrieve DTCs using MIL. See SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS - INTRODUCTION article.

DTC Confirmation Test (Overall Function Check)

Note. Use the following test to check overall function of front HO2S circuit. During this test, DTC may not be confirmed.

Malfunction is detected when ECM receives a constant .3 volt from front HO2S. When ECM is not using front HO2S signal as an input, ECM circuits read a continuous .3 volt. Therefore, ECM monitors the time that front HO2S voltage is .2-.4 volt. DTC will set if time is too long. Possible causes are

  1. HO2S circuit open or shorted.
  2. Defective HO2S.

To check overall function of front HO2S circuit, start engine and warm to normal operating temperature. Measure voltage between ECM terminal No. 46 and engine ground by backprobing. see scheme 1and see scheme 2. While monitoring voltmeter, increase engine speed to 2000 RPM. Voltage should not remain in the.2-.4 volt range.

Note. Use the following test to check overall function of front HO2S circuit. During this test, DTC may not be confirmed.

Malfunction is detected when front HO2S "rich" output is not high enough or "lean" output is not low enough. DTC P0131 will set if both "rich" and "lean" outputs are shifted to the lean side. DTC P0132 will set if both "rich" and "lean" outputs are shifted to the rich side. Possible causes are

  1. Defective HO2S.
  2. Defective HO2S heater.
  3. Fuel pressure incorrect.
  4. Defective injectors.
  5. Intake air leaks.

To check overall function of front HO2S circuit, start engine and warm to normal operating temperature. Measure voltage between ECM terminal No. 46 and ground by backprobing. see scheme 1and see scheme 2. While monitoring voltmeter, increase engine speed to 2000 RPM. The following conditions should exist

  1. Maximum voltage should be more than .6 volt at least once.
  2. Minimum voltage should be more than .1 volt at least once
  3. Maximum voltage should be less than .8 volt at least once.
  4. Minimum voltage should be less than .35 volt at least once.

Note. Use the following test to check overall function of front HO2S circuit. During this test, DTC may not be confirmed.

Malfunction is detected when HO2S response time is too long. Possible causes are

  1. HO2S circuit open or shorted.
  2. Defective HO2S.
  3. Defective HO2S heater.
  4. Fuel pressure incorrect.
  5. Defective injectors.
  6. Intake air leaks.
  7. Exhaust leaks.
  8. Defective PCV valve.
  9. Defective Mass Airflow (MAF) sensor.

To check overall function of front HO2S circuit, start engine and warm to normal operating temperature. Measure voltage between ECM terminal No. 46 and engine ground by backprobing. see scheme 1and see scheme 2. While monitoring voltmeter, increase engine speed to 2000 RPM. With ECM in Diagnostic Test Mode II, MIL should flash more than 5 times within 10 seconds.

Malfunction is detected when HO2S voltage is too high. Possible causes are

  1. HO2S circuit open or shorted.
  2. Defective HO2S.

Depending on equipment available, use one of the following to set DTC

  1. Using Scan Tool Start engine and warm to normal operating temperature. Turn ignition off and wait at least 5 seconds. Start engine and let it idle for 35 seconds. Turn ignition off and wait at least 5 seconds. Start engine and let it idle for 35 seconds. Select MODE 3.
  2. Using MIL Start engine and warm to normal operating temperature. Turn ignition off and wait at least 5 seconds. Start engine and let it idle for 35 seconds. Turn ignition off and wait at least 5 seconds. Turn ignition on and retrieve DTCs using MIL. See SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS - INTRODUCTION article.

Malfunction is detected when front HO2S heater circuit current is out of normal range. Possible causes are

  1. HO2S heater circuit open or shorted.
  2. Defective HO2S heater.

Depending on equipment available, use one of the following to set DTC

  1. Using Scan Tool Start engine and let it idle for at least 5 seconds. Turn ignition off and wait at least 5 seconds. Start engine and let it idle for at least 5 seconds. Select MODE 3 with scan tool.
  2. Using MIL Start engine and let it idle for at least 5 seconds. Turn ignition off and wait at least 5 seconds. Turn ignition on and retrieve DTCs using MIL. See SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS - INTRODUCTION article.

Note. Use the following test to check overall function of rear HO2S circuit. During this test, DTC may not be confirmed.

DTC P0137 will set if rear HO2S minimum voltage is too high. DTC P0138 will set if rear HO2S maximum voltage is too low. DTC P0139 will set if rear HO2S response time is too long. DTC P0140 will set if rear HO2S voltage is too high. Possible causes are

  1. HO2S circuit open or shorted.
  2. Defective HO2S.
  3. Fuel pressure incorrect.
  4. Defective injectors.
  5. Intake air leaks.

To check overall function of rear HO2S circuit, drive vehicle at a speed of more than 43 MPH for 2 consecutive minutes. Stop vehicle and leave engine running. Measure voltage between ground and ECM terminal No. 52 by backprobing. see scheme 2 While monitoring voltmeter, quickly increase engine speed to 4000 RPM and release accelerator pedal. Repeat 10 times.

  1. Voltage should be less than .54 volt at least once.
  2. Voltage should be more than .56 volt at least once.
  3. Voltage should change at least .06 volt in one second.
  4. Voltage should be less than 2 volts during test.

If voltage is not as specified, allow engine to idle for 10 minutes and recheck voltage. If voltage is still not as specified, allow vehicle to coast at 50 MPH with overdrive off (A/T), or with transmission in 3rd gear (M/T), and recheck voltage.

Malfunction is detected when rear HO2S heater circuit current is out of normal range. Possible causes are

  1. HO2S heater circuit open or shorted.
  2. Defective HO2S heater.

Depending on equipment available, use one of the following to set DTC

  1. Using Scan Tool Drive vehicle at a speed of more than 43 MPH for 2 consecutive minutes. Turn ignition off and wait at least 5 seconds. Drive vehicle at a speed of more than 43 MPH for 2 consecutive minutes. Select MODE 3.
  2. Using MIL Drive vehicle at a speed of more than 43 MPH for 2 consecutive minutes. Turn ignition off and wait at least 5 seconds. Turn ignition on and retrieve DTCs using MIL. See SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS - INTRODUCTION article.

Malfunction is detected when mixture ratio compensation amount is too large (mixture is too lean or too rich). Possible causes are

  1. Intake air leaks.
  2. Defective front HO2S.
  3. Defective injectors.
  4. Exhaust leaks.
  5. Fuel pressure incorrect.
  6. Lack of fuel.
  7. Defective MAF sensor.

Depending on equipment available, use one of the following to set DTC

  1. Using Scan Tool Start engine and warm to normal operating temperature. Turn ignition off and wait at least 5 seconds. Disconnect MAF sensor harness connector located near air cleaner. Start engine and let it idle for at least 3 seconds. Turn ignition off and reconnect MAF sensor harness connector. Turn ignition on. Select MODE 7 and ensure that DTC P0100 is set. Select MODE 4 and erase DTCs. Start engine and let it idle for at least 10 minutes. Select MODE 7 and check for DTCs. If DTC P0171 or P0172 is present, go to «PROCEDURE»(ref-2731-S07003525662000041200000) . If engine was difficult to start, fuel injection system has a malfunction. Attempt to start engine while depressing accelerator pedal. If engine does not start, check for intake or exhaust leaks or spark plug fouling.
  2. Using MIL Start engine and warm to normal operating temperature. Turn ignition off and wait at least 5 seconds. Disconnect MAF sensor harness connector. Start engine and let it idle for at least 3 seconds. Turn ignition off and reconnect MAF sensor harness connector. Turn ignition on and retrieve DTCs using MIL. See SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS - INTRODUCTION article. Ensure DTC P0100 is set. Erase codes by switching ECM to Diagnostic Test Mode I. Start engine and let it idle for at least 10 minutes. Retrieve DTCs using MIL. If DTC P0171 or P0172 is present, go to «PROCEDURE»(ref-2731-S07003525662000041200000) . If engine was difficult to start, fuel injection system has a malfunction. Attempt to start engine while depressing accelerator pedal. If engine does not start, check for intake or exhaust leaks or spark plug fouling.

Malfunction is detected when ECM receives an excessively low or high voltage from FTT sensor, or when voltage received is rationally incorrect compared to ECT sensor and IAT sensor. Possible causes are

  1. FTT sensor circuit open or shorted.
  2. Defective FTT sensor.

Depending on equipment available, use one of the following to set DTC

  1. Using Scan Tool Turn ignition on. Wait at least 10 seconds then select MODE 7. If DTC is not set, select MODE 1 and monitor ECT sensor value. If engine coolant temperature is more than 140°F (60°C), turn ignition off and allow engine to cool to less than 140°F (60°C). Turn ignition on. Wait at least 10 seconds then select MODE 7.
  2. Using MIL Turn ignition on. Wait at least 10 seconds then turn ignition off. Wait at least 5 seconds then turn ignition on. Retrieve DTCs using MIL. See SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS - INTRODUCTION article. If DTC is not set, measure voltage between ground and ECM terminal No. 51 by backprobing. see scheme 2 If voltage is less than 1.9 volts, allow engine to cool until voltage is more than 1.9 volts. Turn ignition on and wait at least 10 seconds. Turn ignition off and wait at least 5 seconds. Turn ignition on and retrieve DTCs using MIL.

Misfire is detected when crankshaft position sensor detects a fluctuation in engine speed. Possible causes are

  1. Incorrect spark plugs.
  2. Insufficient compression.
  3. Incorrect fuel pressure.
  4. Defective EGR valve.
  5. Injector circuit open or shorted.
  6. Defective injectors.
  7. Intake air leak.
  8. Secondary ignition circuit open or shorted.
  9. Lack of fuel.
  10. Defective drive plate or flywheel.
  11. Defective front HO2S.
  12. Incorrect distributor rotor.

Depending on equipment available, use one of the following to set DTC

  1. Using Scan Tool Start engine and warm to normal operating temperature. Turn ignition off and wait at least 5 seconds. Start engine and drive vehicle at 1500-3000 RPM for at least 3 minutes. Hold accelerator pedal as steady as possible. Select MODE 7. If DTC did not set, refer to freeze frame data for driving conditions in which DTC was set.
  2. Using MIL Start engine and warm to normal operating temperature. Turn ignition off and wait at least 5 seconds. Start engine and drive vehicle at 1500-3000 RPM for at least 3 minutes. Hold accelerator pedal as steady as possible. Turn ignition off and wait at least 5 seconds. Turn ignition on and retrieve DTCs using MIL. See SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS - INTRODUCTION article.

Malfunction is detected when ECM receives an excessively low or high voltage from knock sensor. Possible causes are

  1. Knock sensor circuit open or shorted.
  2. Defective knock sensor.

Depending on equipment available, use one of the following to set DTC

  1. Using Scan Tool Start engine and let it idle for at least 5 seconds. Select MODE 3 on scan tool.
  2. Using MIL Start engine and let it idle for at least 5 seconds. Turn ignition off and wait at least 5 seconds. Turn ignition on and retrieve DTCs using MIL. See SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS - INTRODUCTION article.

DTC Confirmation Test (DTC P0335)

Malfunction is detected when ECM does not receive proper pulse signal from CKP sensor while engine is running at a certain speed. Possible causes are

  1. CKP sensor circuit open or shorted.
  2. Defective CKP sensor.
  3. Defective starter.
  4. Faulty starter circuit.
  5. Weak battery.

Depending on equipment available, use one of the following to set DTC

  1. Using Scan Tool Start engine and let it idle for at least 15 seconds. Select MODE 7.
  2. Using MIL Start engine and let it idle for at least 15 seconds. Turn ignition off and wait at least 5 seconds. Turn ignition on and retrieve DTCs using MIL. See SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS - INTRODUCTION article.

DTC Confirmation Test (DTC P1336)

Malfunction is detected when ECM detects chipping of flywheel or drive plate teeth. Possible causes are

  1. CKP sensor circuit open or shorted.
  2. Defective CKP sensor.
  3. Damaged flywheel or drive plate.

Depending on equipment available, use one of the following to set DTC

  1. Using Scan Tool Start engine and let it idle for at least 2 minutes. Select MODE 7.
  2. Using MIL Start engine and let it idle for at least 2 minutes. Turn ignition off and wait at least 5 seconds. Turn ignition on and retrieve DTCs using MIL. See SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS - INTRODUCTION article.

Malfunction is detected when either one-degree signal or 180-degree signal is not sent to ECM during engine cranking. Possible causes are

  1. CMP sensor circuit is open or shorted.
  2. Defective CMP sensor.
  3. Defective starter.
  4. Starter circuit fault.
  5. Weak battery.

Depending on equipment available, use one of the following to set DTC

  1. Using Scan Tool Crank engine for at least 2 seconds. Select MODE 7.
  2. Using MIL Crank engine for at least 2 seconds. Turn ignition off and wait 5 seconds. Turn ignition on and retrieve DTCs using MIL. See SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS - INTRODUCTION article.

DTC Confirmation Tests "B" & "C"

Malfunction "B" is detected when either one-degree signal or 180-degree signal is not sent to ECM often enough. Malfunction "C" is detected when the relationship between one-degree signal and 180-degree signal is out of normal range. Possible causes are

  1. CMP sensor circuit is open or shorted.
  2. Defective CMP sensor.
  3. Defective starter.
  4. Starter circuit fault.
  5. Weak battery.

Depending on equipment available, use one of the following to set DTC

  1. Using Scan Tool Start engine and let it idle for at least 2 seconds. Select MODE 7.
  2. Using MIL Start engine and let it idle for at least 2 seconds. Turn ignition off and wait 5 seconds. Turn ignition on and retrieve DTCs using MIL. See SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS - INTRODUCTION article.

Note. Use the following test to check overall EGR function. During this test, DTC may not be confirmed.

Malfunction is detected when EGR temperature sensor does not detect EGR flow under conditions that call for EGR. Possible causes are

  1. EGR valve stuck closed.
  2. Defective EGR Control Backpressure Transducer (EGRC-BPT).
  3. Vacuum hose leak or blockage.
  4. Defective EGR Control (EGRC) solenoid.
  5. EGR passage blocked.
  6. Defective EGR temperature sensor.
  7. Exhaust leak.

To check overall EGR function, start engine and warm to normal operating temperature. Raise drive wheels, and support vehicle. Shift transmission into a forward gear. Increase engine speed to 4000 RPM and check for EGR valve opening. EGR valve should open and close without sticking. If operation is not as specified, go to PROCEDURE . If operation is as specified, diagnose EGR temperature sensor or circuit failure. See DTC P1401: EGR TEMPERATURE SENSOR .

Note. Use the following test to check overall function of EGRC-BPT. During this test, DTC may not be confirmed.

Malfunction is detected when EGRC-BPT does not operate properly. Possible causes are

  1. Defective EGRC-BPT.
  2. Defective EGR valve.
  3. Backpressure hose blockage or leak.
  4. Defective Camshaft Position (CMP) sensor.
  5. Plugged exhaust.
  6. Missing orifice in hose between EGRC-BPT and EGRC solenoid.
  7. Defective Mass Airflow (MAF) sensor.
  8. Defective EGRC solenoid.

To check overall function of EGRC-BPT, Install vacuum gauge with a "T" to hose between EGRC-BPT and EGR valve. Raise drive wheels, and support vehicle. Start engine and shift transmission into 1st gear. Observe vacuum gauge while keeping engine speed at 2000-2800 RPM. Vacuum should be 0-5.91 in. Hg. If vacuum is not as specified, go to PROCEDURE . If vacuum is as specified, check EGR system vacuum hoses for blockages or leaks.

Note. Use the following test to check overall function of 3-way catalyst (warm-up 3-way catalyst on California models). During this test, DTC may not be confirmed.

Malfunction is detected when 3-way catalyst does not operate properly. Possible causes are

  1. Defective 3-way catalyst (warm-up 3-way catalyst on California models).
  2. Exhaust system damaged or leaking.
  3. Intake air leak.
  4. Defective injectors.
  5. Defective spark plug.
  6. Ignition timing incorrect.

To check overall function of 3-way catalyst, start engine and drive vehicle at 43 MPH or more for 2 minutes. Stop vehicle and leave engine running. Measure voltage between ground and ECM terminals No. 46 (front HO2S signal) and No. 52 (rear HO2S signal) by backprobing. see scheme 1and see scheme 2. Increase engine speed to 2000 RPM. Switching frequency of rear HO2S should be less than 75 percent of front HO2S switching frequency. If front HO2S does not switch more than 5 times within 10 seconds, diagnose front HO2S first. See DTC P0133: FRONT HEATED OXYGEN SENSOR (HO2S).

Malfunction is detected when improper voltage is sent to ECM through EVAP-CPVCV. Possible causes are

  1. EVAP-CPVCV circuit open or shorted.
  2. Defective EVAP-CPVCV.

Depending on equipment available, use one of the following to set DTC

  1. Using Scan Tool Start engine and let it idle for at least 13 seconds. Select MODE 7.
  2. Using MIL Start engine and let it idle for at least 13 seconds. Turn ignition off and wait at least 5 seconds. Turn ignition on and retrieve DTCs using MIL. See SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS - INTRODUCTION article.

Malfunction is detected when improper voltage is sent to ECM through EVAP-CVCV. Possible causes are

  1. EVAP-CVCV open or shorted.
  2. Defective EVAP-CVCV.

Depending on equipment available, use one of the following to set DTC

  1. Using Scan Tool Start engine and wait at least 8 seconds. Select MODE 7 on scan tool.
  2. Using MIL Start engine and wait at least 8 seconds. Turn ignition off and wait at least 5 seconds. Turn ignition on and retrieve DTCs using MIL. See SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS - INTRODUCTION article.

Malfunction is detected when improper voltage is sent to ECM from EVAP-CSPS. Possible causes are

  1. EVAP-CSPS circuit open or shorted.
  2. Blockage or leak in hose to EVAP-CSPS.
  3. Defective EVAP-CSPS.
  4. Defective EVAP Canister Vent Control Valve (EVAP-CVCV).
  5. Defective EVAP Canister Purge Volume Control Valve (EVAP-CPVCV).
  6. Defective EVAP canister.
  7. Faulty hose between EVAP-CVCV and water separator.

Depending on equipment available, use one of the following to set DTC

  1. Using Scan Tool Start engine and warm to normal operating temperature. Measure voltage between ground and ECM terminal No. 63 (fuel tank temperature sensor signal) by backprobing. see scheme 1and see scheme 2. Ensure voltage is less than 4.2 volts. Turn ignition off and wait at least 5 seconds. Start engine and wait at least 20 seconds. Select MODE 7 on scan tool.
  2. Using MIL Start engine and warm to normal operating temperature. Measure voltage between ground and ECM terminal No. 63 (fuel tank temperature sensor signal) by backprobing. see scheme 1and see scheme 2. Ensure voltage is less than 4.2 volts. Turn ignition off and wait at least 5 seconds. Start engine and wait at least 20 seconds. Turn ignition off and wait at least 5 seconds. Turn ignition on and retrieve DTCs using MIL. See SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS - INTRODUCTION article.

Malfunction is detected when EVAP system has a large leak or does not operate properly. Possible causes are

  1. Fuel filler cap open or leaking.
  2. Incorrect fuel tank vacuum relief valve.
  3. Incorrect fuel filler cap.
  4. Foreign matter in fuel filler cap.
  5. Leak in hose between intake manifold and EVAP Canister Purge Volume Control Valve (EVAP-CPVCV).
  6. Foreign matter in EVAP Canister Vent Control Valve (EVAP-CVCV).
  7. Leak in EVAP canister or fuel tank.
  8. Leak or blockage in EVAP purge line.
  9. Leak or blockage in hose to EVAP Control System Pressure Sensor (EVAP-CSPS).
  10. Defective EVAP-CVCV or circuit.
  11. Defective EVAP-CPVCV or circuit.
  12. Defective EVAP-CSPS.
  13. Defective fuel tank temperature sensor.
  14. Defective absolute pressure senor.
  15. Leak between EVAP canister and EVAP-CVCV.
  16. Defective refueling control valve.
  17. Leak in On Board Refueling Vapor Recovery (ORVR) system.
  1. Drive vehicle according to specified driving pattern to set System Readiness Test (SRT) codes. See SYSTEM READINESS TEST (SRT) CODES under ADDITIONAL SYSTEM FEATURES in SELF-DIAGNOSTICS - INTRODUCTION article. Stop vehicle and go to next step.
  2. Select MODE 1 on scan tool and check SRT status of EVAP system. If EVAP system SRT is complete, system is okay at this time. Problem may be intermittent. See TESTING PROCEDURE under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS - INTRODUCTION article. If EVAP system SRT is incomplete, turn ignition off, wait at least 5 seconds and go to next step.
  3. Perform driving pattern again. Stop vehicle and select MODE 3 on scan tool. If DTC P0440 or P1447 is set, perform appropriate diagnostic procedure. If DTC P0440 or P1447 is not set, go back to step 2 .

Malfunction is detected when ECM receives a varied signal from fuel level sensor while vehicle is parked. Possible causes are

  1. Fuel level sensor circuit open or shorted.
  2. Defective fuel level sensor.

To confirm presence of DTC, turn ignition on. Select DATA MONITOR with scan tool. Start engine and wait no more than 2 minutes.

Note. Use thew following test to check overall function of fuel level sensor. During this test, DTC may not be confirmed.

Malfunction is detected when fuel level sensor output does not change when vehicle has been driven a long distance. Possible causes are

  1. Fuel level sensor circuit open or shorted.
  2. Defective fuel level sensor.
  1. To check overall function of fuel level sensor circuit, release fuel system pressure. See FUEL SYSTEM in BASIC DIAGNOSTIC PROCEDURES article. Remove fuel feed hose from fuel level sensor unit located behind access cover under rear seat.
  2. Connect a fuel hose to fuel level sensor unit. Place other end of hose into a suitable fuel container. Turn ignition off. Set voltmeter probes between ground and ECM terminal No. 45 (fuel level sensor signal) by basckprobing. See Turn ignition on and monitor voltmeter.
  3. Using suitable equipment, drain 7.93 gals. (30.0 L) of fuel from tank. Refill tank with drained fuel. Voltage should change more than .03 volt during draining and refilling.

DTC Confirmation Procedure

Malfunction is detected when ECM receives an excessively low or high voltage from fuel level sensor. Possible causes are

  1. Fuel level sensor circuit open or shorted.
  2. Defective fuel level sensor.

To confirm presence of DTC, turn ignition on. Select DATA MONITOR with scan tool. Wait at least 5 seconds.

Note. Use the following test to check overall function of VSS circuit. During this test, DTC may not be confirmed.

Malfunction is detected when zero MPH signal is sent to ECM while vehicle is moving. Possible causes are

  1. VSS circuit open or shorted.
  2. Defective VSS.

Depending on equipment available, use one of the following to check function of VSS circuit

  1. Using Scan Tool Raise drive wheels and support vehicle. Start engine. With transmission in a forward gear and wheels turning at 6 MPH, select MODE 1 and check VSS output signal. VSS output signal should be 6 MPH.
  2. Using MIL Raise drive wheels, and support vehicle. Connect an oscilloscope between ground and ECM terminal No. 26 by backprobing. see scheme 2 Start engine. Shift transmission into a forward gear. Increase engine speed until drive wheels are rotating at 25 MPH. VSS signal should be as shown. (Scheme 1)

Scheme 1

Scheme 1
Scheme 1

Malfunction is detected when IACV-AAC valve does not operate properly. Possible causes are

  1. IACV-AAC valve circuit open.
  2. Defective IACV-AAC valve.

Depending on equipment available, use one of the following to set DTC

  1. Using Scan Tool Turn ignition on and wait at least 2 seconds. Select MODE 7.
  2. Using MIL Turn ignition on and wait at least 2 seconds. Turn ignition off and wait at least 5 seconds. Turn ignition on and retrieve DTCs using MIL. See SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS - INTRODUCTION article.

Malfunction is detected when IACV-AAC valve does not operate properly. Possible causes are

  1. IACV-AAC valve circuit shorted.
  2. Defective IACV-AAC valve.

Depending on equipment available, use one of the following to set DTC

  1. Using Scan Tool Start engine and warm to normal operating temperature. Turn ignition off and wait at least 5 seconds. Start engine and let it idle for at least one minute. Select MODE 7 on scan tool.
  2. Using MIL Start engine and warm to normal operating temperature. Turn ignition off and wait at least 5 seconds. Start engine and let it idle for at least one minute. Turn ignition off and wait at least 5 seconds. Turn ignition on and retrieve DTCs using MIL. See SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS - INTRODUCTION article.

Note. Use the following test to check overall function of closed TP switch circuit. During this test, DTC may not be confirmed.

Malfunction is detected when battery voltage is sent to ECM from closed TP switch when throttle valve is opened. Possible causes are

  1. Closed TP switch circuit shorted.
  2. Defective closed TP switch.
  3. Defective TP sensor.

To check overall function of closed TP switch circuit, start engine and warm to normal operating temperature. Measure voltage between ground and ECM terminal No. 27 by backprobing. see scheme 2 Battery voltage should exist at idle. At 2000 RPM, about zero volts should exist.

Note. Use the following test to check overall function of A/T control circuits. During this test, DTC may not be confirmed.

A/T control circuits are used to control shifting during hard acceleration or deceleration. Malfunction is detected when ECM receives incorrect voltage from Transmission Control Module (TCM) continuously. Only possible cause is an open or short in circuit between ECM and TCM.

To check overall function of A/T control circuits, start engine. Measure voltage between ground and ECM terminals No. 24 and 29 by backprobing. see scheme 2 Voltage should be about 7 volts.

Malfunction is detected when ECM calculation function is malfunctioning. Only possible cause is a faulty ECM.

Depending on equipment available, use one of the following to set DTC

  1. Using Scan Tool Start engine and let it idle for at least 30 seconds. Select MODE 7.
  2. Using MIL Start engine and let it idle for at least 30 seconds. Turn ignition off and wait at least 5 seconds. Turn ignition on and retrieve DTCs using MIL. See SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS - INTRODUCTION article.

Note. For best results, perform test with ambient temperature at 14°F (-10°C) or more and engine coolant temperature 14-140°F (-10-60°C).

Malfunction is detected when engine coolant temperature does not reach a specified temperature, even though engine has been running for a specified time. Possible causes are

  1. Stuck open thermostat.
  2. Thermostat seal leaking.
  3. Defective Engine Coolant Temperature (ECT) sensor.

To confirm presence of DTC, replace thermostat using an OEM thermostat. Turn ignition on. Select DATA MONITOR with scan tool and observe engine coolant temperature. Ensure engine coolant temperature is less than 140°F (60°C). Drive vehicle at 50-75 MPH for 10 minutes.

Note. Use the following test to check overall function of closed-loop fuel control. During this test, DTC may not be confirmed.

Malfunction is detected when ECM does not operate in closed loop. Possible causes are

  1. Front Heated Oxygen Sensor (HO2S) circuit open or shorted.
  2. Defective front HO2S.
  3. Defective front HO2S heater.

To check closed-loop operation, start engine and warm to normal operating temperature. Measure voltage between engine ground and ECM terminal No. 46 by backprobing. see scheme 2 Monitor voltmeter with engine at 2000 RPM. Voltage should be less than.21 volt at least once and more than.70 volt at least once.

Malfunction is detected when ECM does not receive signal from ignition primary circuit during engine cranking or running. Possible causes are

  1. Ignition primary circuit open or shorted.
  2. Defective power transistor.
  3. Defective resistor.
  4. Faulty Camshaft Position (CMP) sensor or circuit.

Depending on equipment available, use one of the following to set DTC

  1. Using Scan Tool Start engine. If engine will not start, crank engine for at least 5 seconds. Select MODE 7 on scan tool.
  2. Using MIL Start engine. If engine will not start, crank engine for at least 5 seconds. Turn ignition off and wait at least 5 seconds. Turn ignition on and retrieve DTCs using MIL. See SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS - INTRODUCTION article.

Malfunction is detected when ECM receives an improper voltage signal through EGRC solenoid. Possible causes are

  1. EGRC solenoid circuit open or shorted.
  2. Defective EGRC solenoid.

Depending on equipment available, use one of the following to set DTC

  1. Using Scan Tool Turn ignition on and wait at least 5 seconds. Select MODE 7.
  2. Using MIL Turn ignition on and wait at least 5 seconds. Turn ignition off and wait at least 5 seconds. Turn ignition on and retrieve DTCs using MIL. See SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS - INTRODUCTION article.

Malfunction is detected when EGR temperature sensor voltage is low when engine coolant temperature is low. Possible causes are

  1. EGR temperature sensor circuit shorted.
  2. Defective EGR temperature sensor.
  3. EGR system not functioning properly.
  4. Defective EGR Control Backpressure Transducer (EGRC-BPT).
  5. Defective EGR Control (EGRC) solenoid.

Depending on equipment available, use one of the following to set DTC

  1. Using Scan Tool Turn ignition on and select MODE 1 on scan tool. Ensure engine coolant temperature is less than 104°F (40°C). If engine temperature is more than specified, allow engine to cool. Start engine and let it idle for at least 8 seconds. Select MODE 7 on scan tool.
  2. Using MIL Turn ignition on. Measure voltage between ground and ECM terminal No. 51 (engine coolant temperature sensor signal) by backprobing. see scheme 2 If voltage is 2.7 volts or less, allow engine to cool. Start engine and let it idle for at least 8 seconds. Turn ignition off and wait at least 5 seconds. Turn ignition on and retrieve DTCs using MIL. See SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS - INTRODUCTION article.

DTC Confirmation Test "B" (Overall Function Check)

Note. Use the following test to check overall function of EGR temperature sensor. During this test, DTC may not be confirmed.

Malfunction is detected when EGR temperature sensor voltage is high when engine coolant temperature is high. Possible causes are

  1. EGR temperature sensor circuit open.
  2. Defective EGR temperature sensor.
  3. EGR system not functioning properly.
  4. Defective EGR Control Backpressure Transducer (EGRC-BPT).
  5. Defective EGR Control (EGRC) solenoid.
  1. To check overall function of EGR temperature sensor, start engine and warm to normal operating temperature. Let engine idle for at least 2 minutes. Ensure EGR valve is not open. If EGR valve is open, go to «DTC P1402: EGR FUNCTION»(ref-2731-S23972255082000041200000). If EGR valve is not open, go to next step.
  2. Measure voltage between ground and ECM terminal No. 62 (EGR temperature sensor signal) by backprobing. see scheme 2 With engine speed raised to 1500 RPM, open EGR valve by hand. Voltage should decrease to less than one volt. If voltage is as specified, perform diagnosis for DTC P0400 and P1400. See «DTC P0400: EGR FUNCTION»(ref-2731-S03558155842000041200000) and «DTC P1400: EGR CONTROL (EGRC) SOLENOID»(ref-2731-S14085039442000041200000). If voltage is not as specified, go to «PROCEDURE»(ref-2731-S42787190272000041200000).

Malfunction is detected when EGR flow is detected under conditions that do not call for EGR. Possible causes are

  1. Defective EGR Control (EGRC) solenoid.
  2. EGR valve stuck open or leaking.
  3. Defective EGR temperature sensor.
  4. Defective EGR Control Backpressure Transducer (EGRC-BPT).

Depending on equipment available, use one of the following to set DTC

  1. Using Scan Tool Turn ignition on and select MODE 1 on scan tool. Ensure engine coolant temperature is 14-104°F (-10-40°C) and EGR temperature sensor voltage is less than 4.8 volts. Start engine and let it idle for at least 70 seconds. Turn ignition off and wait at least 5 seconds. Repeat previous steps. Turn ignition on and select MODE 3 on scan tool.
  2. Using MIL Turn ignition on. Measure voltage between ground and ECM terminal No. 51 (engine coolant temperature sensor signal) by backprobing. see scheme 2 Ensure voltage is 2.7-4.4 volts. Measure voltage between ground and ECM terminal No. 62 (EGR temperature sensor signal) by backprobing. Ensure voltage is less than 4.8 volts. Start engine and let it idle for at least 70 seconds. Turn ignition off and wait at least 5 seconds. Turn ignition on and retrieve DTCs using MIL. See SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS - INTRODUCTION article.

Note. Before performing test, ensure ambient temperature is 32°F (0°C) or more.

Malfunction is detected when canister purge flow is detected when EVAP-CPVCV is closed. Possible causes are

  1. Defective EVAP Control System Pressure Sensor (EVAP-CSPS).
  2. EVAP-CPVCV stuck open.
  3. Defective EVAP Canister Vent Control Valve (EVAP-CVCV).
  4. Defective EVAP canister.
  5. EVAP system hoses misrouted or plugged.

Depending on equipment available, use one of the following to set DTC

  1. Using Scan Tool Start engine and warm to normal operating temperature. Turn ignition off and wait at least 5 seconds. Start engine and let it idle for at least 10 seconds. Select MODE 7 on scan tool.
  2. Using MIL Start engine and warm to normal operating temperature. Turn ignition off and wait at least 5 seconds. Start engine and let it idle for at least 10 seconds. Turn ignition off and wait at least 5 seconds. Turn ignition on and retrieve DTCs using MIL. See SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS - INTRODUCTION article.

Malfunction is detected when EVAP-CVCV remains closed under certain driving conditions. Possible causes are

  1. Defective EVAP-CVCV.
  2. Faulty EVAP Control System Pressure Sensor (EVAP-CSPS) or circuit.
  3. Blockage in hose to EVAP-CVCV.
  4. Defective water separator.
  5. EVAP canister saturated with water.

Depending on equipment available, use one of the following to set DTC

  1. Using Scan Tool Start engine. Drive vehicle at a speed of about 50 MPH for 15 minutes. Select MODE 7 on scan tool.
  2. Using MIL Start engine. Drive vehicle at a speed of about 50 MPH for 15 minutes. Turn ignition off and wait at least 5 seconds. Turn ignition on and retrieve DTCs using MIL. See SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS - INTRODUCTION article.

Note. Use the following test to check overall function of EVAP purge flow monitoring system. During this test, DTC may not be confirmed.

Malfunction is detected when EVAP system is not functioning properly or there is a leak in hose between EVAP Control System Pressure Sensor (EVAP-CSPS) and intake manifold. Possible causes are

  1. EVAP Canister Purge Volume Control Valve (EVAP-CPVCV) stuck closed.
  2. Faulty EVAP-CSPS or circuit.
  3. Blockage or leak in hoses.
  4. EVAP canister cracked.
  5. Fault in EVAP-CPVCV circuit.
  6. Defective closed Throttle Position (TP) switch.
  7. Plugged purge port.
  8. Defective EVAP Canister Vent Control Valve (EVAP-CVCV).

To check overall function of purge flow monitoring system, start engine and warm to normal operating temperature. Turn ignition off and wait at least 5 seconds. Start engine and wait at least 70 seconds. With engine idling, measure and record voltage between ECM terminal No. 67 (EVAP-CSPS signal) and ground by backprobing. see scheme 2 Raise drive wheels and support vehicle. While monitoring voltage, maintain the following conditions for at least one minute

  1. A/C on.
  2. Steering wheel turned fully.
  3. Headlights on.
  4. Engine speed at 3000 RPM.
  5. Rear window defogger on.
  6. Transmission in any forward gear.

Ensure voltage remains .1 volt less than voltage measured at idle for at least one second.

Note. Use the following test to check overall function of EVAP-CVCV. During this test, DTC may not be confirmed.

Malfunction is detected when EVAP-CVCV remains open under certain driving conditions. Possible causes are

  1. Defective EVAP-CVCV.
  2. Faulty EVAP Control System Pressure Sensor (EVAP-CSPS) or circuit.
  3. Blockage in EVAP-CVCV hose.
  4. Defective water separator.
  5. EVAP canister saturated with water.
  6. Defective vacuum cut valve.

To check overall function of EVAP-CVCV, disconnect hose from water separator. see scheme 14 Disconnect EVAP-CVCV harness connector. Using jumper wires, apply battery voltage and ground to EVAP-CVCV terminals. see scheme 17 Air should not flow through EVAP-CVCV. Remove jumper wires. Air should flow. If operation is as specified, go to DTC P0440: EVAP CONTROL SYSTEM (SMALL LEAK - NEGATIVE PRESSURE) OR DTC P1441: EVAP CONTROL SYSTEM (VERY SMALL LEAK). If operation is not as specified, go to PROCEDURE.

Malfunction is detected when ECM receives a high voltage from fuel level sensor. Possible causes are

  1. Fuel level sensor circuit open or shorted.
  2. Defective fuel level sensor.

To confirm presence of DTC, turn ignition on. Select DATA MONITOR with scan tool. Wait at least 5 seconds.

Malfunction is detected when an improper voltage signal is sent to ECM through vacuum cut valve by-pass valve. Possible causes are

  1. Vacuum cut valve by-pass valve circuit open or shorted.
  2. Defective vacuum cut valve by-pass valve.

Depending on equipment available, use one of the following to set DTC

  1. Using Scan Tool Start engine and run for at least 5 seconds. Select MODE 7 on scan tool.
  2. Using MIL Start engine and run for at least 5 seconds. Turn ignition off and wait at least 5 seconds. Turn ignition on and retrieve DTCs using MIL. See SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS - INTRODUCTION article.

Note. Use the following test to check overall function of vacuum cut valve by-pass valve. During this test, DTC may not be confirmed.

Malfunction is detected when vacuum cut valve by-pass valve does not operate properly. Possible causes are

  1. Defective vacuum cut valve by-pass valve.
  2. Defective vacuum cut valve.
  3. Blockage in by-pass hoses.
  4. Faulty EVAP Control System Pressure Sensor (EVAP-CSPS) or circuit.
  5. Defective EVAP Canister Vent Control Valve (EVAP-CVCV).
  6. Blockage in hoses between fuel tank and vacuum cut valve.
  7. Blockage in hoses between EVAP canister and vacuum cut valve.
  8. Defective EVAP canister.

To check overall function of vacuum cut valve by-pass valve, perform step 1 of PROCEDURE.

Malfunction is detected when ECM receives incorrect voltage from Transmission Control Module (TCM). Possible causes are

  1. Communication line between ECM and TCM open or shorted.
  2. Weak battery.
  3. Defective TCM.

Depending on equipment available, use one of the following to set DTC

  1. Using Scan Tool Start engine and let it idle for at least 40 seconds. Select MODE 7.
  2. Using MIL Start engine and let it idle for at least 40 seconds. Turn ignition off and wait at least 5 seconds. Turn ignition on and retrieve DTCs using MIL. See SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS - INTRODUCTION article.

Note. Use the following test to check overall function of PNP switch circuit. During this test, DTC may not be confirmed.

Malfunction is detected when PNP switch signal does not change between starting and driving. Possible causes are

  1. PNP switch circuit open or shorted.
  2. Circuit between ECM and TCM open or shorted.
  3. Defective PNP switch.
  4. Defective TCM.

To check overall function of PNP switch circuit, turn ignition on. Measure voltage between ECM terminal No. 22 and body ground by backprobing. see scheme 1and see scheme 2. With transmission in Park (A/T only) or Neutral, about zero volts should exist. With transmission in any other gear, about 5 volts should exist.

Note. Use the following test to check overall function of cooling fan circuit. During this test, DTC may not be confirmed.

Malfunction is detected when engine coolant reaches an abnormally high temperature. To check overall function of cooling fan circuit, allow engine to cool. Check coolant level in radiator and reservoir tank. If coolant level is low, go to PROCEDURE. If coolant level is okay, start engine. Turn A/C and blower on. Set controls for maximum cooling. Let engine idle for a few minutes. Cooling fan should operate at low speed. Turn ignition off. Turn A/C and blower off. Disconnect Engine Coolant Temperature (ECT) sensor harness connector. see scheme 6 Connect a 150-ohm resistor across ECT sensor harness connector terminals. Start engine and ensure cooling fan operates at high speed.

More articles — Engine Controls - Self-Diagnostics - 2.4