Engine Controls - Tests W/codes - 5.7L: Other Chevrolet Tahoe I

HARD FAILURES

Most hard failures cause MIL to illuminate and remain on until malfunction is repaired. If MIL comes on and remains on (light may flash) during vehicle operation, cause of malfunction must be determined. See DIAGNOSTIC PROCEDURE .

If a sensor fails, PCM/VCM will use a substitute value in its calculations to continue engine operation. In this condition, vehicle is functional, but it will most likely display degraded driveability.

INTERMITTENT FAILURES

Intermittent failures cause MIL to flicker or glow and go out about 10 seconds after intermittent fault goes away. Corresponding DTC, however, will be retained in PCM/VCM memory. If related fault does not reoccur within 50 engine starts, trouble code will be erased from control module memory. Intermittent failures may be caused by sensor, connector or wiring related problems. See INTERMITTENTS in the TESTS W/O CODES article.

Note. OBD II vehicles have options available in the scan tool DTC mode to display enhanced information available. However, to fully utilize information and procedures requires the use of a Tech 1 or 2 scan tool. See scan tool operator's manual for additional information.

The following are Tech 1 or 2 scan tool sub-menus in the DTC INFO and SPECIFIC DTC modes

FAIL THIS IGN.

This selection will display all DTCs that have failed during the present ignition cycle.

HISTORY

This selection will display only DTC(s) that are stored in the control module's history memory. It will not type "B" DTCs. It will display all type "A" and type "B" DTCs that have the MIL illuminated and have failed within the last 40 warm-up cycles. It will also display type "C" DTCs that have failed within the 40 warm-up cycles.

MIL REQUEST

This selection will display only DTCs that are requesting the MIL. Type "C" DTCs cannot be displayed using this option. This selection will report type "B" DTCs only after the MIL has been requested.

NOT RUN SCC

Not Run Since Code Clear option will display up to 33 DTCs that have not run since DTCs were last cleared. Since any displayed DTCs have not run, their condition (passing or failing) is unknown.

FAILED SINCE CLEAR

This message indicates the DTC has failed at least once within the last 40 warm-up cycles since the last time DTCs were cleared.

NOT RUN SINCE CL.

Not Run Since Cleared message indicates that the selected diagnostic test has not run since the last time DTCs were cleared. Therefore, the diagnostic test status (passed or failed) is unknown. After DTCs are cleared, this message will continue to be displayed until the diagnostic test runs.

NOT RUN THIS IGN.

Not Run This Ignition message indicates the selected diagnostic test has not run this ignition cycle.

SCAN DATA

Note. For scan data values, refer to scan tool manufacturer owner's manual or compare values with a known good component or vehicle.

SUMMARY

If no hard fault codes are present, driveability symptoms exist or intermittent DTC(s) exist, proceed to the TESTS W/O CODES article for diagnosis by symptom (i.e., ROUGH IDLE, NO START, etc.) or intermittent diagnostic procedures.

VCM will run EGR tests when following conditions are present

1. No TP sensor DTCs are set.
2. No MAP sensor DTCs are set.
3. No VSS DTCs are set.
4. No IAT sensor DTCs are set.
5. No ECT sensor DTCs are set.
6. No IAC DTCs are set.
7. No linear EGR pintle position DTCs are set.
8. No transmission DTCs are set.
9. No HVAC DTCs are set.
10. Engine coolant temperature is greater than 172°F (78°C).
11. Baro is greater than 70 kPa (less than 10,3000 ft.).
12. Vehicle speed is greater than 30 MPH.
13. AC clutch status is unchanged.
14. Transmission is in locked or unlocked stage (stable).
15. No misfire DTCs are set.
16. Engine speed is 1000-1600 RPM.