Hard Failures
Hard failures cause Malfunction Indicator Light (MIL) to illuminate and remain on until problem is repaired. If light comes on and remains on (light may flash) during vehicle operation, cause of malfunction must be determined by retrieving DTCs and using TROUBLE CODE CHARTS. See RETRIEVING CODES . If a sensor fails, control unit will use a substitute value in its calculations to continue engine operation. In this condition, commonly known as limp-in mode, the vehicle runs but driveability will not be optimum.
Intermittent Failures
Intermittent failures may cause Malfunction Indicator light (MIL) to flicker or illuminate and go out after the intermittent fault goes away. The corresponding DTC will be retained in ECM memory. If related fault does not reoccur within 50 starter operations, related DTC 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.
MALFUNCTION INDICATOR LIGHT (MIL)
All models are equipped with an MIL. As a bulb check, light illuminates when ignition is on and engine is not running. MIL also illuminates when a system failure has been detected and a corresponding DTC has been set in ECM memory. Not all trouble codes will activate MIL. If MIL is on and no DTCs are in memory, problem may be intermittent. See INTERMITTENTS in TESTS W/O CODES article.
RETRIEVING CODES
Turn ignition off. Insert jumper wire in service check connector, located behind center console. (Scheme 54)
Turn ignition on. Diagnostic Trouble Codes (DTCs) will be indicated by a series of long and short flashes on MIL. The number of long flashes indicates the number in the 10s column. The number of short flashes indicates the number in the 1s column. For example, 4 long flashes followed by 3 short flashes would indicate DTC 43.
See DIAGNOSTIC TROUBLE CODE IDENTIFICATION TABLE and proceed to appropriate TROUBLE CODE CHART for testing. All voltage tests should be performed with a Digital Volt-Ohmmeter (DVOM) with a minimum 10-megohm input impedance, unless specifically stated differently in testing procedure.
Scheme 54
SUMMARY
If no hard trouble codes (or only pass codes) are present, driveability symptoms exist or intermittent codes exist, proceed to TESTS W/O CODES article for diagnosis by symptom (i.e., ROUGH IDLE, NO START, etc.) or intermittent diagnostic procedure.