MALFUNCTION INDICATOR LIGHT
A Malfunction Indicator Light (MIL) informs the driver of system problems. MIL will come on as a bulb check when ignition switch is in ON position and engine is not running. MIL should go out when engine starts. If MIL remains on or flashes with the engine running, the self-diagnostic system has detected a problem.
Hard Failures
A hard failure will cause MIL to come on and remain on until the malfunction is repaired. If MIL comes on and remains on (or flashes) during vehicle operation, cause of malfunction must be determined using diagnostic code charts.
If a sensor fails, PCM will use a substitute value in its calculations to continue engine operation. In this condition, commonly known as limp-in mode, vehicle is functional but driveability may be affected.
Intermittent Failures
Intermittent failures may cause MIL to come on or flicker. Light will go out after fault disappears. The corresponding trouble code will be retained in Powertrain Control Module (PCM) memory. Intermittent failures may be caused by sensor, connector, or wiring problems. See INTERMITTENTS in TESTS W/O CODES article.
CLEARING CODES
Turn ignition off. Use scan tool to clear codes or disconnect negative battery cable for a minimum of 20 seconds. DTCs are now cleared. Reconnect battery cable.
Note. Turn ignition off before disconnecting or reconnecting battery power to PCM. When battery power is disconnected from PCM to clear codes, computer memory will be erased. A change in vehicle performance and driveability may be noted while PCM recalibrates for current driving conditions.
AFTER-REPAIR PROCEDURE
After indicated service or replacement is performed, clear codes. See CLEARING CODES . Start engine. Ensure engine is at normal operating temperature. Raise engine speed to 2000 RPM for 3 minutes. Recheck for codes. No codes should be present. If any codes are present, perform appropriate diagnostic code test under appropriate DIAGNOSTIC TESTS .
SUMMARY
If no fault 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 procedures.