Engine Malfunction Test

This test is constantly performed by the ECM to detect system failures or malfunctions. When a malfunction occurs, ECM will light the "ENGINE CONTROL SYSTEM FAULT" light. When a malfunction occurs and lamp is turned on, a corresponding trouble code is stored in ECM memory. Trouble codes for ECM, BCM, Lighting and Anti-Lock Brakes may be displayed on the CCDIC by entering the "Diagnostic Mode". See RETRIEVING STORED TROUBLE CODES  .

Malfunctions are recorded as "hard failures" or "intermittent failures".

• "Hard failures" cause "ENGINE CONTROL SYSTEM" fault light to glow and remain on until malfunction is repaired. If the "ENGINE CONTROL SYSTEM" fault light comes on and remains on during vehicle operation, cause of malfunction MUST be determined.
• "Intermittent failures" cause "ENGINE CONTROL SYSTEM" fault light to flicker or go out after malfunction clears. "Intermittent failures" may be sensor related. If a sensor fails, ECM will use a substitute value in its calculations to continue engine operation. In this condition, service is not mandatory; but loss of driveability may be encountered and "SERVICE SOON" light may be illuminated. If the sensor malfunction does not recur within 50 ignition cycles, related trouble code will be erased from ECM memory.

As a light and system check, "ENGINE CONTROL SYSTEM" lights should glow when engine is in cranking mode and go out after engine starts. If not, ECM has detected fault in system.

When a "hard" malfunction is detected at the same time as an "intermittent" malfunction, only the "SERVICE NOW" light will glow. The "ENGINE CONTROL SYSTEM" light will glow when the system is in the diagnostic mode.