Engine Malfunction Test

This test is constantly performed by ECM to detect system failures or malfunctions. When a malfunction occurs, ECM will light the "SERVICE NOW/SOON" light. When a malfunction occurs and lamp is turned on, a corresponding trouble code is stored in ECM memory. Malfunctions are recorded as "hard failures" or "intermittent failures".

• "Hard failures" cause "SERVICE NOW/SOON" light to glow and remain on until malfunction is repaired. If the "SERVICE NOW/SOON" light comes on and remains on during vehicle operation, cause of malfunction MUST be determined.
• "Intermittent failures" cause "SERVICE NOW/SOON" 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. If the related sensor malfunction does not recur within 50 ignition cycles, related trouble code will be erased from ECM memory.

As a lamp and system check, "SERVICE NOW/SOON" 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 "SERVICE NOW" malfunction is detected at the same time a "SERVICE SOON" malfunction is detected, only the "SERVICE NOW" light will glow. Both lights will glow when the system is displaying the diagnostic routine.