Diagnostic System
NOTE:
A "CHECK ENGINE" lamp driver is installed in the wiring harness from ECM to the "CHECK ENGINE" lamp. This driver amplifies the power to the "CHECK ENGINE" lamp to reduce amperage draw on the battery.
The ECM of the CEC system is equipped with a self-diagnostic system which detects system failures or abnormalities. When a malfunction occurs, the ECM will light the "CHECK ENGINE" lamp, located on the instrument panel. When the malfunction is detected and the lamp is turned on, a corresponding trouble code will be stored in ECM memory. Malfunctions are recorded as "hard failures" or as "intermittent failures".
- "Hard failures" cause the "CHECK ENGINE" lamp to glow and remain on until the malfunction is repaired. If the "CHECK ENGINE" lamp comes on and remains on during vehicle operation, the cause of the malfunction must be determined.
- "Intermittent failures" cause the "CHECK ENGINE" lamp to flicker or go out after about 10 seconds when the fault goes away. However, the corresponding trouble code will be retained in ECM memory. "Intermittent failures" may be sensor related. If a sensor fails, the 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 fault does not reoccur within 50 engine starts, the related trouble code will be erased from ECM memory.
As a bulb and system check, the "CHECK ENGINE" lamp will glow when the ignition switch is turned on and the engine is not running. When the engine is started, the lamp should go out. If not, a malfunction has been detected in the CEC system.
NOTE:
Trouble codes will be recorded at various operating times. Some codes require operation of that sensor or switch for 5 seconds; others require operation for 5 minutes or longer.