HARD FAILURES
Hard failures cause CHECK ENGINE light to illuminate and remain on until the malfunction is repaired. If light comes on and remains on (light may flash) during vehicle operation, cause of malfunction must be determined using diagnostic (code) charts. If a sensor fails, control unit will use a substitute value in its calculations to continue engine operation. In this condition, vehicle is functional, but loss of good driveability will most likely be encountered.
INTERMITTENT FAILURES
Intermittent failures may cause CHECK ENGINE light to flicker or illuminate and go out after the intermittent fault goes away. The corresponding trouble code, however, will be retained in control unit memory. If related fault does not reoccur within a certain time frame, related trouble code 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.
CLEARING CODES
Disconnect negative battery cable for at least 5 seconds. Reconnect battery cable. Ground test connector with jumper wire. Turn ignition on and verify no codes are displayed.
CODE 14: (ATMOSPHERIC PRESSURE SENSOR)
- Replace ECU
Scheme 19
Scheme 20
Scheme 21
Scheme 22
SUMMARY
If no hard fault 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 procedures.