CHECK ENGINE LIGHT
All models are equipped with a malfunction indicator (CHECK ENGINE) light. When the CHECK ENGINE light remains on, the self-diagnostic system has detected a system failure.
HARD FAILURES
Hard failures cause CHECK ENGINE light to glow. Fault codes are stored in Electronic Control Module (ECM) memory. All codes except Codes 26 and 44 will cause CHECK ENGINE light to remain illuminated (with ignition on) until fault is corrected and ECM memory is cleared.
Codes 26 and 44 and the CHECK ENGINE light will remain on only until next ignition on/off cycle. Code will no longer be available to driver, but will still be stored in ECM memory.
If light comes on and remains on during vehicle operation, cause of malfunction must be determined using TROUBLE CODE IDENTIFICATION table. 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 poor driveability may occur.
RETRIEVING CODES
When a system fault has been detected, trouble codes can be retrieved. Vehicle must be stationary. With ignition switch in OFF position, wait 5 seconds and then turn ignition switch to position II. DO NOT start engine. On XJ6, press Vehicle Condition Monitor (VCM) button, located on VCM/trip computer display panel. VCM/trip computer display panel is located below tachometer and speedometer. On XJS, pressing VCM button is not required.
Applicable trouble code will be displayed on display panel. See appropriate code in TROUBLE CODE IDENTIFICATION table below for probable cause. When engine is started, trouble code will be deleted from written display, but the CHECK ENGINE light will remain on.
CLEARING CODES
Turn ignition switch to OFF position. Remove negative battery cable for at least 30 seconds to clear ECM trouble code memory.
SUMMARY
If no hard fault codes are present, see TESTS W/O CODES article in this section for diagnosis by symptom (i.e., ROUGH IDLE, NO START, etc.) or intermittent diagnostic procedures.