MALFUNCTION INDICATOR LIGHT
Note. Loose fuel cap will cause MIL to illuminate.
The Electronic Control Module (ECM) is equipped with a self-diagnostic system, which detects system failures or abnormalities. When a malfunction that may affect vehicle emissions is detected during 2 sequential drive cycles, the ECM will illuminate the Malfunction Indicator Light (MIL) on the instrument panel. (Схема №1) A corresponding Diagnostic Trouble Code (DTC) will be stored in ECM. If a misfire is detected, MIL will illuminate and DTC will be stored in ECM immediately after fault is detected. If misfire is severe enough to cause catalytic converter damaged, MIL will blink. MIL will continuously blink until danger to catalytic converter has passed. To retrieve stored DTC(s), see RETRIEVING DIAGNOSTIC TROUBLE CODES.
DTC will be erased from ECM memory. If battery is disconnected, all DTCs and freeze frame data will be erased from ECM. As a bulb check, Malfunction Indicator Light (MIL) will also illuminate for about 5 seconds when ignition is turned on.
DTCs will be recorded at various operating times and conditions. Some DTCs require operation of sensor or switch for 5 seconds, while other components require operation for 5 minutes or longer at normal operating temperature, vehicle speed, and load. Therefore, when verifying repair, some DTCs may not set in a service bay and may require road testing to duplicate the conditions under which the code will set.
SERVICE PRECAUTIONS
Before proceeding with diagnosis, following precautions must be observed
- Ensure vehicle has a fully charged battery and functional charging system.
- Visually inspect connectors and circuit wiring being worked on.
- DO NOT disconnect battery or Engine Control Module (ECM) unless instructed to do so. Doing so will erase any fault codes stored in ECM. Turn ignition off before disconnecting battery or damage to ECM may result.
- DO NOT cause short circuits when performing electrical tests. DO NOT disconnect sensors with ignition on. Either procedure will set additional fault codes, making diagnosis of original problem more difficult.
- DO NOT use a test light in place of a voltmeter.
- When checking for spark, DO NOT hold coil wire more than 1/4" from ground. Damage to vehicle electronics and/or ECM may result.
- DO NOT prolong testing of fuel injectors. Engine may hydrostatically (liquid) lock.
- The control harness between ECM and Heated Oxygen Sensor (HO2S) has a shield grounded to chassis to prevent electromagnetic interference. If shield is damaged, the control harness must be replaced.
FREEZE FRAME DATA
Engine operating conditions are required to be captured and stored in Engine Control Module (ECM) memory whenever a malfunction is detected. Data captured in this manner is called FREEZE FRAME data. Freeze frame data is similar to a single record of operating conditions. Whenever a malfunction is detected, a corresponding record of operating conditions is recorded in the freeze frame buffer.
Freeze frame data can only be overwritten with data associated with a misfire or fuel trim malfunction. Misfire data takes priority over all other data because of its possible part-damaging (oxygen sensors, catalytic converters, etc.) effects. Freeze frame data will not be erased unless associated DTC is cleared from ECM memory.
AFTER-REPAIR PROCEDURE
After repair, clear codes. See CLEARING DIAGNOSTIC TROUBLE CODES . Verify repairs by driving vehicle with scan tool connected to OBD-II DLC and monitoring for pending codes.
READINESS DRIVE CYCLE
Perform Readiness Drive Cycle when directed to from diagnostic tests. Readiness drive cycle provides conditions for EVAP monitor to run, so that repairs for EVAP DTC(s) may be verified.