Malfunction Indicator Light

The Malfunction Indicator Light (MIL) is located on instrument panel and is labeled CHECK ENGINE. The MIL will illuminate if the ECM detects a failure of a OBD-II emission related component. When this occurs, a Diagnostic Trouble Code (DTC) will be set into ECM memory.

When a malfunction has been detected in 2 consecutive drive cycles, the ECM will turn on the MIL and store a DTC in memory. One exception is if a misfire malfunction is detected that may damage catalytic converter, the MIL will illuminate or flash immediately and DTC will be set. If the same malfunction is not detected for 3 consecutive drive cycles the ECM will turn MIL off. The DTC will remain in ECM memory for 40 drive cycles, if fault does not recur DTC will be purged from ECM memory.

If MIL remains on during engine cranking, it could indicate the ECM is not receiving CMP signal or the MIL circuit is shorted to ground. If MIL blinks there may be a severe misfire being detected by ECM. To turn MIL off after a repair, a ECM reset command from the scan tool must be sent, or 3 consecutive drive cycles must be completed without any detected malfunction. See DRIVE CYCLES . If MIL never illuminates, check MIL circuit for opens and shorts. See the WIRING DIAGRAMS article.