On-Board Diagnostics

When ignition is first turned on, Malfunction Indicator Light (MIL) illuminates for approximately 2 seconds to verify bulb and circuit operation, and then go off. The MIL (CHECK ENGINE light) is located on instrument panel.

NOTE: MIL cannot be used to retrieve Diagnostic Trouble Codes (DTCs).

When Powertrain Control Module (PCM) detects a Diagnostic Trouble Code (DTC) that affects vehicle emissions, MIL is illuminated. If a problem is detected by PCM, PCM sends a message over a Bus line to turn on MIL in instrument cluster.

PCM will only illuminate MIL for failures which affect vehicle emissions. If MIL is on continuously, PCM has entered a Limp-In mode, identified a failed emission component or system. MIL will remain on until cleared using scan tool. MIL will either remain on continuously or flash when PCM detects an active engine misfire. PCM will turn off MIL if:

PCM does not detect the malfunction for 3 consecutive trips (except for misfire and fuel system monitors).
PCM does not detect a malfunction while performing 3 consecutive engine misfire or fuel system tests. PCM performs these tests when engine is operating within plus or minus 375 RPM of and within 10 percent engine load of operating condition when malfunction was first detected.

The Powertrain Control Module (PCM) monitors several different engine control system circuits. If PCM detects a malfunction on a monitored circuit often enough to indicate a problem, a Diagnostic Trouble Code (DTC) will be stored in PCM memory.

The PCM also records and stores engine operating conditions when malfunction occurred. This information is referred to as freeze frame data. If malfunction is an engine misfire, or fuel system rich or fuel system lean condition, freeze frame data will be updated with the most current information regarding these failures.

DTCs may be retrieved for system diagnosis. See RETRIEVING DIAGNOSTIC TROUBLE CODES under SELF-DIAGNOSTIC SYSTEM.