System Description

MIL:

CHECK ENGINE/MALFUNCTION INDICATOR LAMP
As a functional test, the Malfunction Indicator Lamp (MIL) illuminates at key-on before engine cranking. Whenever the Powertrain Control Module (PCM) sets a diagnostic trouble code that effects vehicle emissions, it illuminates the MIL. The PCM illuminates the MIL only for diagnostic trouble codes that effect vehicle emissions. The MIL remains on until the diagnostic trouble code is erased. The MIL either flashes or illuminates continuously when the PCM detects active engine misfire.

During active misfire, the PCM records the current engine operating conditions. The engine operating conditions are recorded by the PCM.

ON-BOARD DIAGNOSTICS
The Powertrain Control Module (PCM) monitors many different circuits in the fuel injection system. If the PCM senses a problem with a monitored circuit often enough to indicate an actual problem, it stores a diagnostic trouble code in the PCM's memory.

After the PCM first detects a malfunction, a diagnostic trouble code is recorded when the engine is restarted and the same malfunction is re-detected. However, for items marked with a "*", a diagnostic trouble code is recorded on the first detection of the malfunction.

After that, if the PCM does not re-detect the malfunction for 40 drives* (51 engine starts for non-emission related faults), the diagnostic trouble code will be erased from the PCM memory.

NOTE: * A drive indicates from engine start to stop and monitors the powertrain component.

However, for misfiring or a fuel system rich/lean, the diagnostic trouble codes will be erased under the following conditions.
- When driving conditions (engine speed, engine coolant temperature, etc.) are similar to those when the malfunction was first recorded.
- When the ROM does not re-detect the malfunction for 80 drives*.

Technicians can display stored diagnostic trouble codes by two different methods:
The first is to cycle the ignition switch On-Off-On-Off-On within 5 seconds. Then count the number of times the malfunction indicator lamp (check engine lamp) on the instrument panel flashes on and off. The number of flashes represents the diagnostic trouble code. There is a slight pause between the flashes representing the first and second digits of the code. Longer pauses separate individual trouble codes. The second method of reading diagnostic trouble codes uses the scan tool. Connect the scan tool to the data link (diagnostic) connector in the vehicle.