Mitsubishi Galant/Mirage/Diamante 1990-2000

General Information


The Powertrain Control Module (PCM) monitors the signals of input and output sensors, some all the time and others at certain times and processes each signal. When the PCM notices that an irregularity has continued for a specified time or longer from when the irregular signal was initially monitored, the PCM judges that a malfunction has occurred and will memorize the malfunction code. The code is then stored in the memory of the PCM and is accessible through the data link (diagnostic connector) with the use of an electronic scan tool or a voltmeter.


Among the on-board diagnostic items, a check engine/malfunction indicator light comes on to notify the driver of a emission control component irregularity. If the irregularity detected returns to normal or the PCM judges that the component has returned to normal, the check engine/malfunction indicator light will be turned off. Moreover, if the ignition is turned OFF and then the engine is restarted, the check engine/malfunction indicator light will not be turned on until a malfunction is detected.

The check engine/malfunction indicator light will come on immediately after the ignition switch is turned ON . The light should stay lit for 5 seconds and then will go off. This indicates that the check engine/malfunction indicator lamp is operating normally. This does not signify a problem with the system.

The check engine/malfunction indicator lamp will come on when the terminal for the ignition timing adjustment is shorted to ground. Therefore, it is not abnormal that the light comes on even when the terminal for ignition timing is shorted at time of ignition timing adjustment.

To test the light, perform the following:

  1. Turn the ignition switch ON . Inspect the check engine/malfunction indicator lamp for illumination.
  3. The light should be lit for 5 seconds and then should go out.
  5. If the lamp does not illuminate, check for open circuit in the harness, blown fuse or blown bulb.


Before attaching or detaching the PCM harness connectors, make sure the ignition switch is OFF and the negative battery cable is disconnected to avoid the possibility of damage to the PCM.
When performing PCM input/output signal diagnosis, remove the pin terminal retainer from the connectors to make it easier to insert tester probes into the connector.
When attaching or detaching pin connectors from the PCM, take care not to bend or break any pin terminals. Check that there are no bends or breaks on PCM pin terminals before attempting any connections.
Before replacing any PCM, perform the PCM input/output signal diagnosis to make sure the PCM is functioning properly.
When measuring supply voltage of PCM-controlled components with a circuit tester, separate 1 tester probe from another. If the 2 tester probes accidentally make contact with each other during measurement, a short circuit will result and damage the PCM.