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.
CHECK ENGINE/MALFUNCTION INDICATOR LIGHT
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.
To test the light, perform the following:
- Turn the ignition switch ON . Inspect the check engine/malfunction indicator lamp for illumination.
- The light should be lit for 5 seconds and then should go out.
- If the lamp does not illuminate, check for open circuit in the harness, blown fuse or blown bulb.