Malfunction Indicator Lamp-PCM Output
MALFUNCTION INDICATOR LAMP-PCM OUTPUTFig. 12 Check Engine Lamp Typical:
The malfunction indicator lamp illuminates each time the ignition key is turned on. It will stay on for approximately three seconds as a bulb test. The lamp is displayed on the instrument panel as the CHECK ENGINE lamp (Fig. 12).
The signals needed to activate the lamp are sent from the Powertrain Control Module (PCM) to the instrument panel through the CCD bus circuits.
If the PCM receives an incorrect signal, or no signal from certain sensors or emission related systems, the lamp is turned on. This is a warning that the PCM has recorded a system or sensor malfunction. In some cases, when a problem is declared, the PCM will go into a limp-in mode. This is an attempt to keep the system operating. It signals an immediate need for service.
The lamp can also be used to display a Diagnostic Trouble Code (DTC). Refer to Computers and Control Systems/Testing and Inspection/Procedures.
The lamp is also used to display certain engine misfires. Refer to Computers and Control Systems/Testing and Inspection/Procedures.