Main Relay (Computer/Fuel System): Description and Operation

PURPOSE
The Powertrain Control Module (PCM) power relay provides power to the PCM. The PCM power relay also provides reverse battery protection for the PCM and related actuator assemblies.

CONSTRUCTION
The relay is a single pole double throw type. This relay does not have an internal diode and is used with a separate stand alone diode.

OPERATION
The PCM power relay is energized in "RUN" or "START" through the ignition switch. When energized, battery voltage (B+) flows through the relay. This voltage powers the PCM and its outputs.

When the ignition switch is turned "OFF", the relay de-energizes, stopping B+ to the PCM.