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

PURPOSE
The Powertrain Control Module (PCM) receives its power supply from the Constant Control Relay Module (CCRM). The CCRM is an integrated control module composed of multiple relays which also supply power to the A/C clutch, electric cooling fan, and fuel pump.

OPERATION
The CCRM receives battery voltage directly from the ignition switch when the switch is placed in RUN or START. The normally open PCM power relay (internal to CCRM) then energizes and supplies power to PCM and its outputs. A diode in line with the PCM power relay prevents damage resulting from reverse polarity.