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

CIRCUIT OPERATION
When the ignition switch is in the START or RUN position, it connects battery voltage from circuit A1 to the A21 circuit. Circuit A21 powers circuit F18 through fuse 19 in the fuse block. Circuit F18 supplies battery voltage to the coil side of the Automatic Shut Down (ASD) relay. The Powertrain Control Module (PCM) supplies ground for the coil side of the relay on circuit K51. Circuit K51 connects to cavity C3 of the PCM.

When the PCM grounds the ASD relay, contacts inside the relay CLOSE and connect circuit A14 from fuse 17/18 in the Power Distribution Center (PDC) to circuit A142. Circuit A142 splices to the fuel injectors, ignition coil, and heated oxygen sensors. Circuit A142 also connects to cavity C12 of the PCM.