Main Relay (Computer/Fuel System): Description and 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 supplies battery volt- age 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 51 of the PCM.

When the PCM grounds the ASD relay, contacts inside the relay close and connect circuit A14 from fuse 1 in the Power Distribution Center (PDC) to circuit A142. Circuit A142 splices to the generator field terminal, fuel injectors, ignition coil, and heated oxygen sensor. Circuit A142 also connects to cavity 57 of the PCM. This input tells the PCM that the ASD relay has energized.