Power is supplied at all times through the PRK BRK fuse to the relay contacts of park brake relay A and park brake relay B in the rear junction block. Power is supplied to the top of the coil on each relay when ignition is in RUN. (Refer to Power Distribution Cell 10 in Wiring Systems for the complete ignition power circuit to the relay coils.)

The rear integration module (RIM) releases the park brake by simultaneously activating two outputs. The outputs are as follows:

The RIM energizes each output by internally switching it to ground.

The RIM solenoid A control grounds CKT 1607 (PNK) which energizes the coil of park brake relay A. Relay contacts close to provide power on CKT 1628 (BLK) to energize solenoid A in the park brake release solenoid. The RIM solenoid B control grounds CKT 1605 (LT GRN/BLK ) which energizes the coil of park brake relay B. Relay contacts close to provide power on CKT 1627 (LT GRN) to energize Solenoid B in the park brake release solenoid. After two seconds, the RIM de-activates the park brake solenoid A control, de-energizing solenoid A. Solenoid B remains energized as long as the conditions are present for keeping the park brake released.

In order for the park brake release to occur, the RIM must first receive Class 2 messages verifying that the engine is running, the gear shifter is not in PARK or NEUTRAL and that the park brake switch is set. The RIM receives this message as follows. The park brake switch contacts, located within the park brake pedal assembly, stay closed as long as the park brake is set. The switch grounds CKT 1134 (LT BLU) which provides an input to the instrument cluster, signalling that the park brake is set. The cluster in turn sends a Class 2 message to the RIM informing the RIM of the switch state.

The RIM allows the park brake to be set by de-energizing solenoid B in the park brake release solenoid. (Solenoid A also must be de-energized, but this solenoid is normally energized for only a few seconds at the time that the park brake release occurs; otherwise it is de-energized.) The RIM solenoid B control opens, removing the ground from CKT 1605 (LT GRN/BLK ) which de-energizes the coil of park brake relay B. Relay contacts open, removing power from CKT 1627 (LT GRN) to de-energize Solenoid B in the park brake release solenoid.

In order for the park brake set to occur, the RIM must first receive a Class 2 message verifying that the park brake switch is released. The RIM receives this message as follows. The park brake switch contacts, located within the park brake pedal assembly, are open as long as the park brake is released. The open switch removes the ground from CKT 1134 (LT BLU), removing the input to the instrument cluster, signalling that the park brake is released. The cluster in turn sends a Class 2 message to the RIM informing the RIM of the switch state.