System Description

The factory installed radio receiver communicates on the Programmable Communication Interface (PCI) data bus network through a separate two-way wire harness connector. This is used for the remote radio switches that are mounted to the steering wheel, and also used for radio diagnosis with the DRB III.

The remote radio switches are resistor multiplexed units that are hard wired to the CTM through the clockspring. The CTM monitors the status of the remote radio switches and sends the proper switch status messages on the PCI data bus network to the radio receiver. The electronic circuitry within the radio is programmed to respond to these remote radio switch status messages by adjusting the radio settings as requested.

When troubleshooting output shorts or "output" error messages, the following applies:

On radios without an external amplifier, the term "output" refers to the path between the radio and the speaker. This type of circuit can be monitored all the way through the speaker connections by the radio assembly. When the radio displays a shorted output DTC with this type of system, the speaker, radio or wiring could be at fault. The output DTC could refer to a front or rear output or a left or right output. The reason for the difference is the pairing of the output sections of the radio. Some are paired left and right, others are paired front and rear.

On radios with an external amplifier, the term "output" refers to the circuit between the radio connector and the amplifier. The radio is capable of monitoring only this portion and can tell nothing about the circuit between the amplifier and the speakers. Consequently, a shorted output DTC on this type of system would only refer to this circuit. A faulty speaker could not cause this DTC.