RAM 1500 Truck 4WD V8-5.9L VIN Z (2002)
Body Control Module: Description and Operation
Audio System
AUDIO SYSTEM
The factory installed radio receiver communicates on the Programmable Communication Interface (PCI) data bus network. The PCI Bus inputs into the
radio are used for VF dimming and remote steering wheel controls. All the radios are capable of displaying faults and allowing certain actuation tests
through the use of the DRB III. When attempting to perform PCI Bus diagnostics, the first step is to identify the radio in use in the vehicle.
When trouble shooting 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.
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.
Remote Radio Controls
These radios can be controlled via remote radio switches (optional). These switches are located on the back side of the steering wheel. They control
mode, preset, seek up, seek down, volume up and volume down functions.
These functions are inputs to the Instrument Cluster (MIC) and can be read with the DRB III. The switches are a multiplexed signal to the MIC. The
radio control MUX circuit is a 5 volt line that is pulled to ground through different value resistors built into the switches. This causes a voltage drop to
be seen by the MIC and it sends a specific message to the radio on the PCI Bus circuit. The radio then responses to the message.
This circuit is fairly simple to troubleshoot. The circuit must be complete from the switches in the steering wheel to the MIC. The ground must be
complete so that the switches can cause the voltage drop for the MIC to see. The circuit passes through the clockspring so continuity through this devise
must be verified.
Amplifier (Premium System)
The Premium Audio Amplifier uses a microprocessor for audio digital signal processing (DSP) and system diagnostics. DSP provides a more accurate
and consistent match of the audio system equalization to the vehicle interior. The O2 DR Ram amplifier has six channels for superior sound quality.
The amplifier reads the VIN from the PCI bus and sets itself to match the vehicle. The amplifier will send four beeps to the vehicle speakers at ignition
ON, if it does not read the VIN correctly. A replacement amplifier may beep at the first power up, but if these beeps are heard after the first ignition ON,
the DRB III should be used to verify the amplifier is connected to the PCI bus and that the VIN on the PCI bus is correct.
The amplifier, wiring to the speakers and the speakers work independently from the radio. The amplifier's microprocessor supports several diagnostic
functions. Tests can be run from the DRB III that will help in diagnosing audio system problems. The DRB III can display fault messages when an input
or output problem to the amplifier is detected. The amplifier can detect wiring shorts and suggest which wires are likely to be shorted. The amplifier can
send test signals that can be used to verify that the amplifier, speakers, and wiring to the speakers are operating properly. The amplifier can also be used
to test if the radio is sending audio signals to it. The DRB III can be used to verify the amplifier equalization setting matches the vehicle, in case there is
a sound quality complaint. Using the DRB III audio system diagnostics can determine the nature of the problem.
Diagnostic test the Amplifier can perform through the DRB III:
Continuous Tone Test - This test will send a continuous tone to each speaker and will verify the integrity of an individual channel.
PCI Amplifier Test - This test will detect a PCI bus or checksum failure.
Input Test - This test will detect the activity on the amplifiers input channels from the radio.
Speaker Output Test - This test will detect the activity on the amplifiers output channels to the speakers.
