Grand Cherokee 2WD Limited V8-4.7L (2002)
all airbags while performing the following inspection. If no obvious problems are found, erase stored codes, and with the ignition ON wiggle the
wire harness and connectors, rotate the steering wheel from stop to stop. Recheck for codes periodically as you work through the system. This
procedure may uncover a malfunction that is difficult to locate.
AUDIO SYSTEM
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 Body Control Module and can be read with the DRB III. The switches are a multiplexed signal to the BCM. 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 BCM 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 BCM. The ground must be
complete so that the switches can cause the voltage drop for the BCM to see. The circuit passes through the clockspring so continuity through this
devise must be verified.
CD Changer
The CD Changer is mounted in the cargo area of the passenger compartment on the right rear quarter panel. The CD Changer features a removable
10-CD magazine. The CD Changer receives both ground and radio switch power through the radio. The controls on the radio operate the CD
Changer through messages sent over the PCI Bus. The two-channel audio outputs of the CD Changer are hard-wired back to the radio, which then
outputs the signal through the channels to the speakers or amplifiers.
Part 2A
HEATING & A/C SYSTEM
System Availability
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Depending on the model, either a Manual Temperature Control (MTC) or Automatic Zone Control (AZC) HVAC system is available in these
vehicles.
System Controls
Manual Temperature Control (MTC)
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Refer to the Service Manual for MTC system description and operation information.
The Automatic Zone Control (AZC) Module:
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is fully addressable with the DRB III.
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communicates over the Programmable Communication Interface Multiplex System (PCI) Bus.
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has dual infrared sensors, mounted in the AZC module face, which independently measure surface temperature to maintain occupant comfort
levels.
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has dual-zone temperature-controls to provide a wide side-to-side variation in temperature to meet the needs of either front seat occupant.
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can be operated in a manual mode.
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uses engine temperature data, received over the PCI Bus, for cold engine blower lock-out.
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uses engine RPM data, received over the PCI Bus, for wide-open throttle A/C cut-out.
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uses vehicle speed data, received over the PCI Bus, to determine air-flow over the condenser for optimum cooling performance.
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uses Evaporator Temperature Sensor data, received over the PCI Bus, to prevent evaporator freeze up while maintaining optimum cooling
performance.
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uses Ambient Temperature Sensor data, received over the PCI Bus, to optimize comfort control.
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provides an A/C request to the BCM when compressor operation is desired.
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controls rear defogger operation.
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controls fan speed, providing 10 blower speeds in manual mode and infinite speeds in automatic mode.
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The Blower Motor Controller provides a 5.0 volt signal to the AZC Module over the Blower Motor Control circuit. The AZC Module
