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Communication

COMMUNICATION
The Programmable Communication Interface or PCI Bus is a single wire multiplexed network capable of supporting binary encoded messages shared between multiple modules. The PCI bus circuit is identified as D25. Additional tracer colors may be added to the violet in order to distinguish between different module connections. The modules are wired in parallel. Connections are made in the harness using splices.

The following modules are used on this vehicle:
- Front Control Module
- Airbag Control Module
- Left Side Impact Airbag Control Module
- Right Side Impact Airbag Control Module
- Controller Antilock Brake
- A/C Heater Control Module
- Powertrain Control Module (gas and diesel)
- Engine Control Module (diesel only)
- Radio
- Amplifier (if equipped)
- Transmission Control Module
- Transfer Case Control Module (if equipped)
- Sentry Key Immobilizer Module
- Compass Mini-Trip Computer (if equipped)
- Electro/Mechanical Instrument Cluster

Each module provides its own bias and termination in order to transmit and receive messages. The bus voltage is at 0 volts when no modules are transmitting and is pulled up to about 7 1/2 volts when modules are transmitting.





The bus messages are transmitted at a rate averaging 10800 bits per second. Since there is only voltage present when the modules transmit and the message length is only about 500 milliseconds, it is ineffective to try and measure the bus activity with a conventional voltmeter. The preferred method is to use the DRBIII lab scope. The 12 V square wave selection on the 20 volt scale provides a good view of the bus activity. Voltage on the bus should pulse between 0 and about 7 1/2 volts. Refer to the diagram for some typical displays.

The PCI Bus failure modes are broken down into two categories. Complete PCI Bus Communication Failure and individual module no response. Causes of a complete PCI Bus Communication Failure include a short to ground or battery on the PCI circuit. Individual module no response can be caused by an open PCI circuit at the module, or an open battery or ground circuit to the affected module.

Symptoms of a complete PCI Bus Communication Failure would include but are not limited to:
- All gauges on the EMIC stay at zero
- All telltales on EMIC illuminate
- EMIC backlighting at full intensity
- Dashed lines in the overhead console ambient temperature display
- No response received from any module on the PCI bus (except the ECM/PCM)
- No start (if equipped with Sentry Key Immobilizer)

Symptoms of Individual module failure could include any one or more of the above. The difference would be that at least one or more modules would respond to the DRBIII.

Diagnosis starts with symptom identification. If a complete PCI Bus Communication Failure is suspected, begin by identifying which modules the vehicle is equipped with and then attempt to get a response from the modules with the DRBIII. If any modules are responding, the failure is not related to the total bus, but can be caused by one or more modules PCI circuit or power supply and ground circuits. The DRBIII may display "BUS + SIGNAL OPEN" or "NO RESPONSE" to indicate a communication problem. These same messages will be displayed if the vehicle is not equipped with that particular module. The CCD error message is a default message used by the DRBIII and in no way indicates whether or not the PCI bus is operational. The message is only an indication that a module is either not responding or the vehicle is not equipped.


NOTE:
- The 2003 DR will have different controller configurations based on the engine, transmission and electronic throttle control combinations. You will need to identify which controller is being used on the vehicle that requires service. The 3.7L engine will use a JTEC Powertrain controller with a Transmission Control module. The 5.7L engine will use a new NGCII Powertrain controller (PCM) with EATX Transmission controller.
- The NGCII controller is not the same as the NGCI controller. The NGCI controller combines the engine and transmission controls into a single module and is used on the 4.7L engine. The NGCII controller will incorporate the engine and electronic throttle controls into a single module, the transmission functions will be controlled by a separate Transmission Control Module.

NGC Controller
Some of the changes you will see are several new Diagnostics Trouble Codes and supporting diagnostic procedures which reflect the new combined module technology. The PCM will have four color coded connectors, C1 through C4, (C1-BLK, C2-GRAY, C3-WHITE, C4-GREEN), each PCM connector will have 38 pins. Two new tools are used for probing and repairing the new PCM connectors. The Terminal Remover Miller Tool # 3638, and Diagnostic Pinout box Miller Tool # 8815. Miller Tool # 3638 is designed to release the terminals from the PCM harness connectors. You must use the Miller tool # 3638 to release the harness connector terminals or harness connector or terminal damage will occur. Miller tool # 8815 was designed for probing the PCM harness connectors. You must use Miller tool # 8815 for probing the PCM terminals or damage to the terminal will occur resulting in a poor terminal to pin connection. There are also new Verification tests and module replacement procedures for the PCM.
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