Information Bus: Description and Operation

CCD BUS
Various controllers and modules exchange information through a two-wire communication port called the CCD Bus. The PCM transmits various monitored input information and control requests to other modules on the CCD Bus. The PCM also receives information and requests that effects the control of its outputs from other controllers over the CCD Bus. The CCD Bus has a measurable voltage of approximately 2.5 volts.

Various modules exchange information through a communications port called the CCD Bus. 'The Powertrain Control Module (PCM) transmits the Malfunction Indicator Lamp (Check Engine) ON/OFF signal and engine RPM on the CCD Bus. The PCM receives the Air Conditioning select input, transaxle gear position input and speed control engage inputs over the CCD Bus. The PCM also receives the air conditioning evaporator temperature signal from the CCD Bus.

The following components access or send information on the CCD Bus.
- Instrument Panel
- Body Control Module
- Air Bag System Diagnostic Module
- Full ATC Display Head
- ABS Module
- Transmission Control Module
- Powertrain Control Module
- Travel Module (if equipped)

PCI BUS
The Programmable Communication Interface Multiplex system (PCI Bus) consist of a single wire. The Body Control Module (BCM) acts as a splice to connect each module and the Data Link Connector (DLC) together. Each module is wired in parallel to the data bus through its PCI chip set and uses its ground as the bus reference. The wiring is a minimum 20 gage wire.

Various modules exchange information through a communications port called the PCI Bus. The Powertrain Control Module (PCM) transmits the Malfunction Indicator Lamp (Check Engine) ON/OFF signal and engine RPM on the PCI Bus. The PCM receives the Air Conditioning select input, transaxle gear position inputs over the PCI Bus. The PCM also receives the air conditioning evaporator temperature signal from the PCI Bus.

The following components access or send information on the PCI Bus.
- Instrument Panel
- Body Control Module
- Air Bag System Diagnostic Module
- Full ATC Display Head
- ABS Module
- Transmission Control Module
- Powertrain Control Module
- Overhead Travel Module

VEHICLE COMMUNICATION
The Chrysler Collision Detection multiplex system (CCD bus) consists of a twisted pair of wires. These wires run from one module to another. They receive and deliver coded information between the modules. The information is coded to identify the message as well as the importance of the message. When there are multiple messages trying to access the CCD bus at one time, the code determines the message that has higher priority, which is then allowed to access the bus first.

The two wires of the twisted pair that make up the CCD multiplex system are called "bus +" (bus plus) and "bus-" (bus minus) respectively. Each wire has a measurable voltage level of roughly 2.5 volts. In order to maintain the 2.5 volts on each line and provide a means of transportation for the coded messages, there is a "voltage divider network". This network consists of some modules with bias and some with termination. Bias is the part of the voltage divider network that places both bus + and bus - at 2.5 volts. Termination in the circuitry is required to complete the voltage divider network and also provides some electromagnetic protection for the bus.

NOTE: COMMUNICATION OVER THE BUS IS ESSENTIAL TO THE PROPER OPERATION OF THE VEHICLE'S ON-BOARD DIAGNOSTIC SYSTEMS AND THE DRBIII(R). PROBLEMS WITH THE OPERATION OF THE BUS OR DRBIII(R) MUST BE CORRECTED BEFORE PROCEEDING WITH DIAGNOSTIC TESTING. IF THERE IS A PROBLEM, REFER TO THE VEHICLE COMMUNICATIONS.

Bus Failure Messages

Short to Battery - Either or both of the bus wires are shorted to the battery potential or a specific ground may be open.

Short to 5 Volts - Either or both of the bus wires are shorted to a 5-volt potential.

Short to Ground - Either or both of the bus wires are shorted to ground.

Bus (+) & Bus (-) Shorted Together - The two bus wires are shorted together.

No Termination - The bus system has lost connection with all of its terminators.

Bus Bias Level Too Low - Either or both of the bus wire potentials are significantly below their normal 2.5 volts.

Bus Bias Level Too High - Either or both of the bus wire potentials are significantly above their normal 2.5 volts.

No Bus Bias - The bus system has lost connection with termination and/or bias.

Bus (+) Open - The bus (+) wire has lost connection with termination and/or bias.

Bus (-) Open - The bus (-) wire has lost connection with termination and/or bias.

Not Receiving Bus Messages Correctly - The DRBIII(R) cannot communicate over the bus and does not know why.