Vehicle Communication

VEHICLE COMMUNICATION
The body system consists of a combination of modules that communicate over the CCD (Chrysler Collision Detection multiplex system) bus. Through the CCD bus, information about the operation of vehicle components and circuits is relayed to the appropriate module(s). Each module receives the same information about a component or circuit as the other modules do. This significantly reduces the complexity of the wiring in the vehicle and the size of the wiring harnesses.

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 to provide 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 DRB. Problems with the operation of the bus or DRB must be corrected before proceeding with diagnostic testing. If there is a problem, refer to Powertrain Management/Computers and Control Systems/Body Control Module/Testing and Inspection for diagnostic and repair procedures.

Any of the following bus failure messages may be displayed:

Short to Battery
Either or both of the bus wires are shorted to the battery potential.

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 or a specific ground may be open.

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 all modules that provide 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 DRB cannot communicate over the bus and does not know why.