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 provides some electromagnetic protection for the bus.

NOTE: Communication over the bus is essential to the proper operation of the vehicle on-board diagnostic systems and the scan tool. Problems with the operation of the bus or scan tool must be corrected before proceeding with diagnostic testing. If there is a problem, refer to the Vehicle Communications section.

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 (+) & 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.