Information Bus: Description and Operation
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 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 the Vehicle
Bus Failure Messages
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 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 DRB cannot communicate over the bus and does not know why.