CCD Bus

PURPOSE
Communication over the Chrysler Collision Detection multiplex system (CCD bus) is essential to the proper operation of vehicle on-board diagnostic systems and scan tool interface. Problems with the operation of the bus must be corrected before proceeding with diagnostic testing.

OPERATION
1. The bus is a twisted pair of wires that receives and delivers coded information between control 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 is used to determine which one has higher priority and is allowed to access the bus first.

2. The twisted pair of wires 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 is the circuitry required to complete the voltage divider network and also provide some electromagnetic protection for the bus.

CIRCUIT DESCRIPTION
Circuits D1 and D2 connect the Powertrain Control Module (PCM) to the CCD Bus. Circuit D1 connects to cavity 26 of the PCM. Circuit D2 connects to cavity 46 of the PCM. Circuits D1 and D2 are a twisted pair of wires.

Both circuits D1 and D2 connect to the second data link connector located behind left from side of the center console.

The overhead console connects to the CCD bus on circuits D1 and D2. Circuits D1 and D2 are a twisted pair of wires.