Vehicle Network Protocols
The list below is but a few of the multiplexing systems in use today. Each system has its differences but for the most part they operate in a similar manner. We will take a brief look at each system including lab-scope waveforms of bus communications.
- Class 2
Chrysler Collision Detection
- Also called C2D
- Introduced on the 1988 Dodge Dynasty
- Transmission and body control networks
Handles a max of 13 Modules
- 12+ Scan tools
Chrysler Collision Detection, CCD, was one of the fi rst widely used vehicle-wide multiplexing protocols used in the US. Introduced in 1988 on the Dodge Dynasty and Chrysler New Yorker, CCD was originally used for transmission controller to engine controller communications and data sharing. Soon thereafter, body control functions were added to the CCD bus.
CCD Bus Communications
CCD Bias Voltage
CCD Bias Voltage Key Factors:
- Bias voltage provides power to the bus
- Bias voltage varies slightly between vehicles
- Bias supplied by one or more modules, typically by the module that “wakes-up” first
- Bias voltage must be between 1.5 volts and 3.5 volts, otherwise controllers may not be able to interpret messages
CCD Bus Termination
Besides power, the bus also needs ground. The CCD Bus Termination ground is:
- Provided through one or more 120 ohm termination resistors
- Located in one or more modules
- Bias and termination are not necessarily supplied by the same module
CCD Bias and Termination
Bias can be provided by either the BCM, PCM, ETAX, VIC or VTA. Any module can provide termination and the PCM may provide backup termination. If PCM and TCM are the only modules the TCM provides Bias and the PCM provides termination.
CCD Bus Resistance Values
Typical CCD bus resistance values:
- Single termination resistor 100-140 ohms
- Dual termination resistors 40-80 ohms
The termination resistor resistance should not be either 0 ohms or infinity. Without termination, bus voltage will be 5.0 volts on one wire and 0.0 volts on the other. CCD bus termination resistance can be measured with an ohm meter (battery disconnected) at either CCD pin at the DLC. Because the number of termination resistors can vary, an exact resistance specification is not possible. However, the resistance should not read 0 ohms (shorted) or infinity (open). Without termination, bus voltage will be 5.0 volts on one wire and 0.0 volts on the other, as opposed to the proper 2.51 volts on CCD- and 2.49 volts on CCD+.