CAN Communications | Vehicle Network Protocols

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.

  • Chrysler
    1. CCD
    2. PCI
    3. SCI
  • Ford
    1. SCP
  • General Motors
    1. Class 2

Chrysler CCD

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.

Chrystler CCD Wiring Diagram

CCD Bus Communications

Chrystler CCD Bus Communication Voltage Chart

The CCD bus consists of two wires: CCD+ and CCD-. CCD+ is typically violet in color and CCD- is typically white. The two wires will always be twisted together, one turn every 1.75”.

CCD Bias Voltage

CCD Bias Voltage Waveform

When the lab scope is connected to CCD+ and ground, we see the bias voltage of 2.5 volts. The lab-scope can be connected anywhere on the CCD+ circuit.

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 Bias Voltage Wiring Diagram

Bus bias voltage is provided by a 5-volt power supply through a 13K ohm resistor to CCD-. Bias voltage then passes through a 120 ohm resistor to CCD+ and then through another 13K ohm resistor to ground. The voltage drop through the termination resistor creates 2.51 volts on CCD- and 2.49 volts on CCD+. In this state, the bus is idle.

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+.

This post was written by: Martin Hand

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Martin Hand

About Martin Hand

ASE Certified L1 Advanced Mastertech. Martin Hand has over 15 years experience in Asian and European Import Auto Repair. Specializing in electrical diagnosis, engine performance, AT/MT transmission repair/rebuild. Martin is also pursuing a degree in Computers Science & Information Systems starting at Portland Community College while he plans to transfer to OIT. Certified in Java application level programming, experienced with other languages such as PHP, Ruby, JavaScript and Swift. Martin has future plans of automotive diagnostic software development.

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