Controller Area Network (CAN)

The CAN data link is used by the Body Control Module (BCM), Engine Control Module (ECM) and Transaxle Control Module (TCM). The CAN link is only used for normal vehicle communication between these three control modules.

The CAN link scheme is a 500k/baud digital data communication protocol that operates only on logic 1's and logic 0's. Logic 0 is defined as the CAN high circuit at 3.5 volts and the CAN low at 1.5 volts or a differential of 2 volts across the circuits. Logic 1 is defined as the CAN high and CAN low circuits each at 2.5 volts or a differential of 0 volts across the circuits. One bit is equal to a logic 1 or logic 0. Therefore, CAN speed incorporates a high frequency of 500,000 logic 1's and logic 0's going by on the link every second. This high frequency allows the use of a fixed pulse width. Also, due to the high frequency, electromagnetic noises being produced by the link as well as link noise susceptibly characteristics are the reasons why the CAN high and CAN low wires are twisted together.

Unlike Class II, CAN link controllers have each controller ID stored in memory. If one controller is not communicating on the link, all other controllers know exactly which controller is not communicating no matter when the fault occurred.