Circuit/System Description

WARNING: This page is about a different car, the 2022 Cadillac CT4. However, it is still accessible from the selected car via links, so may be relevant.

The devices connected to the CAN 2 serial data circuits (4978 & 4979) monitor for serial data communications during normal vehicle operation. The serial data is transmitted on two twisted wires that allow speeds up to 2 Mbit/s. The twisted pair is terminated with two 120 Ω resistors, one is internal to the K20 Engine Control Module (ECM) and the other can be a separate resistor in a connector assembly or in another device. The resistors are used as the load for the CAN 2 bus during normal vehicle operation. The CAN 2 bus is a differential bus. The CAN 2 serial data (+) and CAN 2 serial data (-) circuits are driven to opposite extremes from a rest or idle level of approximately 2.5 V. Driving the lines to their extremes, adds 1 V to the CAN 2 serial data (+) circuit and subtracts 1 V from the CAN 2 serial data (-) circuit. If serial data is lost, devices will set a no communication code against the non-communicating device. Note that a loss of serial data DTC does not represent a failure of the device that set it.