Circuit/System Description

Devices connected to the GMLAN serial data circuits monitor for serial data communications during normal vehicle operation. Operating information and commands are exchanged among the devices. The devices have programmed information about what messages are needed to be exchanged on the serial data circuits. The messages are also supervised and some periodic messages are used by the receiver device as an availability indication of the transmitter device.

DTC U0020 will set when fewer devices are detected on the bus before the devices can learn the other device IDs. If the communication bus is opened, or if the device power supply is lost when the vehicle is in the OFF power mode, and then placed in the RUN power mode, DTC U0020 will set in specific devices.