Circuit Description

The communication among control modules is performed through the high speed GMLAN serial data bus, the low speed GMLAN serial data bus, and with RPO HP2 the high speed hybrid GMLAN serial data bus. The modules that need real time communication are attached to the high speed GMLAN busses. There are several modules that act as the gateway module or translator for communication between the various serial data busses. With RPO HP2 the serial data gateway module (SDGM) is the gateway and on all others the body control module (BCM). All high speed modules are activated by a communication enable or wakeup circuit from another module as determined by the power mode master (PMM).

Refer to Data Communication Schematics  to determine the circuit and module that activates specific high speed modules.

Signal supervision is the process of determining whether an expected signal is being received or not. Some messages are sent on a periodic basis and are interpreted as a heartbeat of a device. If such a signal is lost, the signal supervision part of the software will set a no communication DTC (U. code) against the missing device. This code is mapped on the Tech 2 screen as a code against the physical device. A lost communication DTC typically is set in modules other than the module with a communication failure.