Circuit Description

Modules connected to the class 2 serial data circuit monitor for serial data communications during normal vehicle operation. Operating information and commands are exchanged among the modules. When a module receives a message for a critical operating parameter, the module records the identification number of the module which sent the message for State of Health monitoring. A critical operating parameter is one which, when not received, requires that the module use a default value for that parameter. When a module does not associate an identification number with at least one critical parameter within 5 seconds of beginning serial data communication, DTC U1000 is set. When more than one critical parameter does not have an identification number associated with it, the DTC will only be reported once.

The class 2 serial data line on this vehicle is a star configuration. The following modules communicate on the class 2 serial data line:

• The body control module (BCM)
• The communication interface module (OnStar®), w/UE1
• The digital radio receiver (DRR), w/U2K
• The driver door module (DDM)
• The driver seat module (DSM), w/AAB
• The DVD player
• The electronic brake control module (EBCM)
• The engine control module (ECM), w/5.3L
• The HVAC control module
• The HVAC control module - rear auxiliary
• The inflatable restraint sensing and diagnostic module (SDM)
• The instrument panel cluster (IPC)
• The liftgate control module (LGM)
• The passenger door module (PDM)
• The powertrain control module (PCM), w/4.2L
• The radio
• The transfer case shift control module (TCSCM), w/4WD
• The theft deterrent control module (VTD), w/BAE