Body Control Modules - Old Style: Description

NOTE: This article applies to "old style" "C" & "K" Series vehicles equipped with 5.7L, 6.5L and 7.4L engines. Old style pickups are not equipped with a Body Control Module (BCM). For "new style" "C" & "K" Series vehicles equipped with 4.3L, 4.8L, 5.3L and 6.0L engines, see BODY CONTROL MODULES -- SIERRA, SILVERADO, SUBURBAN, TAHOE, YUKON & YUKON XL article.

WARNING: Vehicles are equipped with Supplemental Inflatable Restraint (SIR) system. Before attempting ANY repairs involving steering column, instrument panel or related components, see SERVICE PRECAUTIONS and DISABLING & ACTIVATING AIR BAG SYSTEM in appropriate AIR BAG RESTRAINT SYSTEMS article.

Body Control Module (BCM) is designed to process various input information it receives from sensors and switches or borrows from other vehicle systems connected to class 2 serial data line. BCM evaluates this information and controls certain body systems by commanding an output on or off.

BCM can also command other vehicle systems to control functions by sending specific messages over class 2 serial data line. BCM controls operation of audible warnings, indicator warnings, power door locks, remote keyless entry, Passlock(tm) theft deterrent, content theft deterrent, interior and exterior illumination.

BCM goes into low power mode (asleep state) when ignition has been turned off and 20 minutes have elapsed without any wake up signals. BCM goes into high power mode (wake up state) after receiving any wake up signals.

The class 2 serial data line allows communication between modules and scan tool. Modules on the class 2 serial data line are:

Body Control Module (BCM).
Instrument Panel Cluster (IPC).
Transfer Case Control Module (TCCM).
Powertrain Control Module (PCM)/Vehicle Control Module (VCM).
Supplemental Inflatable Restraint (SIR) Module.
Electronic Brake Control Module (EBCM).