Circuit/System Description

WARNING: This page is about a different car, the 2008 GMC Yukon and 2008 Chevrolet Tahoe. However, it is still accessible from the selected car via links, so may be relevant.

The drive motor generator battery control module is also referred to as the battery energy control module (BECM). The BECM will diagnose its own systems and determine when a fault condition is present. Diagnostics and system status is communicated from the BECM to the hybrid powertrain control module (HPCM) through the Hybrid LAN communication circuit. The HPCM is the host controller for diagnostic trouble code (DTC) information.

The HPCM controls the operation of the high voltage (HV) contactor relays through communication with the BECM. The HPCM utilizes a pulse width modulated (PWM) contactor system request circuit and a redundant GM LAN message to command the HV contactor relays Open and Closed. Under normal operating conditions, the BECM opens and closes the HV contactor relays based only upon the HPCM command. This diagnostic identifies when the BECM has opened the HV contactor relays when the HPCM is commanding them closed.