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 hybrid drive motor generator battery contains 3 high voltage contactor relays also referred to as high voltage (HV) relays. The HV relays allow the high voltage DC batteries to be connected to the vehicle or safely contain the DC high voltage within the drive motor generator battery assembly. The three HV relays are a positive HV contactor relay, negative HV contactor relay, and current limit relay. These relays/contactors close and open in a certain sequence and are controlled by the BECM. The control circuit for the HV relays use a wire from the relay to case ground and the BECM supplies voltage to turn them on and off individually. The BECM monitors the control circuit voltage to these relays and 12 volt reference circuit internal to the control module to determine if the circuit is open by comparing the two voltage readings. If the BECM detects 2 consecutive failed high voltage precharge events, a precharge wait time is activated by the BECM. This precharge wait time limit is to allow the Precharge circuit internal to the drive motor generator battery assembly to cool down. The precharge wait time counts down in seconds and is displayed on the scan tool.