Circuit/System Description

WARNING: This page is about a different car, the 2009 GMC Sierra and 2009 Chevrolet Silverado. However, it is still accessible from the selected car via links, so may be relevant.

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 V 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.