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 vehicle is equipped with a high voltage (HV) isolation monitor feature. The purpose of the HV isolation circuit is to test the resistance between the HV positive and negative direct current (DC) bus and chassis ground. The BECM only runs this test when the ignition transitions from ON to OFF the HV contactor relays have opened and the BECM is still awake. The BECM has an internal Isolation sensor that measures the resistance between the HV DC positive and negative bus and chassis ground. The BECM runs an internal self check of this sensor circuit. If the internal self check fails DTC P1AE6 will set. The BECM sends an AC signal over the DC bus and monitors its amplitude. A low amplitude or collapsed return signal indicates a loss of resistance to chassis ground and a loss of isolation will be indicated by the BECM. This DTC indicates that the fault is in the drive motor generator battery. Because this diagnostic runs after system power down, the diagnostic status does not get reported until the next key cycle.