The hybrid system monitors several high voltage components for attempted access. Additionally, a minimum amount of isolation resistance is maintained at all times between both negative and positive poles of the hybrid battery and the vehicle chassis. The drive motor generator power inverter module (PIM) microprocessors and the battery energy control module (BECM) monitor the hybrid system for access and loss of isolation detection.

The HVIC is a wire loop that passes through certain high voltage components. The HVIC is used to determine if access to high voltage components is being attempted. The opening of these high voltage components causes the HVIC to open. The hybrid system may react to the loss of HVIC continuity by opening the high voltage contactor relays and discharging the high voltage capacitors. The HVIC signal is generated by the BECM. The HVIC status is monitored by each motor control module (MCM) as well as the hybrid powertrain control module (HPCM) and the BECM.

The hybrid system monitors the electrical potential between high voltage and the vehicle chassis. High voltage should always be isolated from the vehicle chassis by a certain amount of resistance to avoid the potential for a life threatening current path. In the event that a high voltage leak path is detected to the vehicle chassis, the hybrid system will set a diagnostic trouble code (DTC). High voltage DC chassis isolation is monitored by both the MCMs and the BECM.

Testing for isolation requires special tools and procedures. Because of the high voltages present in the hybrid system, a loss of isolation may occur due to insulation breakdown. Insulation breakdown typically occurs only when high voltages and/or current is present. Conditions such as insulation breakdown cannot be diagnosed with a typical DMM because high voltage is not used by the DMM when measuring resistance.