Circuit/System Description

WARNING: This page is about a different car, the 2009 Saturn Vue. However, it is still accessible from the selected car via links, so may be relevant.

The drive motor generator battery control module will diagnose its own systems and determine when a fault condition is present. Diagnostics and system status is communicated from the drive motor generator battery control module to the drive motor generator control module through serial data. The drive motor generator control module is the host controller for diagnostic trouble code (DTC) information.

The drive motor generator battery contains 2 high voltage (HV) contactors and a current limit relay, also called the precharge relay. The contactors 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 two contactors are a positive HV contactor, negative HV contactor, and current limit relay. These contactors close and open in a certain sequence and are controlled by the drive motor generator battery control module. The control circuit for the contactors use a buss bar attached to the circuit board and the drive motor generator battery control module supplies a ground to turn them on and off individually. The drive motor generator battery control module monitors the control circuit voltage to these contactors 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 drive motor generator battery control module detects 2 consecutive failed high voltage precharge events, a precharge wait time is activated by the drive motor generator battery control module. 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.

The power-up sequence for the HV DC system occurs in the following order:

The drive motor generator battery control module performs a precharge test, by closing both the negative and current limit relays. Because the current limit relay routes the HV current through a current limit resistor, the hybrid battery terminal voltage increases at a steady, predictable rate.
When the drive motor generator battery control module observes that hybrid battery terminal voltage and hybrid battery calculated voltage are at about the same voltage, the drive motor generator battery control module closes the positive contactor.
With both the negative and positive contactors closed, the drive motor generator battery control module opens the current limit relay.

The drive motor generator battery control module calculates a total hybrid battery voltage based upon internal hybrid battery voltage sensor. The drive motor generator battery control module measures the actual voltage at the hybrid battery terminals and compares this value to the calculated voltage.

The drive motor generator battery control module measures the actual voltage within the drive motor generator power inverter module (PIM) and compares this value to the calculated voltage. The time it takes for terminal voltage to equal hybrid battery calculated voltage is measured and recorded. If the precharge event does not occur as expected, a DTC will set.

If the drive motor generator battery control module detects 2 consecutive failed high voltage precharge events, a precharge wait time is activated by the drive motor generator battery control module. 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. The contactors will not close until the precharge wait time has timed out.