Circuit Description

WARNING: This page is about a different car, the 2004 Pontiac Grand Prix. However, it is still accessible from the selected car via links, so may be relevant.

The powertrain relay is a normally open relay. The relay armature is held in the open position by spring tension. Battery positive voltage is supplied directly to the relay coil and the armature contact at all times. The powertrain control module (PCM) supplies the ground path to the relay coil control circuit via an internal integrated circuit, called an output driver module (ODM). One of the several ODM output circuits is configured to operate as a low side driver for the powertrain relay. The low side driver also incorporates a fault detection circuit, which is continuously monitored by the PCM. When the PCM commands the ODM to turn on the powertrain relay, the expected voltage on the relay coil control circuit should be a low voltage condition. If the fault detection circuit measures a high voltage condition, DTC P0685 will set. DTC P0685 indicates a short to battery positive voltage, or ignition 1 voltage on the powertrain relay coil control circuit.