Circuit Description

The ignition 1 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 engine control module (ECM) supplies the ground path to the relay coil control circuit via an internal integrated circuit, called an output driver module (ODM). One ODM output control is configured to operate as a low side driver for the ignition 1 relay. The low side driver for the ignition 1 relay also incorporates a fault detection circuit, which is continuously monitored by the ECM. When the ECM commands the ODM low side driver to turn ON, the expected voltage on the relay coil control circuit should be a low voltage condition. DTC P0687 indicates a short to battery positive voltage, or ignition 1 voltage, on the ignition 1 relay coil control circuit. If the fault detection circuit measures a high voltage condition, DTC P0687 will set.