Circuit Description

The main 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 of the ODM output circuits is configured to operate as a low side driver for the main relay. The low side driver also incorporates a fault detection circuit, which is continuously monitored by the ECM.