Circuit Description

WARNING: This page is about a different car, the 2007 Saturn Vue. However, it is still accessible from the selected car via links, so may be relevant.

Moving the ignition switch to the START position signals the body control module (BCM) through discrete inputs from the ignition transducer that engine crank has been requested. The BCM verifies that theft is not active and sends a serial data message to the engine control module (ECM) / powertrain control module (PCM) requesting engine start. The ECM/PCM receives a 12 volt signal from the park/neutral position switch or clutch pedal start switch notifying that it is safe to start the engine. There is a splice on this circuit in the fuse block - underhood that supplies power for the starter relay coil. The starter relay coil control circuit is then grounded by the ECM/PCM closing the switch in the starter relay suppling 12 volts to the S terminal of the starter. Ground is supplied through the engine block.