Circuit/System Description
WARNING: This page is about a different car, the 2008 Buick LaCrosse and 2008 Buick Allure. However, it is still accessible from the selected car via links, so may be relevant.
When the ignition switch is placed in the START position, a discrete signal is supplied to the body control module (BCM) notifying it that the ignition is in the START position. The BCM then sends a message to the powertrain control module (PCM) that crank has been requested. The PCM then verifies that the transmission is in Park or Neutral. If it is, the PCM then supplies a ground to the control circuit of the CRANK relay. When this occurs, battery voltage is supplied through the switch of the CRANK relay to S terminal of the starter solenoid.