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