Circuit Description

When the ignition mode switch is placed in the START position, a discrete input is sent to the instrument panel module (IPM) notifying it that engine start has been requested. The IPM then verifies that the brake pedal has been depressed with a discrete input from the brake pedal position sensor and that the keyless entry transmitter, with the correct code, is in the vehicle. After this information has been verified the IPM grounds the control side of the IGN 1 relay closing the switch side of it and allowing battery positive voltage to flow from the STARTER fuse through the STARTER relay switch, ECM fuse to the battery positive voltage side of the STARTER relay coil. The IPM also sends a high speed GMLAN message to the engine control module (ECM) requesting engine start. The ECM will then verify that the internal mode switch (IMS) is in Park / Neutral. After this has been verified, the ECM grounds the control circuit of the STARTER relay closing the STARTER relay switch circuit and allowing battery positive voltage to flow through the STARTER fuse, the STATER relay switch to the S terminal of the starter solenoid cranking the engine. Ground is supplied through the engine block.