Circuit Description (Key Start)

For ignition switch power modes refer to Body Control System Description and Operation in Computer/Integrating Systems. When the ignition switch is placed in the Start position a discrete 12 volts 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)/engine control module (ECM) notifying it that CRANK has been requested. At the same time the BCM is supplying 12 volts for the IGN 1 relay closing it and supplying battery positive voltage for the crank relay coil. The PCM/ECM verifies that the transmission is in Park or Neutral. If it is, the PCM/ECM grounds the control circuit of the crank relay. When this occurs battery positive voltage is supplied through the switch side of the crank relay to the S terminal of the starter solenoid.