Ignition Switch System

The ignition switch is used to control the ignition states, including OFF, ACC, ON and START by providing input to the BCM. This allows some systems to be activated without starting the vehicle.

The BCM also sends a message over the CAN for modules to power up or power down, depending on the ignition state determined by the BCM.

OFF 

The BCM supplies battery voltage to the ignition switch. When the ignition switch is in the OFF position, the switch is open preventing voltage output from being sent to the BCM.

ACC 

When the ignition switch is in the ACC position, the switch routes voltage through the ACC-designated circuit to the BCM. When the BCM detects voltage from the ACC-designated circuit, it activates the accessory delay relay (if equipped) (by providing ground to the coil side of the relay) and sends a message over the CAN to other vehicle modules. This allows functionality of specific electrical systems without placing additional current drain on the battery from the powertrain electrical system when the vehicle is not running.

ON 

When the ignition switch is in the ON position, the switch routes voltage through the ACC-designated and ON designated circuits to the BCM. When the BCM detects voltage from the ON-designated circuit, it activates the ignition relay and the auxiliary ignition relay (by providing ground to the coil side of the relays) and sends a message over the CAN to other vehicle modules.

START 

When the ignition switch is in the START position, the switch routes voltage through the ON-designated circuitry to the BCM and a separate circuit to the PCM to start the vehicle. The circuit designated for the START mode is only used for vehicle starting.

While the engine is cranking, the BCM inhibits the accessory delay relay (if equipped). After the vehicle starts, the BCM activates the accessory delay relay.

The PCM uses the ignition switch START input to determine when to activate the starter motor relay. For information on the starting system, Refer to the appropriate article for the procedure.

Ignition Key Inhibit 

On vehicles with an automatic transmission, the ignition key cylinder inhibit feature prevents the ignition lock cylinder from being rotated to the OFF position when the vehicle is not in PARK.

Battery voltage is supplied to the inhibit solenoid within the ignition switch. A switch within the selector lever (floor shifter) controls the ground side of the inhibit solenoid. When the selector lever is in PARK, the switch is open, allowing the ignition lock cylinder to rotate through all its positions. When the selector lever is moved out of PARK, the switch closes and the ignition key inhibit solenoid energizes to prevent the ignition lock cylinder and ignition switch from rotating to the OFF position. This also prevents the key from being removed from the ignition lock cylinder.