Ignition Switch System

WARNING: This page is about a different car, the 2017 Lincoln Navigator and 2017 Ford Expedition. However, it is still accessible from the selected car via links, so may be relevant.

The BCM controls the ignition modes, including OFF, ACC, ON and START. This allows some systems to be activated without starting the vehicle.

The BCM provides voltage at all times to the ignition switch. Depending on the ignition switch position, voltage may be routed to one or two of the ignition switch input circuits back to the BCM.

OFF

The BCM supplies voltage to the ignition switch. When the ignition switch is in the OFF position, the switch is open, preventing any voltage signals from reaching the BCM. When the BCM does not detect voltage from any of the ignition mode-designated circuit, the BCM prevents voltage from being distributed to the various electrical systems.

ACC

When the ignition switch is in the ACC position, the switch routes voltage through the ACC-designated circuit to the BCM. The BCM then provides voltage to various vehicle electrical components. 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.

RUN

When the ignition switch is in the ON position, the switch routes voltage through the ACC-designated and ON-designated circuits to the BCM. The BCM then provides power to all of the vehicle electrical systems.

START

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

Ignition Key Inhibit

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 assembly 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.