Low Beams - Halogen Headlamps

WARNING: This page is about a different car, the 2019 Ford F-550 Super Duty, 2019 Ford F-450 Super Duty, 2019 Ford F-350 Super Duty, and 2019 Ford F-250 Super Duty. However, it is still accessible from the selected car via links, so may be relevant.

The BCM monitors the headlamp switch position by sending voltage signals on multiple circuits to the headlamp switch. There is one circuit for each headlamp switch position. At any given time, one of the signal circuits is switched to ground to indicate the headlamp switch position.

The BCM turns the parking lamps and headlamps on when the ignition is in RUN and the BCM detects a fault from the headlamp switch or wiring. This is normal behavior of the BCM when a fault has been detected with the inputs from the headlamp switch.

When the BCM reads a request for the headlamps on, it supplies voltage to the upper headlamp bulbs low beam circuit within each headlamp assembly and sends a message to activate the lower headlamp bulb low beams through the HS-CAN1 to the GWM. The GWM then sends this message through the MS-CAN to the BCMB (Auxiliary Lighting Control Module (ALCM)). When this message is received, the BCMB it supplies voltage to the lower headlamp bulbs low beam circuit within each headlamp assembly.

The BCM and BCMB also provides Field Effect Transistor (FET) protection of the low beam output circuits. When an excessive current draw is detected, the BCM disables the affected circuit driver. Refer to: Body Control Module (BCM) - System Operation and Component Description .