Turn Signals - Incandescent Rear Lamps

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 SCCM monitors the LH steering column multifunction switch position. When the LH steering column multifunction switch is in the left or right turn position, the SCCM sends a message over the HS-CAN2 to the GWM then the GWM sends the message to the BCM over the HS-CAN1 indicating a request for the LH or RH turn signal.

For vehicles without a bed, when the BCM receives a request for a turn signal, the BCM supplies on/off voltage to the appropriate turn lamps. The BCM sends a turn indicator command message over the MS-CAN to the door modules for the exterior mirror turn lamps.

For vehicles with a bed, when the BCM receives a request for a turn signal, the BCM supplies on/off voltage to the front turn lamps and the upper rear lamp bulbs stop/turn circuit and sends a message to activate the lower rear lamp stop/turn bulbs 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 upper rear lamp bulbs stop/turn circuit. The BCM also sends a turn indicator command message through the HS-CAN1 to the GWM. The GWM then sends this message through the MS-CAN to the door modules for the exterior mirror turn lamps.

The timed on/off cycle for turn lamps is determined by the BCM and is set to flash approximately 70 times per minute if both the front and rear turn signal lamps operate correctly.

If a front or rear turn signal lamp is inoperative, the BCM fast flashes the remaining turn lamp(s) approximately 150 times per minute to indicate a bulb outage to the driver.

The LH steering column multifunction switch has 2 detents for the left turn position and 2 detents for the right turn position. When placed in the first detent and released, the corresponding turn signals flash 3 times and turn off. When the LH steering column multifunction switch is moved to the second detent, the turn signal flashes until the steering wheel is turned in the opposite direction and the clockspring (vehicles without adaptive steering) or SCCM (vehicles with adaptive steering) mechanically returns the LH steering column multifunction switch to the neutral position and cancels the turn signal.

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