Trailer Sway Control

WARNING: This page is about a different car, the 2018 Ford Escape. However, it is still accessible from the selected car via links, so may be relevant.

Trailer sway is the undesirable yaw force a trailer can apply to the towing vehicle. Trailer sway control is a unique function of the stability control system using steering wheel angle information and yaw rate information to determine if a trailer sway event is taking place. This is done by using sensors to compare the steering wheel sensor messages and the yaw rate sensor messages with the actual vehicle motion. The ABS module receives the steering wheel sensor messages from the SASM and the yaw rate messages from the RCM, all messages are sent directly to the ABS module along the HS-CAN. If the ABS module determines from the inputs a trailer sway event is taking place, it modulates the brake pressure to the appropriate brake caliper(s) by opening and closing the appropriate solenoid valves inside the HCU while the hydraulic pump motor is activated. At the same time the ABS module calculates how much engine torque reduction is required to reduce vehicle speed to help stabilize the vehicle and sends this torque reduction message, along with a trailer sway event message, to the BCM and the PCM over the HS-CAN. The BCM sends the trailer sway event message to the IPC over the MS-CAN. When the PCM receives the torque reduction message, it adjusts engine timing and decreases fuel injector pulses to reduce the engine torque to the requested level. When the IPC receives the trailer sway event message, it flashes the stability-traction control indicator (sliding car icon) and displays TRAILER SWAY REDUCE SPEED in the message center.

Once the trailer sway has been corrected, the ABS module returns the solenoid valves in the HCU to their normal position, deactivates the hydraulic pump motor and stops sending the trailer sway event and torque reduction messages. The PCM returns engine timing and fuel injectors to normal operation and the IPC extinguishes the stability-traction control indicator (sliding car icon) and stops displaying the trailer sway message in the message center. Trailer sway control only activates when vehicle speed is greater than 65 km/h (40 mph). Any concern disabling RSC also disables trailer sway control.