Hydraulic Control Unit (HCU)

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 HCU contains the solenoid valves, the hydraulic pump motor and the pressure sensor used by the ABS for the various stability control systems. The ABS module and the HCU are attached directly together. A new HCU also comes equipped with a new ABS module.

Stability Control Sensors

The stability control sensors for the stability control system consist of the yaw rate sensor, roll rate sensor, lateral accelerometer and longitudinal accelerometer. The sensors are housed in the RCM which sends sensor information to the ABS module over a private HS-CAN. If any of the sensors are inoperative, a new RCM must be installed.

The yaw rate sensor measures the yaw angle which is the difference between the direction the vehicle is pointing when cornering and the direction the vehicle is actually moving.
The longitudinal accelerometer measures the acceleration and deceleration of the vehicle as it moves forward and backward.
The lateral accelerometer measures the force created when a vehicle corners that tends to push a vehicle sideways.
The roll rate sensor measures the rate of rotation of the vehicle along the centerline of the vehicle from front to back.

Lateral acceleration has 2 forms. The first is the centrifugal acceleration generated when the vehicle travels around in a circle. The second is the acceleration due to gravity. On level ground there is no lateral acceleration due to gravity. However, if the vehicle is parked sideways on a bank or incline, the sensor measures some lateral acceleration due to gravity, even though the vehicle is not moving.