Component Description

WARNING: This page is about a different car, the 2015 Ford F-150. However, it is still accessible from the selected car via links, so may be relevant.

Anti-Lock Brake System (ABS) Module

The ABS module is attached directly to the HCU and is the ECU for the ABS and stability control systems. The module monitors all sensor inputs and all HS-CAN messages relating to ABS and stability control, then directly controls the solenoid valves and the hydraulic pump motor in the HCU. The ABS module can be serviced separately from the HCU. When a new ABS is installed, the module must be programmed with the current vehicle configuration information. For additional information on module programming, Refer to: Module Configuration - System Operation and Component Description .

When an ABS or stability control fault has been corrected or a new component has been installed, the ABS module must be calibrated. The calibration procedure is required for the stability control sensors to learn the zero-position of the vehicle which means the vehicle must be on a level surface and not moving. The calibration procedure (IVD Initialization) is carried out using a diagnostic scan tool.

Brake Booster Vacuum Sensor

The brake booster vacuum sensor is a piezoelectric device used by the ABS module to monitor the vacuum in the brake booster. The sensor is hardwired to the ABS module by 3 circuits. One circuit is for the 5 volt sensor supply, one circuit is for sensor ground and one circuit is for sensor output. The sensor output ranges from 0.3 volt to 4.7 volts, depending on the amount of vacuum in the booster.

Hill Descent Control Switch

The Hill Descent Control switch is a single-pole, momentary-contact switch and is part of a 2-switch pack containing the Hill Descent Control switch and the stability-traction control switch. The switch is wired directly to the IPC.

Hydraulic Control Unit (HCU)

The HCU contains the solenoid valves, the hydraulic pump motor and the pressure sensor used by the ABS for the ABS and stability control systems. While the ABS module can be serviced separately from the HCU, a new HCU comes with a new ABS module.

Stability Control Sensors

The stability control sensors for the traction control and ESC functions consist of the yaw rate sensor, lateral accelerometer, longitudinal accelerometer and roll rate sensor. The sensors are housed in the RCM which sends sensor information to the ABS module over the HS-CAN2. If any of the sensors are defective, 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 that is 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.

Stability-Traction Control Switch

The stability-traction control switch is a single-pole, momentary-contact switch and is part of a 2-switch pack containing the stability-traction control switch and the Hill Descent Control switch. The switch is wired directly to the IPC.

Wheel Speed Sensor

All 4 wheel speed sensors are active (magneto resistive) sensors that operate on the Hall-effect principle to generate a square wave signal proportional to the rotational speed of the wheel. Because these are active sensors, receiving voltage from the ABS module and sending a varying voltage back to the ABS module, they are able to detect much lower rotational speeds than passive (magnetic inductive) sensors. Each wheel speed sensor is connected to the ABS module by 2 circuits. One circuit provides voltage for sensor operation and the other circuit provides sensor input to the ABS module.

The front wheel speed sensors are integrated into the front wheel bearing and wheel hub assembly and are serviced with the bearing and hub assembly.

The rear wheel speed sensors are mounted on the axle flange at the brake dust shield and can be serviced separately.

Wheel Speed Sensor Tone Rings

The wheel speed sensor tone rings are magnetized, toothed rings used to create a Hall-effect switch when combined with the wheel speed sensor. The front wheel speed sensor tone rings are integrated into the front wheel bearing and are serviced with the front wheel bearing. The rear wheel speed sensor tone rings are pressed onto the rear wheel axle shaft and are serviced separately from the axle shaft.