Component Description

Anti-Lock Brake System (ABS) Module 

The ABS module is attached directly to the HCU and is the electronic control unit for the ABS and stability control systems. The module monitors all sensor inputs and all HS-CAN messages that relate to ABS and stability control, and then directly controls the solenoid valves and the hydraulic pump motor in the HCU. The ABS module and HCU are serviced as an assembly. When a new ABS and HCU 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 (or initialized). 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.

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. The ABS module and the HCU are serviced as an assembly.

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 a private HS-CAN. 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.

Steering Wheel Rotation Sensor 

The steering wheel rotation sensor uses 2 optical sensors and a slotted wheel to measure the steering wheel rotation angle, speed and direction of rotation. The sensor is located inside the SASM and is serviced with the module.

Steering Angle Sensor Module (SASM) 

The SASM transmits steering wheel position, direction and speed of rotation information on the HS-CAN. The module is self monitoring and capable of setting Diagnostic Trouble Codes (DTCs). The SASM is also self calibrating and learns the straight-ahead position of the vehicle as it is driven. When a new SASM is installed, the vehicle configuration information is automatically transmitted from the BCM when the ignition is set to ON.

Traction Control Switch - Vehicles Without Steering Wheel Switches 

The traction control switch is a single-pole, push-button switch hardwired to the ABS module and located in the center console. The switch is part of the center console switch pack and is serviced as an assembly.

Wheel Speed Sensor 

On vehicles not equipped with active park assist, all 4 wheel speed sensors are active (magneto resistive) sensors that operate on the Hall-effect principle to generate a square wave signal that is proportional to the rotational speed of the wheel. Because these are active sensors, receiving voltage from the ABS module and then 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.

On vehicles equipped with active park assist, both rear  wheel speed sensors are active, bi-directional sensors. Each of the 2 sensors contain 2 sensing elements mounted side-by-side. Because the 2 sensing elements are mounted next to each other the 2 voltage signals are slightly out of phase, which causes one element to generate a voltage signal before the other element. This allows the ABS module to not only determine wheel speed, but also wheel direction for active park assist.

Wheel Speed Sensor Encoders 

The wheel speed sensor encoders are several magnets arranged in a circle around one side of the wheel bearing in alternating poles. As the wheel bearing rotates the wheel speed sensor is exposed to alternating north-south magnetic fields. The encoder is part of the wheel bearing and is serviced with the wheel bearing.