Component Description

Anti-Lock Brake System (ABS) And Stability Control

Component Description

Anti-Lock Brake System (ABS) Module

The ABS (Anti-Lock Brake System) module is attached directly to the HCU (Hydraulic Control Unit) and is the ECU (Electronic Control Unit) for all of the vehicle dynamic systems. The module monitors all sensor inputs and all HS-CAN (High Speed Controller Area Network) messages that relate to vehicle dynamics and then directly controls the solenoid valves and the hydraulic pump motor in the HCU (Hydraulic Control Unit).
The ABS (Anti-Lock Brake System) module and HCU (Hydraulic Control Unit) are serviced as an assembly. When a new ABS (Anti-Lock Brake System)/ HCU (Hydraulic Control Unit) is installed, the module must be programmed with the vehicle information. REFER to Programmable Module Installation (PMI) .
When a vehicle dynamic system fault has been corrected or a new component has been installed, the ABS (Anti-Lock Brake System) 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 must not be moving. The calibration procedure (IVD Initialization) is carried out using the scan tool.

Hydraulic Control Unit (HCU)

The HCU (Hydraulic Control Unit) contains the solenoid valves, the hydraulic pump motor and the pressure sensor used by the ABS (Anti-Lock Brake System) for the various vehicle dynamic systems. The ABS (Anti-Lock Brake System) module and the HCU (Hydraulic Control Unit) are attached directly together and are 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 (Anti-Lock Brake System) module and then sending a varying voltage back to the ABS (Anti-Lock Brake System) module, they are able to detect much lower rotational speeds than passive (magnetic inductive) sensors. Each wheel speed sensor is connected to the ABS (Anti-Lock Brake System) module by 2 circuits. One circuit provides voltage for sensor operation and the other circuit provides sensor input to the ABS (Anti-Lock Brake System) 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 (Anti-Lock Brake System) module to not only determine wheel speed, but also wheel direction for active park assist.

Wheel Speed Sensor Magnetic Strips

The wheel speed sensor magnetic strips are made up of many magnets arranged in a circle around one side of the wheel bearing in alternating poles, so as the bearing rotates the wheel speed sensor is exposed to alternating north-south magnetic fields. The magnetic strip is located on the side of the wheel bearing facing the vehicle and is part of the wheel bearing and, as such, is serviced with the bearing.

Stability Control Sensors

The stability control sensors for the vehicle dynamic system consist of the yaw rate sensor, lateral accelerometer and longitudinal accelerometer. The sensors are housed in the RCM (Restraints Control Module) which sends sensor information to the ABS (Anti-Lock Brake System) module over a private HS-CAN (High Speed Controller Area Network). If any of the sensors are defective, a new RCM (Restraints Control Module) 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.

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 (Steering Angle Sensor Module) and is serviced with the module.

Steering Angle Sensor Module (SASM)

The SASM (Steering Angle Sensor Module) transmits steering wheel position, direction and speed of rotation information on the HS-CAN (High Speed Controller Area Network). The module is self monitoring and capable of setting DTCs (Diagnostic Trouble Codes).
The SASM (Steering Angle Sensor Module) is self calibrating and will learn the vehicle "straight-ahead position" as it is driven. However, when a new SASM (Steering Angle Sensor Module) is installed, the module must be programmed with the correct vehicle information. REFER to Programmable Module Installation (PMI) .