Part 2

Anti-Lock Brake System (ABS) And Stability Control

MyKey(R) Interaction

Through the MyKey(R) feature, the traction control function of the vehicle dynamic system can be configured to be always on or to allow the driver to select the traction control function on or off.

When the traction control function is configured to be always on and a MyKey(R) restricted key is in use, the IPC (Instrument Panel Cluster) will ignore any requests made by the driver to disable the traction control function and will not send any traction control disable messages to the ABS (Anti-Lock Brake System) module. Refer to the Owner's Literature.

Terrain Management

The ABS (Anti-Lock Brake System) module adjusts the vehicle dynamic system operational parameters when the terrain mode request message is received from the ATCM (All Terrain Control Module), depending on the terrain mode requested.
- Grass/Gravel/Snow - The base ABS (Anti-Lock Brake System), traction control and ESC (Electronic Stability Control) lower the threshold used to detect wheel lock up as it is more likely to occur on loose, slippery surfaces.
- Sand - The base ABS (Anti-Lock Brake System) raises the threshold used to detect wheel lock up to allow the vehicle to "dig into" sand or deep gravel surfaces. Traction control and ESC (Electronic Stability Control) raise the parameters for brake and engine torque reductions to optimize traction and engine performance.
- Mud/Ruts - The base ABS (Anti-Lock Brake System) lowers the threshold used to detect wheel lock up as it is more likely to occur on slippery, muddy surfaces. Traction control and ESC (Electronic Stability Control) raises the parameters for brake and engine torque reductions to optimize traction and engine performance.

For additional information on the terrain management system, REFER to All-Wheel Drive (AWD) .

Hill Descent Control

When the Hill Descent Control(TM) switch is pressed, the ATCM (All Terrain Control Module) sends a message to the ABS (Anti-Lock Brake System) module requesting hill descent braking assist. Once the vehicle speed is between 5 kmh (3.1 mph) and 32 kmh (19.9 mph) and the transmission is in REVERSE or any forward gear, the ABS (Anti-Lock Brake System) module uses the hydraulic pump motor and the HCU (Hydraulic Control Unit) solenoid valves to maintain the vehicle speed set by the driver. If the vehicle speed is increased or decreased outside of the operational window, the system remains active but descent speed cannot be set or maintained.

The Hill Descent Control(TM) system requires a cool down period after sustained use. The ABS (Anti-Lock Brake System) module continually monitors the descent speed, angle of descent, pump motor run time and solenoid valve use. Once the ABS (Anti-Lock Brake System) module determines that a cool down period is needed, the ABS (Anti-Lock Brake System) module sends a message to the BCM (Body Control Module) and the IPC (Instrument Panel Cluster) over the HS-CAN (High Speed Controller Area Network) to alert the driver via a message center message that the system requires a cool down period.

Trailer Sway Control

Trailer sway control is a unique function of the vehicle dynamic system that uses steering wheel angle information from the SCCM (Steering Column Control Module) (vehicles with active park assist) or from the PSCM (Power Steering Control Module) (vehicles without active park assist) and the yaw information from the RCM (Restraints Control Module) to determine if a trailer sway event is taking place. Trailer sway is the undesirable yaw force a trailer can apply to the towing vehicle. If it is determined that an event is taking place, the ABS (Anti-Lock Brake System) module modulates brake pressure to the appropriate brake caliper(s) by opening and closing the appropriate solenoid valves inside the HCU (Hydraulic Control Unit) while the hydraulic pump motor is activated. At the same time, the ABS (Anti-Lock Brake System) module sends a message over the HS-CAN (High Speed Controller Area Network) that a trailer sway event is taking place. When the PCM (Powertrain Control Module) receives this message, it assists with trailer sway control by adjusting engine timing and decreasing fuel injector pulses. When the IPC (Instrument Panel Cluster) receives this 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 (Anti-Lock Brake System) module returns the solenoid valves in the HCU (Hydraulic Control Unit) to their normal position, deactivates the hydraulic pump motor and sends another message over the HS-CAN (High Speed Controller Area Network) bus indicating that the event has ended. The PCM (Powertrain Control Module) returns engine timing and fuel injectors to normal operation and the IPC (Instrument Panel Cluster) extinguishes the sliding car icon.

Trailer sway control only activates when vehicle speed is greater than 65 kmh (40.4 mph). Any malfunction that disables the RSC (Roll Stability Control) function of the vehicle dynamic system also disables trailer sway control. Trailer sway control can also be disabled by the driver through the menu in the message center. Regardless of the chosen state (enabled or disabled) set by the driver, trailer sway control is enabled at each ignition key cycle.

Stability-Traction Control Indicator (Sliding Car Icon)

REFER to Stability-Traction Control Indicator (Sliding Car Icon) Instrument Panel Cluster (IPC).

Stability-Traction Control Disabled Indicator (Sliding Car OFF Icon)

REFER to Stability-Traction Control Disabled Indicator (Sliding Car OFF Icon) Instrument Panel Cluster (IPC).

Curve Control

The ABS (Anti-Lock Brake System) module continuously monitors the vehicle motion relative to the intended course. This is done by using sensors to compare the steering wheel input, the yaw rate sensor input, the lateral acceleration sensor input and the longitudinal acceleration sensor input with that of the actual vehicle motion. The SCCM (Steering Column Control Module) (vehicles with active park assist) or PSCM (Power Steering Control Module) (vehicles without active park assist) sends the steering wheel angle and rate of change information to the ABS (Anti-Lock Brake System) module over the HS-CAN (High Speed Controller Area Network) while the RCM (Restraints Control Module) sends the yaw rate, lateral acceleration and longitudinal acceleration sensor information to the ABS (Anti-Lock Brake System) module over a private HS-CAN (High Speed Controller Area Network). If the ABS (Anti-Lock Brake System) module determines from the inputs that the vehicle is experiencing over-steer or under-steer, the module sends a message over the HS-CAN (High Speed Controller Area Network) that a curve control event is taking place. When the PCM (Powertrain Control Module) receives this message, it assists with curve control by adjusting engine timing and decreasing fuel injector pulses. When the IPC (Instrument Panel Cluster) receives this message, it flashes the stability/traction control indicator (sliding car icon). The ABS (Anti-Lock Brake System) module continues to monitor the sensor inputs while the PCM (Powertrain Control Module) assists with curve control. If the ABS (Anti-Lock Brake System) module determines that PCM (Powertrain Control Module) intervention is insufficient to control the stability event, the ABS (Anti-Lock Brake System) module modulates brake pressure to the appropriate brake caliper(s) by opening and closing the appropriate solenoid valves inside the HCU (Hydraulic Control Unit) while the hydraulic pump motor is activated. Once the vehicle instability has been corrected, the ABS (Anti-Lock Brake System) module returns the solenoid valves in the HCU (Hydraulic Control Unit) to their normal position, deactivates the hydraulic pump motor and sends another message over the HS-CAN (High Speed Controller Area Network) bus indicating that the event has ended. The PCM (Powertrain Control Module) returns engine timing and fuel injectors to normal operation and the IPC (Instrument Panel Cluster) extinguishes the sliding car icon.

The Curve Control function does not operate with the transmission in REVERSE. The ABS (Anti-Lock Brake System) module disables the Curve Control function if there are any wheel speed sensor, stability sensor or steering angle sensor DTCs (Diagnostic Trouble Codes) present in the ABS (Anti-Lock Brake System) module. Also, if there is a communication error between the ABS (Anti-Lock Brake System) module and the PSCM (Power Steering Control Module), the SCCM (Steering Column Control Module) or the RCM (Restraints Control Module) the Curve Control function is disabled. When the Curve Control function is disabled, the ABS (Anti-Lock Brake System) module sends a message over the HS-CAN (High Speed Controller Area Network) to the IPC (Instrument Panel Cluster) to illuminate both the sliding car icon and the stability/traction control disabled indicator (sliding car OFF icon).

Supplemental Braking Assist

In addition to preventing wheel lock up during braking events, the ABS (Anti-Lock Brake System) module is also able to provide supplemental hydraulic brake assist through the use of the hydraulic pump motor and the HCU (Hydraulic Control Unit). This is done in the event of a severe vacuum loss at the brake booster, to maintain the distance gap set by the adaptive cruise control system or to aid in the avoidance of forward collisions.

The ABS (Anti-Lock Brake System) module utilizes the HCU (Hydraulic Control Unit) and hydraulic pump motor to aid in bringing the vehicle to a safe, controlled stop in the event of severe vacuum loss at the brake booster. The ABS (Anti-Lock Brake System) module continually monitors the vacuum in the brake booster through the use of a vacuum sensor. When the vacuum sensor indicates vacuum is below a predetermined level, a DTC (Diagnostic Trouble Code) is set in the ABS (Anti-Lock Brake System) module. If this occurs during a braking event or if the driver attempts to stop the vehicle with a low vacuum condition in the brake booster, the ABS (Anti-Lock Brake System) module activates the hydraulic pump motor in the HCU (Hydraulic Control Unit) to assist with vehicle braking.

On vehicles equipped with adaptive cruise control, the C-CM (Cruise-Control Module) monitors the area forward of the vehicle. When an object enters this area and closes the distance gap set by the driver, the C-CM (Cruise-Control Module) sends a deceleration request to the ABS (Anti-Lock Brake System) module over the HS-CAN (High Speed Controller Area Network) (either an adaptive cruise control deceleration request or a collision avoidance deceleration request). When the deceleration request message is received, the ABS (Anti-Lock Brake System) module activates the hydraulic pump motor and solenoid valves in the HCU (Hydraulic Control Unit) to slow the vehicle down to maintain the distance gap set by the driver. Once the distance gap set by the driver is achieved, the C-CM (Cruise-Control Module) stops sending the deceleration request message and the ABS (Anti-Lock Brake System) module deactivates the hydraulic pump motor and solenoid valves in the HCU (Hydraulic Control Unit). If the C-CM (Cruise-Control Module) determines that the amount of braking provided by the ABS (Anti-Lock Brake System) module is insufficient, the C-CM (Cruise-Control Module) sends a forward collision avoidance braking request message to the ABS (Anti-Lock Brake System) module and warns the driver, both audibly and visually, through the use of the HUD (Head Up Display). After receiving the braking request message, the ABS (Anti-Lock Brake System) module waits for brake pedal input and at that time applies maximum braking assist using the hydraulic pump motor and the HCU (Hydraulic Control Unit). For additional information on the adaptive cruise control system, REFER to Adaptive Cruise Control (ACC) Operation Cruise Control - Adaptive. For additional information on the collision avoidance system, REFER to Collision Avoidance Operation Collision Avoidance.

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.

On vehicles equipped with adaptive cruise control, 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) module is installed, whether with a new HCU (Hydraulic Control Unit) or not, the module must be programmed with the vehicle information. For additional information on module programming, REFER to Programmable Module Installation (PMI) Module Configuration.

When a vehicle dynamic system fault has been corrected or a component has been replaced, the ABS (Anti-Lock Brake System) module requires calibration. 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 is carried out using a 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. On vehicles equipped with adaptive cruise control, the ABS (Anti-Lock Brake System) module and HCU (Hydraulic Control Unit) 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, roll 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 inoperative, 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.
- 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

On vehicles not equipped with active park assist, the steering wheel rotation speed and direction of travel is determined by the PSCM (Power Steering Control Module) and is sent to the ABS (Anti-Lock Brake System) module over the HS-CAN (High Speed Controller Area Network).

On vehicles equipped with active park assist, the steering wheel rotation sensor directly measures the steering wheel rotation speed and direction of rotation. The sensor is mounted on the SCCM (Steering Column Control Module) and the information is sent to the ABS (Anti-Lock Brake System) module over the HS-CAN (High Speed Controller Area Network).

Brake Booster Vacuum Sensor

The brake booster vacuum sensor is a piezoelectric device used by the ABS (Anti-Lock Brake System) module to monitor the vacuum in the brake booster. The sensor is hardwired to the ABS (Anti-Lock Brake System) 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 0.2 volt to 4.9 volts, depending on the amount of vacuum in the booster. The sensor is located on the front of the brake booster at the 7 o'clock position and can be serviced separately from the brake booster.

All Terrain Control Module (ATCM)

The ATCM (All Terrain Control Module) houses the hill descent switch. The hill descent switch is a momentary contact switch with a LED (Light-emitting Diode) used to indicate when the system has been enabled. For additional information on the ATCM (All Terrain Control Module), REFER to All Terrain Control Module (ATCM) .