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Part 1




Anti-Lock Brake System (ABS) And Stability Control

Overview

The vehicle dynamic system is comprised of the following subsystems which assist the driver in maintaining control of the vehicle:
- Base ABS (Anti-Lock Brake System)
- EBD (Electronic Brake Distribution)
- Traction Control
- ESC (Electronic Stability Control)
- RSC (Roll Stability Control)
- Curve Control
- Trailer Sway Control
- Hill Start Assist
- Hill Descent Control(TM)
- Terrain Management System
- Supports Adaptive Cruise Control
- Supports Collision Avoidance

The base ABS (Anti-Lock Brake System) helps to maintain steering control by preventing the wheels from locking up during hard braking. The base ABS (Anti-Lock Brake System) also includes a brake assist function that will provide maximum brake system pressure during a severe braking situation.

The EBD (Electronic Brake Distribution) system helps to maintain vehicle control by keeping a balanced braking condition between the front and rear wheels.

The traction control system helps to prevent loss of traction by reducing drive-wheel spin during acceleration.

The ESC (Electronic Stability Control) system helps to prevent skids or lateral slides by activating portions of the base ABS (Anti-Lock Brake System).

The RSC (Roll Stability Control) system helps to prevent excessive vehicle roll by activating portions of the base ABS (Anti-Lock Brake System).

The Curve Control system helps to maintain vehicle stability during adverse maneuvers such as cornering or avoiding objects in the roadway.

The Trailer Sway Control system helps maintain vehicle stability while towing a trailer by detecting and aiding in the reduction of conditions that cause trailer sway.

The Hill Start Assist system prevents vehicle roll back when pulling away while stopped on an incline without the use of the parking brake.

The Hill Descent Control(TM) system helps to maintain a low speed while descending steep inclines in various surface conditions.

The Terrain Management System helps to maintain vehicle traction by adapting the responses of the engine, transmission, 4WD (Four-Wheel Drive) system and the vehicle dynamic system to the demands of the terrain. For additional information on the terrain management system, REFER to All-Wheel Drive (AWD) Four Wheel Drive (4WD) Systems.

For information on the Adaptive Cruise Control system, REFER to Adaptive Cruise Control (ACC) Operation Cruise Control - Adaptive.

For information on the Collision Avoidance system, REFER to Collision Avoidance Operation Collision Avoidance.

Some noise from the system and pulsations in the brake pedal are normal conditions during most vehicle dynamic system activations. Also, longer than normal brake pedal travel may be experienced immediately following a vehicle dynamic system activation.

System Operation

System Diagram





Network Message Chart

Module Network Input Messages - ABS (Anti-Lock Brake System) Module














Base Anti-Lock Brake System (ABS) Function

The ABS (Anti-Lock Brake System) module continuously monitors brake pedal input, lateral vehicle motion and the rotational speed of each wheel. The PCM (Powertrain Control Module) sends the brake pedal switch 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 lateral acceleration sensor information to the ABS (Anti-Lock Brake System) module over a private HS-CAN (High Speed Controller Area Network). Wheel speed information is retrieved by the ABS (Anti-Lock Brake System) module using 4 active wheel speed sensors, one for each wheel. When the ABS (Anti-Lock Brake System) module detects an impending wheel lock during a braking 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 affected wheel(s) return to the desired speed, the ABS (Anti-Lock Brake System) module returns the solenoid valves in the HCU (Hydraulic Control Unit) to their normal position.

The ABS (Anti-Lock Brake System) module has 2 self-test options, one is carried out using a scan tool and the other is carried out when the ABS (Anti-Lock Brake System) is initialized (ignition ON). During either self test the ABS (Anti-Lock Brake System) module carries out a preliminary electrical check of the system sensors and activates the hydraulic pump motor for approximately one-half second. During this time, a buzzing or humming noise may be heard and a vibration may be felt in the brake pedal and is a normal condition. During the module initialized self test, the pump motor check is carried out at approximately 10 kmh (6.2 mph). Any malfunction detected in the system causes the module to set a DTC (Diagnostic Trouble Code), disable the ABS (Anti-Lock Brake System) function and send a message over the HS-CAN (High Speed Controller Area Network) to the IPC (Instrument Panel Cluster) to illuminate the ABS (Anti-Lock Brake System) warning indicator. However, the base hydraulic power-assist braking system will function normally.

Electronic Brake Distribution (EBD)

On initial application of the brake pedal, full pressure is applied to the rear brakes. The ABS (Anti-Lock Brake System) module then uses wheel speed sensor inputs to calculate an estimated rate of deceleration. Once vehicle deceleration exceeds a predetermined threshold, the ABS (Anti-Lock Brake System) module commands the HCU (Hydraulic Control Unit) to close the appropriate isolation valves to hold the rear brake pressure constant while allowing the front brake pressure to build. This creates a balanced braking condition between the front and rear wheels. As the vehicle decelerates, the valves are opened to increase the rear brake pressure in proportion to the front brake pressure. A slight bump sensation may be felt in the brake pedal when EBD (Electronic Brake Distribution) is active. If the ABS (Anti-Lock Brake System) is disabled due to DTCs (Diagnostic Trouble Codes) being present in the ABS (Anti-Lock Brake System) module, EBD (Electronic Brake Distribution) continues to function unless the DTCs (Diagnostic Trouble Codes) are for wheel speed sensors or the HCU (Hydraulic Control Unit)/solenoid valves. When EBD (Electronic Brake Distribution) is disabled, the ABS (Anti-Lock Brake System) warning indicator, the red brake warning indicator and traction control indicator illuminate.

Traction Control Function

The ABS (Anti-Lock Brake System) module continuously monitors and compares the rotational speed of the drive wheels in relation to the non-driven wheels. When the drive wheels begin to spin faster than the non-driven wheels, 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 traction event is taking place. When the PCM (Powertrain Control Module) receives this message, it assists with traction 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). Once the driven wheel speed returns to the desired speed, 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. After the vehicle speed exceeds 100 kmh (62.1 mph), traction control is accomplished only through the PCM (Powertrain Control Module) torque control.
The traction control system can be disabled by the driver through the menu in the message center by changing the TRACTION CNTRL setting in the message center from ON to OFF. This is independent of the ABS (Anti-Lock Brake System), ESC (Electronic Stability Control) and RSC (Roll Stability Control) functions, which cannot be disabled by the driver. When the driver disables the traction control function through the message center, the IPC (Instrument Panel Cluster) communicates traction control system status to the ABS (Anti-Lock Brake System) module via the HS-CAN (High Speed Controller Area Network). The ABS (Anti-Lock Brake System) module takes no further action in regards to traction control until the driver activates the function or until the ignition is cycled from OFF to ON.

The ABS (Anti-Lock Brake System) module disables the traction control function if there are any wheel speed sensor or solenoid valve DTCs (Diagnostic Trouble Codes) present in the ABS (Anti-Lock Brake System) module. The traction control function is also disabled if there is a communication error between the ABS (Anti-Lock Brake System) module and the PCM (Powertrain Control Module). When the traction control function is disabled, the ABS (Anti-Lock Brake System) module sends a message to the IPC (Instrument Panel Cluster) to illuminate the stability/traction control disabled indicator (sliding car OFF icon).

Electronic Stability Control (ESC)

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 and the yaw rate 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 yaw rate 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 unable to travel in the intended direction, 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 vehicle stability event is taking place. When the PCM (Powertrain Control Module) receives this message, it assists with vehicle 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). 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 ESC (Electronic Stability Control) function does not operate with the transmission in REVERSE. The ABS (Anti-Lock Brake System) module disables the ESC (Electronic Stability 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 ESC (Electronic Stability Control) function is disabled. When the ESC (Electronic Stability 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).

Roll Stability Control(TM)

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 wheel speed sensor input, throttle position input, steering wheel input and the roll rate 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), the PCM (Powertrain Control Module) sends the throttle position sensor information over the HS-CAN (High Speed Controller Area Network) and the RCM (Restraints Control Module) sends roll rate sensor information to the ABS (Anti-Lock Brake System) module over a private HS-CAN (High Speed Controller Area Network). The wheel speed sensor information comes directly from the ABS (Anti-Lock Brake System) wheel speed sensors.

If the ABS (Anti-Lock Brake System) module determines from the inputs that the vehicle is becoming unstable, 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 vehicle stability event is taking place. When the PCM (Powertrain Control Module) receives this message, it assists with vehicle stability 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). By adjusting brake and engine torque the system can reduce the cornering forces and, therefore, the total roll movement acting on the vehicle. 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 RSC (Roll Stability Control) function does not operate with the transmission in REVERSE. The ABS (Anti-Lock Brake System) module disables the RSC (Roll Stability 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), SCCM (Steering Column Control Module), PCM (Powertrain Control Module) or the RCM (Restraints Control Module), the RSC (Roll Stability Control) function is disabled. When the RSC (Roll Stability 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).

Hill Start Assist

The ABS (Anti-Lock Brake System) module uses the brake pedal switch message and ABS (Anti-Lock Brake System) wheel speed sensor input to determine that the vehicle is at a complete stop. The transmission selector lever message and parking brake message let the ABS (Anti-Lock Brake System) module know that the vehicle is not being parked. The stability sensor messages from the RCM (Restraints Control Module) enable the ABS (Anti-Lock Brake System) module to determine if the vehicle is on an incline greater than 5 degrees or greater than a 3% grade. The hill start assist function automatically engages once the above conditions have been met. As the driver releases the brake pedal, the ABS (Anti-Lock Brake System) module commands the HCU (Hydraulic Control Unit) to close the isolation valves which will maintain the current brake system pressure, preventing the vehicle from rolling down the incline. The ABS (Anti-Lock Brake System) will hold the brake pressure for up to 2 seconds while the driver transitions to the accelerator pedal. As the accelerator pedal is pressed and the engine RPM (Revolutions Per Minute) increases, the ABS (Anti-Lock Brake System) module gradually releases the brake pressure to make sure the vehicle is neither rolling back nor driving off until there is sufficient driving torque to accelerate the vehicle forward (or backward if reversing up the incline).
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