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System Operation




Anti-Lock Brake System (ABS) And Stability Control

System Operation

System Diagram





Network Message Chart

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





Module Network Input Messages - SASM (Steering Angle Sensor Module) 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) and/or wheel cylinder(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 the 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 km/h (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 BCM (Body Control Module). The BCM (Body Control Module) then sends a message to the IPC (Instrument Panel Cluster) over the MS-CAN (Medium Speed Controller Area Network) 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 evaluate rear wheel slip. Once the rear wheel slip 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. If the rear wheel slip continues and exceeds a second predetermined threshold, the ABS (Anti-Lock Brake System) module commands the HCU (Hydraulic Control Unit) to open the dump valves to decrease the rear brake pressure and allow the rear wheels to recover. 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) or wheel cylinder(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 calculates how much engine torque reduction is required to eliminate the wheel slip and sends this torque reduction message to the PCM (Powertrain Control Module) over the HS-CAN (High Speed Controller Area Network). The ABS (Anti-Lock Brake System) module also sends a traction event message to the IPC (Instrument Panel Cluster) over the HS-CAN (High Speed Controller Area Network). When the PCM (Powertrain Control Module) receives the torque reduction message, it adjusts engine timing and decreases fuel injector pulses to reduce the engine torque to the requested level. When the IPC (Instrument Panel Cluster) receives the traction event message (gatewayed through the BCM (Body Control Module) over the MS-CAN (Medium Speed Controller Area Network)), 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 stops sending the traction event and torque reduction messages. 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 km/h (62.1 mph), traction control is accomplished only through the PCM (Powertrain Control Module) torque control.
On vehicles equipped with a message center and steering wheel switches, the traction control system can be disabled by the driver through the menu in the message center, refer to the Owner's Literature. This is independent of the ABS (Anti-Lock Brake System) and ESC (Electronic Stability Control) functions, which cannot be disabled by the driver. When the driver disables the traction control function through the message center, the BCM (Body Control Module) 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 BCM (Body Control Module) which gateways the message to the IPC (Instrument Panel Cluster) over the MS-CAN (Medium Speed Controller Area Network) to illuminate the stability/traction control indicator (sliding car 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 SASM (Steering Angle Sensor Module) 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) and/or wheel cylinder(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 calculates how much engine torque reduction is required to reduce vehicle speed to help stabilize the vehicle and sends this torque reduction message to the PCM (Powertrain Control Module) over the HS-CAN (High Speed Controller Area Network). The ABS (Anti-Lock Brake System) module also sends a traction event message to the IPC (Instrument Panel Cluster) over the HS-CAN (High Speed Controller Area Network). When the PCM (Powertrain Control Module) receives the torque reduction message, it adjusts engine timing and decreases fuel injector pulses to reduce the engine torque to the requested level. When the IPC (Instrument Panel Cluster) receives this message (gatewayed through the BCM (Body Control Module) over the MS-CAN (Medium Speed Controller Area Network)), 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 stops sending the traction event and torque reduction messages. 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 SASM (Steering Angle Sensor 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 to the BCM (Body Control Module) which gateways the message to the IPC (Instrument Panel Cluster) over the MS-CAN (Medium Speed Controller Area Network) to illuminate the stability/traction control indicator (sliding car icon).

Hill Start Assist

When the vehicle is stopped on an incline greater than approximately 1.5 degrees (approximately a 3% grade), the ABS (Anti-Lock Brake System) module will hold the brake pressure for approximately 1.5 seconds while the driver transitions from the brake pedal to the accelerator pedal. This is accomplished by monitoring several HS-CAN (High Speed Controller Area Network) messages and several sensors to determine if the vehicle is stopped and not parked, and if the vehicle is on an appropriate incline. The brake pedal message sent from the PCM (Powertrain Control Module) over the HS-CAN (High Speed Controller Area Network) and the wheel speed sensor inputs allow the ABS (Anti-Lock Brake System) to determine that the vehicle has come to a complete stop. The transmission selector lever message sent by the TCM (Transmission Control Module) (on automatic transmissions) and the clutch pedal position message sent by the PCM (Powertrain Control Module) (on manual transmissions) inform the ABS (Anti-Lock Brake System) module that the vehicle is not parked. The stability sensor messages sent by the RCM (Restraints Control Module) over the private HS-CAN (High Speed Controller Area Network) enable the ABS (Anti-Lock Brake System) module to determine if the vehicle is on an incline greater than approximately 1.5 degrees (approximately a 3% grade). Once the above conditions have been met, the hill start assist function automatically engages. 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. Once the driver presses the accelerator pedal 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).

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.

Stability-Traction Control Indicator (Sliding Car Icon)

REFER to Stability-Traction Control Indicator (Sliding Car Icon) .

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

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