Anti-Lock Control — Traction Control and Stability Assist
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Principles of Operation
ABS with Traction Control, Electronic Stability Control (ESC) and Roll Stability Control (RSC)
The ABS module with traction control and roll stability control (RSC) manages anti-lock braking to maintain vehicle control during deceleration and performs additional functions specific to
traction control and RSC.
ABS Operation
When the ignition switch is in the RUN position, the ABS module does a preliminary electrical check and, at approximately 20 km/h (12 mph), the hydraulic pump motor is turned on for
approximately 1/2 second. During this time a buzzing or humming noise may be heard and a vibration maybe felt in the brake pedal. This is a normal condition. Any malfunction of the ABS
disables the stability assist and the ABS warning indicator illuminates. However, the power-assist braking system functions normally.
The ABS module monitors and compares the rotational speed of each wheel. Wheel speeds are measured by the wheel speed sensor, which electrically senses each tooth of the sensor
ring as it passes through the magnetic field of the sensor. When the ABS module detects an impending wheel lock, the ABS module commands the hydraulic pump motor on and
commands the hydraulic control unit (HCU) to open and close the appropriate solenoid valves to modulate the brake pressure to the individual brake caliper(s). Once the affected wheel(s)
return to the desired speed, the ABS module commands the HCU to return the solenoid valves to their normal position and normal base brake operation is restored.
The ABS module must be configured when a new ABS module is installed.
Traction Control
When the drive wheels lose traction and begin to spin, with vehicle speed under 100 km/h (62 mph), the ABS module commands the hydraulic pump motor on and commands the HCU to
open and close the appropriate solenoid valves to modulate the brake pressure to the brake caliper(s) while simultaneously sending a request to the PCM over the high-speed controller
area network (HS-CAN) bus to reduce engine torque to maintain vehicle traction. The PCM accomplishes this by minor incremental timing changes and fewer fuel injector pulses until the
ABS module ends the request. The request ends when the driven wheel speed returns to the desired speed. After the vehicle speed exceeds 100 km/h (62 mph), the traction control is
accomplished only through the PCM torque control. The traction control system can be deactivated by pressing the stability/traction control switch in the instrument panel.
When the traction control system activates, any of the following can occur:
A small deceleration or a reduction in the acceleration of the vehicle
The traction control indicator in the instrument cluster flashes
If the driver's foot is on the brake pedal, a vibration will be felt in the pedal much like ABS
Electronic Stability Control (ESC)
The electronic stability control (ESC) system constantly monitors the vehicle motion relative to the intended course. This is done by using sensors to compare the steering input and the yaw
rate sensor with that of the actual vehicle motion. The ESC system monitors information from the throttle position (TP) sensor, the steering wheel rotation sensor (steering wheel angle and
rate of change) and a yaw rate sensor (integral to the stability control sensor cluster) that measures changes in vehicle direction. If the ESC system determines from all these inputs that the
vehicle is unable to travel in the intended direction, the system adjusts the brake torque at specific wheels in response to direct measurement of the vehicle motion and reduces engine
torque to allow the vehicle to follow the intended course. The ESC system can be deactivated by pressing the stability/traction control switch in the instrument panel.
When the ESC system activates, any of the following can occur:
A rumble or grinding sound much like ABS or traction control
A small deceleration or a reduction in the acceleration of the vehicle
The roll stability control (RSC) indicator flashes
If the driver's foot is on the brake pedal, a vibration will be felt in the pedal much like ABS
Roll Stability Control (RSC)
The roll stability control (RSC) system constantly monitors the vehicle motion relative to the intended course. This is done by using sensors to compare the steering input and brake
application with that of the actual vehicle motion. The system does not activate when the vehicle is traveling in reverse; however, the standard ABS and traction control continue to function
SECTION 206-09: Vehicle Dynamic Systems
2008 E-Series Workshop Manual
DIAGNOSIS AND TESTING
Procedure revision date: 08/12/2008
Special Tool(s)
73III Automotive Meter
105-R0057 or equivalent
Flex Probe Kit
105-R025B or equivalent
Rotunda Active Wheel Speed Sensor Tester
105-R0110
Vehicle Communication Module (VCM) and Integrated Diagnostic System
(IDS) software with appropriate hardware, or equivalent scan tool
Page 1 of 6
2008 E-Series Workshop Manual
1/18/2010
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