Principles Of Operation
Anti-Lock Control - Non-Hybrid
Principles of Operation
Anti-Lock Control
The anti-lock control system is controlled by the ABS module which continuously monitors and compares the rotational speed of each wheel. The wheel speed sensors are connected to the ABS module by 2 circuits. One circuit provides voltage for sensor operation and the other circuit provides sensor input to the ABS module. As the wheels spin, the wheel speed sensor tone rings pass through the magnetic field generated by the active wheel speed sensor. This causes the strength of the magnetic field to increase (as a tooth passes the sensor) or decrease (as a gap passes the sensor) and generates a square-wave signal that is sent to the ABS module to indicate individual wheel speed.
When the ABS module detects an impending wheel lock-up, brake fluid pressure to the appropriate brake caliper or wheel cylinder will be modulated (pulsated). This is accomplished by opening and closing the appropriate solenoid valves inside the Hydraulic Control Unit (HCU) while the hydraulic pump motor is also actuated. Once the affected wheel returns to normal speed, the ABS module returns the solenoid valves to their normal position and the hydraulic pump motor is deactivated.
The ABS module is self-monitoring and will carry out self-tests at pre-determined times. When the ignition switch is turned to the RUN position, the ABS module will carry out a preliminary electrical check of the wheel speed sensors and their circuits by sending voltage through the sensor and checking for the voltage to return. When the vehicle is traveling at speeds above 20 km/h (12 mph), and the brake pedal is not being pressed, the pump motor will be commanded ON for approximately 0.5 second to check pump motor operation. Also, during all phases of operation while the vehicle is in motion, the ABS module checks for correct operation of the wheel speed sensors by comparing wheel speed input to other sensor input. If a malfunction is detected, the ABS module will deactivate the anti-lock control system and will also send a message over the High Speed Controller Area Network (HS-CAN) bus, when the Instrument Cluster (IC) receives this message it will illuminate the yellow ABS warning indicator and the stability/traction control indicator "sliding-car icon".
Electronic Brake Distribution (EBD)
The ABS incorporates a strategy called Electronic Brake Distribution (EBD). EBD uses the HCU as an electronic proportioning valve. On initial application of the brake pedal, full pressure is applied to the rear brakes. The ABS module uses wheel speed input to calculate an estimated rate of deceleration. Once vehicle deceleration exceeds a certain threshold, the ABS module closes the appropriate isolation valves in the HCU 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 and minimizes the chance of rear wheel lockup during hard braking. As the vehicle decelerates the valves are opened to increase the rear brake pressure in proportion to the front brake pressure.
Traction Control System
The traction control system is controlled by the ABS module and uses the same wheel speed sensors and tone rings that are used for the anti-lock control system. The ABS module continuously monitors and compares the rotational speed of each wheel and when it detects a wheel spinning excessively, modulates brake pressure to the appropriate brake caliper or wheel cylinder. This is accomplished by opening and closing the appropriate solenoid valves inside the HCU while the hydraulic pump motor is activated. At the same time, the ABS module sends a message over the HS-CAN bus that a traction control event is taking place. When the PCM receives this message, it will assist with traction control by adjusting engine timing and decreasing fuel injector pulses, when the IC receives this message, it will flash the stability/traction control indicator "sliding-car icon". Once the affected wheel returns to normal speed, the ABS module returns the solenoid valves in the HCU to their normal position, deactivates the hydraulic pump motor and sends another message over the HS-CAN bus indicating that the traction event has ended. The PCM returns engine timing and fuel injectors to normal operation and the IC extinguishes the stability/traction control indicator.
Once vehicle speed reaches or exceeds 100 km/h (62 mph), traction control is accomplished only through the PCM.
If the anti-lock control system is disabled due to DTCs being present in the ABS module, the traction control system will also be disabled. When the traction control system is disabled due to DTCs being present, both the ABS warning indicator and the stability/traction control indicator will be illuminated.
Electronic Stability Control (ESC) System
The Electronic Stability Control (ESC) system is controlled by the ABS module and uses the same wheel speed sensors and tone rings that are used for the anti-lock control system. The ESC system also uses input from the steering wheel rotation sensor, the stability control sensors (yaw rate, longitudinal and lateral acceleration) which are internal to the Restraints Control Module (RCM) and information from other modules sent over the HS-CAN bus to help maintain vehicle stability. The ABS module uses all of these inputs to continuously monitor the vehicle direction of travel relative to the driver's intended course. If the ABS module determines from all these inputs that the vehicle is unable to travel in the intended direction, it modulates brake pressure to the appropriate brake caliper(s) or wheel cylinder(s) by opening and closing the appropriate solenoid valves inside the HCU while the hydraulic pump motor is activated. At the same time, the ABS module sends a message over the HS-CAN bus that a stability event is taking place. When the PCM receives this message, it will assist with vehicle stability by adjusting engine timing and decreasing fuel injector pulses. When the IC receives this message, it will flash the stability/traction control indicator "sliding-car icon". Once the stability condition has been corrected, the ABS module returns the solenoid valves in the HCU to their normal position, deactivates the hydraulic pump motor and sends another message over the HS-CAN bus indicating that the event has ended. The PCM returns engine timing and fuel injectors to normal operation and the IC extinguishes the stability/traction control indicator.
If the anti-lock control system is disabled due to DTCs being present in the ABS module, the ESC system will also be disabled. When the ESC system is disabled due to DTCs being present, both the ABS warning indicator and the stability/traction control indicator will be illuminated.
Roll Stability Control (RSC(R)) System
The Roll Stability Control (RSC(R)) system is controlled by the ABS module and uses the same wheel speed sensors and tone rings that are used for the anti-lock control system. The RSC(R) system also uses input from the steering wheel rotation sensor, the stability control sensors (yaw rate, roll rate, longitudinal and lateral acceleration) which are internal to the RCM and information from other modules sent over the HS-CAN bus to help maintain vehicle stability. The ABS module uses all of these inputs to continuously monitor vehicle motion relative to the driver's intended course. If the ABS module determines from all these inputs that conditions exist for a potential roll-over event, it modulates brake pressure to the appropriate brake caliper(s) and wheel cylinder(s) by opening and closing the appropriate solenoid valves inside the HCU while the hydraulic pump motor is activated. At the same time, the ABS module sends a message over the HS-CAN bus that a stability event is taking place. When the PCM receives this message, it will assist with vehicle stability by adjusting engine timing and decreasing fuel injector pulses. When the IC receives this message, it will flash the stability/traction control indicator "sliding-car icon". Once the stability condition has been corrected, the ABS module returns the solenoid valves in the HCU to their normal position, deactivates the hydraulic pump motor and sends another message over the HS-CAN bus indicating that the event has ended. The PCM returns engine timing and fuel injectors to normal operation and the IC extinguishes the stability/traction control indicator.
If the anti-lock control system is disabled due to DTCs being present in the ABS module, the RSC(R) system will also be disabled. When the RSC(R) system is disabled due to DTCs being present, both the ABS warning indicator and the stability/traction control indicator will be illuminated.
Steering Wheel Rotation Sensor
The steering wheel rotation sensor measures the rate of rotation of the steering wheel by monitoring the steering wheel rotation ring as it passes through the sensor gap. The steering wheel rotation sensor uses the HS-CAN bus to transmit information to the ABS module about whether the steering wheel is being turned left or right and how far it is being turned. The steering wheel rotation sensor is integrated into the Electronic Power Assist Steering (EPAS) column assembly and is not serviced separately.
Stability/Traction Control Switch
The stability/traction control switch provides the driver with the ability to disable only the traction control feature. Anti-lock control, ESC and RSC(R) systems will remain functional. The switch is hard-wired to the ABS module. When the stability/traction control switch is pressed, a ground signal is sent to the ABS module. The ABS module then sends a message over the HS-CAN bus to the IC indicating that the driver has requested that the system be deactivated and the IC illuminates the stability/traction control indicator "sliding-car icon". The ABS module and the PCM will then ignore any traction events until the driver presses the switch again, the ignition key is cycled or the vehicle speed reaches or exceeds 70 km/h (43 mph). Once the vehicle speed reaches or exceeds 70 km/h (43 mph), the traction control system will re-activate but the indicator will remain illuminated.
Stability/Traction Control Indicator "Sliding-Car Icon"
Status of the traction control, ESC and RSC(R) systems is indicated by a stability/traction control indicator "sliding-car icon" located in the IC. When the driver disables the system through the use of the stability/traction control switch, this indicator will illuminate solidly. When one or more of the systems is currently active, the indicator will flash, and when the system is disabled due to DTCs being present in the ABS module, the indicator will illuminate in conjunction with the yellow ABS warning indicator.
If the systems have been disabled through the stability/traction control switch and the vehicle speed reaches or exceeds 70 km/h (43 mph), the system will activate but the indicator will remain illuminated until the driver presses the switch again or the ignition switch is cycled.
Stability/Traction Control System Sensor Calibration
When an ABS system fault has been corrected or an ABS component has been replaced, it will be necessary to calibrate the ABS module. 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.
If a DTC is logged for any component of the stability/traction control system, the DTC must be cleared or repaired before carrying out the calibration procedure except those DTCs indicating a need for calibration. The need to calibrate is also indicated by the stability/traction control indicator flashing once every 2 seconds.
To carry out the calibration procedure, connect the scan tool, proceed to the IVD Initialization sequence and follow the scan tool instructions.
ABS Module Configuration
When a new ABS module is installed it must be configured. To configure the ABS module, refer to Programmable Module Installation (PMI) in Information Bus. Programming and Relearning