Principles of Operation
Principles of OperationStandard ABS
The ABS module receives front wheel speed information directly from the front wheel speed sensors and rear wheel speed information from the PCM over the high-speed controller area network (HS-CAN) bus. The PCM receives the rear wheel speed sensor information from the transmission output shaft speed (OSS) sensor. The ABS module then processes this information, along with other sensor inputs, to determine if an ABS event is necessary. The front wheel speed sensors sense each tooth on the sensor ring as it passes through the magnetic field of the wheel speed sensor. The OSS is a Hall-effect type sensor and senses the gear teeth on the park gear as they pass through the magnetic field of the sensor.
The ABS module continuously monitors and compares the rotational speed of each front wheel and the speed of the transmission output shaft. 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 is self-monitoring. When the ignition switch is turned to the RUN position, the ABS module will do a preliminary electrical check. At approximately 20 km/h (12 mph), the pump motor is turned on for approximately 1/2 second. Any ABS malfunction will cause the module to deactivate the system and the ABS warning indicator to illuminate; however, normal power-assisted braking remains.
Electronic Brake Distribution (EBD)
The HCU is used as an electronic proportioning valve for electronic brake distribution (EBD). The HCU controls the brake fluid pressure to the rear brakes to prevent them from applying before the front brakes. If ABS is disabled due to DTCs being present in the ABS module, EBD will also be disabled. Instrument cluster failure or a missing instrument cluster message on the HS-CAN bus will also disable E13D.
Engine Only Traction Control (EOTC)
Some vehicles may be equipped with an engine only traction control (EOTC) system. In order to achieve maximum traction, the EOTC system is designed to limit wheel spin by modulating engine torque when driving on slippery or loose surfaces. Engine torque modulation is achieved by regulating fuel and spark to the cylinders. This means that the traction control system is controlled by the PCM and not the ABS module. The only function of the ABS module in an EOTC system is to provide wheel speed information to the PCM along the HS-CAN bus. The PCM uses the wheel speed information to determine when traction control is needed. The traction control system indicator in the instrument cluster will flash during a traction control event and will illuminate without flashing if the system is inoperative due to DTCs or some other concern.
The traction control system can be disabled by pressing the traction control switch. Traction control system status is indicated by the traction control OFF indicator in the switch being illuminated and the message center (if equipped) displaying Traction Control Off. The traction control system will reset and return to normal operation when the ignition switch is cycled or when the traction control switch is pressed and released a second time during the same ignition cycle.
The traction control system is contained in the PCM and is configured when the PCM is configured. Refer to Programmable Module Installation in Information Bus (Module Configuration).
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