ABS Description and Operation: Notes

This vehicle is equipped with a Bosch ABS/EBD/TCS/VSES brake system. The electronic brake control module (EBCM) and the brake pressure modulator valve (BPMV) is serviced separately. The BPMV uses a 4 circuit configuration to control hydraulic pressure to each wheel independently.

The following vehicle performance enhancement systems are provided.

• Antilock Brake System (ABS)
• Bi-State Engine Mount (BSM)
• Electronic Brake Distribution (EBD)
• Traction Control System (TCS)
• Variable Effort Steering (VES)
• Vehicle Stability Enhancement System (VSES)

The following components are involved in the operation of the above systems.

• ABS pump motor-The ABS pump motor is part of the brake pressure modulator valve. The ABS pump motor is active during ABS, VSES and base brake power assist functions.
  • System relays-There are two system relays internal to the EBCM. The solenoid relay is energized when the ignition is ON. The ABS pump motor relay supplies a ground path to the ABS pump motor when the EBCM commands the ABS pump motor on. The system relays are non serviceable.
  • Solenoids-The solenoids are commanded ON and OFF by the EBCM to operate the appropriate valves in the brake pressure modulator valve (BPMV).
• Bi-State Engine Mounts solenoid commanded by the EBCM controls vacuum to engine mounts to dampen engine vibration at idle.
• Brake booster vacuum sensor-The Brake Booster Vacuum Sensor is a input to EBCM, and operates the ABS pump motor to precharge the brake system.
• Variable Effort Steering solenoid commanded by the EBCM to control steering effort based on speed of vehicle.
• The BPMV contains the following components:
  • ABS pump motor and pump
  • Four inlet valves
  • Four outlet valves
  • Two TC isolation valves
  • Two TC supply valves
  • A master cylinder pressure sensor
  • A front low-pressure accumulator
  • A rear low-pressure accumulator
• Lateral accelerometer-The EBCM uses the lateral accelerometer to determine the sideways acceleration of the vehicle. The lateral accelerometer is packaged with the yaw rate sensor as a single component.
• Master cylinder pressure sensor-The master cylinder pressure sensor is located within the BPMV. The master cylinder pressure sensor uses a 5-volt reference and generates an output signal proportionate to the hydraulic fluid pressure which is present in the front brake circuit at the master cylinder.
• Steering wheel position sensor--The EBCM receives CAN message inputs from the steering wheel position sensor.
• Traction control switch-VSES and the engine torque reduction function of TCS are manually disabled or enabled by pressing the traction control switch.
• Wheel speed sensors (WSS)-EBCM sends a 12-volt reference voltage signal to each wheel speed sensor. As the wheel spins, the wheel speed sensor produces a square wave DC signal voltage. The wheel speed sensor increases the signal frequency as the wheel speed increases, but does not increase the signal amplitude.
• Yaw rate sensor-The EBCM uses the yaw rate sensor to determine the rate of rotation along the vehicle's vertical axis. The yaw rate sensor is packaged with the lateral accelerometer as a single component.