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.