ABS Description and Operation (W JD9): 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)
• Electronic Brake Distribution (EBD)
• Power Brake Booster Solenoid Vacuum Supply
• Traction Control System (TCS)
• 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).
• Brake booster solenoid - The Power Brake Booster is solenoid operated, and applies a mechanical force to brake master cylinder push rod to aid in brake pedal effort.
• 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.
• Brake pressure modulator valve (BPMV) - The BPMV uses a 4-circuit configuration to control hydraulic pressure to each wheel independently.

  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.
• Power brake booster solenoid-Assist unit creates vacuum for the brake booster in case of a vacuum loss or low vacuum to the brake booster. The power brake booster Solenoid is active during increased brake booster assist, and base brake power assist functions.
• Steering wheel position sensor - The EBCM receives several inputs from the steering wheel position sensor. Three digital square wave signal inputs and one analog signal input are wired directly to the EBCM harness connector. The EBCM uses the signals signals A and B for determining position movement and uses the analog and index signals to determine absolute center. All signals are monitored for plausibility to each other. The sensor is provided ground and 5-volt power directly from the EBCM.
• 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.