ABS Description and Operation (With JL4): Notes

This vehicle is equipped with a TRW EBC445 brake system. The electronic brake control module (EBCM) and the brake pressure modulator valve assembly are serviced separately. The brake pressure modulator valve assembly uses a 4 circuit configuration to control hydraulic pressure to each wheel independently.

The vehicle is equipped with the following braking systems:

• Antilock Brake System (ABS)
• Engine Drag Control (EDC)
• Dynamic Rear Proportioning (DRP)
• Traction Control System (TCS)
• Vehicle Electronic Stability (VES)

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

• Electronic brake control module (EBCM)-The EBCM controls the system functions and detects failures.

  The EBCM contains the following components:

  • System relay-The system relay is energized when the ignition is ON and no ABS DTCs are present. It supplies battery positive voltage to the solenoid valves and pump motor.
  • Vent tube-The vent tube, located in the EBCM connector, is an opening to the internal cavity of the EBCM. It allows ventilation of the EBCM internals.
• Brake pressure modulator valve (BPMV)-The BPMV contains the hydraulic valves and pump motor that are controlled electrically by the EBCM. The BPMV uses a 4 circuit configuration with a diagonal split. The BPMV directs fluid from the reservoir of the master cylinder to the left front and right rear wheels and fluid from the other reservoir to the right front and left rear wheels. The diagonal circuits are hydraulically isolated so that a leak or malfunction in one circuit will allow continued braking ability on the other.
  IMPORTANT: There is a rubber isolator located under the BPMV and on the mounting studs. The rubber isolators protect the BPMV and the EBCM from vehicle vibrations.

  The brake pressure modulator valve contains the following components:

  • Pump motor
  • Inlet valves (one per wheel)
  • Outlet valves (one per wheel)
  • Master cylinder isolation valves (one per drive wheel)
  • Prime valves (one per drive wheel)
• 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 increase the signal frequency as the wheel speed increases, but does not increase the signal amplitude.
• Traction control switch-The traction control system is manually disabled or enabled using the traction control switch.
• The EBCM uses the brake apply sensors as an indication that the brake pedal is applied.
• Lateral accelerometer sensor-The EBCM uses the lateral accelerometer sensor as an indication of the lateral acceleration of the vehicle.
• Yaw rate sensor-The EBCM uses the yaw rate sensor as an indication of the yaw rate of the vehicle.
• Steering wheel position sensor (SWPS)-The EBCM uses the SWPS as an indication of the position and rotation of the steering wheel.