ABS Description and Operation: Notes

Vehicles with RPO JL4 are equipped with an EBC 445V ABS/DRP/TCS/VSES module.

This module provides the following vehicle performance enhancement systems.

• Anti-Lock Brake System (ABS)
• Dynamic Rear Proportioning (DRP)
• Traction Control System (TCS)
• Vehicle Stability Enhancement System (VSES)

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 internal to the EBCM. The system relay is energized when the ignition is ON. The system relay supplies battery positive voltage to the valve solenoids and to the ABS pump motor. This voltage is referred to as system voltage.
  • Solenoids - The solenoids are commanded ON and OFF by the EBCM to operate the appropriate valves in the Brake Pressure Modulator Valve (BPMV).
  • Longitudinal accelerometer - The EBCM uses the longitudinal accelerometer to determine the actual straight-line acceleration of the vehicle.
• 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 isolation valves
  • Four dump valves
  • Two TC isolation valves
  • Two TC supply valves
  • A master cylinder pressure sensor
  • A front low-pressure accumulator
  • A rear low-pressure accumulator
• Wheel speed sensors (WSS) - As the wheels spin, toothed rings interrupt magnetic fields in the wheel speed sensors. This causes each wheel speed sensor to generate an AC signal. The EBCM uses these AC signals to calculate the wheel speed. Any imperfections in the toothed ring, such as a missing or damaged tooth, can cause an inaccurate WSS signal.
• Traction control switch - VSES and the engine torque reduction function of TCS are manually disabled by pressing and holding the traction control switch for at least 5 seconds. These functions can be re-enabled with a quick press and release of the TC switch.
• 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.
• 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.
• Steering wheel position sensor - The EBCM receives several inputs from the steering wheel position sensor. Three digital square wave signal inputs are wired directly to the EBCM harness connector, however, only signals A and B are used or monitored. The failure of the index pulse signal does not effect VSES function. The EBCM also monitors an analog steering wheel position sensor signal. Battery voltage is supplied to the digital portion of the steering wheel position sensor by the ignition 1 circuit. The analog portion of the steering wheel position sensor is supplied a 5-volt reference from the EBCM.
• Precharge pump motor and pump - The precharge pump assembly is used to assist the ABS pump in rapidly building hydraulic pressure needed during certain TCS or VSES events.