ABS Description & Operation: Notes

Fig 1: Electronic Brake Control Module (EBCM)

Courtesy of GENERAL MOTORS CORP.

Fig 2: BPMV Hydraulic Flow

Courtesy of GENERAL MOTORS CORP.

This vehicle is equipped with one of the following anti-lock braking systems.

• EBC325
• EBC325S (w/NW7)
• EBC325-VSES (w/JL4)

The vehicle is equipped with the following braking enhancement systems.

• Anti-lock Brake System (ABS)
• Dynamic Rear Proportioning (DRP)
• Traction Control System (TCS) (w/NW7)
• Vehicle Stability Enhancement System (VSES) (w/JL4)

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:

  • Longitudinal accelerometer (w/JL4) - The longitudinal accelerometer is used to determine straight-line acceleration. This information is used for certain diagnostics in the Vehicle Stability Enhancement System (VSES).
  • System relay - The system relay is energized when the ignition is ON. The system relay supplies battery positive voltage to the solenoid valves and to the 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).
  • Yaw Stability Control (YSC) relay (w/JL4) - The YSC relay provides power to the charging, priming, supply, and YSC solenoids.
  • Longitudinal Accelerometer (w/JL4) - The EBCM uses the longitudinal accelerometer to determine the straight-line acceleration of the vehicle.
• Brake Pressure Modulator Valve (BPMV) - The BPMV uses a 3-circuit configuration to control the left front wheel, the right front wheel, and the combined rear wheels. The BPMV directs fluid to the left front and right front wheels independently. The BPMV directs fluid to the two rear wheels on a single hydraulic circuit.

  The BPMV contains the following components:

  • Pump motor.
  • Three isolation valves.
  • Three dump valves.
  • A front low-pressure accumulator.
  • A rear low- pressure accumulator.
  • Medium-Pressure Accumulator (MPA) Switch (w/JL4) - The medium pressure accumulator provides a mechanism for quickly applying pressure to the brakes during a yaw control event. The MPA switch monitors the status of the MPA. The MPA switch is open when the MPA is uncharged.
  • A charging valve (w/JL4).
  • A priming valve (w/JL4).
  • A supply valve (w/JL4).
  • A Yaw System Control (YSC) valve (w/JL4).

• Wheel Speed Sensors (WSS) - As the front wheels spin, toothed rings located at each wheel hub 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. The wheel speed sensors are serviceable only as part of the wheel hub and bearing assemblies. Any imperfections in the toothed ring, such as a missing or damaged tooth, can cause an inaccurate WSS signal.
• Vehicle Speed Sensor (VSS) - The input signal for rear wheel speed originates at the VSS. The Powertrain Control Module (PCM) receives rear wheel speed input from the VSS and supplies this information to the EBCM.
• Traction control switch (w/NW7) - The TCS is manually disabled or enabled using the traction control switch. The TCS can be programmed to be automatically enabled or disabled when the ignition is turned ON. The factory default is for the TCS to be automatically enabled. Refer to Programming the Traction Control Automatic Engagement Feature.
• Lateral accelerometer (w/JL4) - 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 (w/JL4) - The master cylinder pressure sensor is located on the BPMV. The master cylinder pressure sensor uses a 5-volt reference and generates an output signal between 2 % and 98 % of the reference voltage. The output signal indicates the hydraulic fluid pressure produced at the master cylinder.
• Yaw rate sensor (w/JL4) - 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 (w/JL4) - The steering wheel position input to the EBCM originates at the steering wheel position sensor. The RTD module receives steering wheel position input from the steering wheel position sensor and supplies this information to the EBCM.