Brake Pressure Modulator Valve (BPMV)
The Brake Pressure Modulator Valve (BPMV), mounted on the driver's side of the engine compartment, provides brake fluid modulation for each of the individual wheel circuits as required during Antilock braking. During the Antilock mode, the BPMV can maintain or reduce brake fluid pressure independent of the pressure generated in the master cylinder. The BPMV does not provide more pressure than is applied by the master cylinder during braking.
With the exception of the EBCM/EBTCM, the Brake Pressure Modulator Valve (BPMV) is an integral, non-serviceable component. The BPMV should never be disassembled.
The BPMV uses a four circuit configuration with a diagonal split. Individual circuits are provided for the left front and right rear wheels, and left rear and right front wheels. The diagonal circuits are hydraulically isolated so that a leak or malfunction in one circuit will allow continued braking ability on the other.
The BPMV consists of several other components which are described as follows:
Pump Motor
The BPMV contains a motor driven recirculation pump. The pump and motor are located within the BPMV and are not serviced separately.
The pump and motor serves two purposes:
| • | During ABS Reduce Pressure events, it transfers fluid from the brake calipers back to the master cylinder. |
| • | During traction control events, the pump transfers fluid to the brake calipers. |
ABS Valves
The ABS valves decrease or maintain brake fluid pressure at the individual wheel circuits. There are four Inlet, and four Outlet solenoid valves. The EBCM/EBTCM commands the valves to their correct position during an Antilock or Traction Control event. During antilock mode, the pressure in each hydraulic circuit can be held or released by activating the appropriate valves. The normal state of the Inlet valves is open, while the normal state of the Outlet valves is closed. This allows direct master cylinder pressure to the brakes during normal braking. The ABS valves are located within the BPMV and are not serviced separately.
TCS Valves
There are two TCS Valves within the BPMV if the vehicle is equipped with Traction Control System (TCS). The two TCS Valves isolate the master cylinder so the pump motor can build brake fluid pressure for the front brakes during a traction event.
Electronic Brake Traction Control Module (EBCM/EBTCM)
The EBCM/EBTCM performs the following primary functions:
| • | Detects wheel slip tendencies. |
| • | Detects wheel speed differences. |
| • | Controls the brake system while in the antilock or traction control (TCS) mode. |
| • | Monitors the system for proper electrical operation. |
The EBCM/EBTCM also controls the display of the ABS and TCS DTCs while in diagnostic mode. The EBCM/EBTCM continuously checks the speed of each wheel in order to determine if any wheel is beginning to slip. If a wheel slip tendency is detected, the EBCM/EBTCM commands the appropriate valve positions to modulate the brake fluid pressure in some or all of the hydraulic circuits. This action prevents wheel slip and provides optimum braking. The EBCM/EBTCM continues to control pressure in the individual hydraulic circuits until a slipping tendency is no longer present. The EBCM/EBTCM continuously monitors the ABS or TCS for proper operation. If an error is detected, the EBCM/EBTCM can disable the ABS or TCS and turn on the ABS, LOW TRAC, and TRAC OFF Indicators in the instrument panel (IP) and Driver Information Display.
Electronic Brake Control Relay and Pump Motor
The electronic brake control relay provides power to the solenoid valves and to the pump motor within the Brake Pressure Modulator Valve (BPMV). The electronic brake control relay is integral part of the EBCM/EBTCM and cannot be serviced separately.
The function of the EBCM/EBTCM is to monitor inputs from all related sensors, determine wheel slip tendencies, control the brake system during Antilock, Enhanced Traction Control, or Traction Control events and monitor the system for proper operation.
The EBCM/EBTCM continuously checks the speed of each wheel to determine if any wheel is beginning to slip. If a wheel slip tendency is detected, the EBCM/EBTCM commands appropriate valve positions to modulate brake fluid pressure in some or all of the hydraulic circuits to prevent wheel slip and provide optimum braking. The EBCM/EBTCM continues to control pressure in individual hydraulic circuits until a slipping tendency is no longer present. If the EBCM/EBTCM detects a system malfunction, it can disable the ABS or TCS and turn on the Antilock and/or Traction Control Indicators in the instrument cluster.
Traction Control System On/Off Switch
The Traction Control On/Off Switch (TRAC Switch) is a momentary on switch that allows the driver to turn off the TCS if equipped, for personal or diagnostic reasons by pressing and releasing the switch. When the Traction Control switch is pressed, the TCS will be disabled and the TRAC OFF indicator turns on. The switch is located in the center console or IP.
Stoplamp Switch
The Stoplamp switch is an input to the EBCM/EBTCM. The EBCM/EBTCM uses the Stoplamp switch to tell when the brake pedal is being applied so that ABS or TCS can be disabled if necessary.
Wheel Speed Sensors
A Wheel Speed Sensor (WSS) is present at each wheel. The sensors transmit wheel speed information to the EBCM/EBTCM by means of a small AC voltage. This voltage is generated by magnetic induction caused by passing a toothed sensor ring (part of the integral hub/bearing assembly) past a stationary sensor. The signal is transmitted to the EBCM/EBTCM through shielded wiring to help reduce electro-magnetic interference that can cause false or noisy WSS inputs to the EBCM/EBTCM.
Front Wheel Speed Sensor
