The Brake Pressure Modulator Valve (BPMV), mounted on the left 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 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:
The BPMV contains a motor driven recirculation pump. The pump serves two purposes: 1) During ABS Pressure Decrease events, it transfers fluid from the brake calipers back to the master cylinder; and 2) During traction control, it transfers fluid from the master cylinder to the front brake calipers. The pump and motor are located within the BPMV and are not serviced separately.
The ABS valves decrease or maintain brake fluid pressure at the individual wheel circuits. There are four inlet and four outlet solenoid valves. The solenoid valves maintain, increase, or decrease brake fluid pressure to the individual wheel circuits. The EBTCM commands the valves to their correct position during an antilock or traction 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.
If the vehicle is equipped with Traction Control there are two TCS master cylinder isolation valves within the BPMV. These valves isolates the master cylinder so the pump motor can build brake fluid pressure for the front brakes during a traction event.
If the vehicle is equipped with Traction Control there are two TCS prime valves within the BPMV. These valves allow the pump to draw fluid from the master cylinder reservoir, through the compensating ports in the master cylinder bore.
The EBTCM performs the following primary functions:
The EBTCM also controls the display of the ABS and traction control DTCs while in diagnostic mode. The 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 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 EBTCM continues to control pressure in the individual hydraulic circuits until a slipping tendency is no longer present. The EBTCM continuously monitors the ABS/TCS for proper operation. If an error is detected, the EBTCM can disable the ABS/TCS and turn on the ABS or TRAC OFF Indicators in the IP, and Driver Information Display or Trip Computer.
The pump motor relay provides power to the pump motor during antilock braking and traction control. The solenoid valve relay provides power to the solenoid valves in the BPMV. Both of these relays are an integral part of the EBTCM and cannot be serviced separately.
A wheel speed sensor is located at each front wheel bearing assembly and at each rear wheel bearing assembly. The sensors use AC voltage in order to transmit wheel speed information to the EBTCM. Passing a toothed sensor ring past a stationary sensor causes the magnetic induction that generates the voltage. A pair of wires carry the signal to the EBTCM. The wheel speed sensors are located in their respective bearing assemblies and are not adjustable. The sensor gap is set at the time of assembly.
The Traction Control On/Off Switch (TRAC Switch) is a momentary on switch that allows the driver to shut off the ETS/TCS for personal or diagnostic reasons. Turning the switch to off places the ETS/TCS in the passive mode while maintaining ABS functions. With the ETS/TCS system on, pressing the switch disables the ETS/TCS and the TRAC OFF indicator turns on.
