The brake pressure modulator valve (BPMV) is mounted on the left front side of the engine compartment. The BPMV provides brake fluid modulation for each of the individual wheel circuits as required during DRP/ABS/TCS/VSES (if equipped). During DRP/ABS, 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 DRP/ABS.
With the exception of the EBCM, the BPMV is an integral, non-serviceable component. The BPMV should never be disassembled.
The BPMV uses a 4 circuit configuration with a diagonal split. Individual circuits are provided for the left front and right rear wheels, and 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.
The BPMV consists of several other components:
The BPMV contains a motor driven recirculation pump. The pump serves two purposes:
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 EBCM 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 EBCM performs the following functions:
The EBCM 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 commands appropriate valve positions in order to modulate brake fluid pressure in some or all of the hydraulic circuits. This prevents wheel slip and provides optimum braking. The EBCM continues to control pressure in individual hydraulic circuits until a slipping tendency is no longer present. If the EBCM detects an error, the EBCM can perform the following actions:
The EBCM transmits torque request signals to and receives delivered torque signals from the PCM.
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 EBCM 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 EBCM. 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 EBCM. 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 is a momentary switch that allows the driver to turn on or off the TCS for personal or diagnostic reasons. Pressing the switch places the TCS in the passive mode while maintaining ABS functions. With the TCS system on, pressing the switch disables the TCS and the TRAC OFF indicator turns on. If you press the switch again, TCS will become functional and the TRAC OFF indicator will turn off.
The Vehicle Stability Enhancement System (VSES) is also known as the Precision Control System (PCS) and the instrument cluster indicator lamp is labeled with the acronym PCS. The VSES consists of a yaw/lateral accelerometer sensor, a steering angle sensor, and a brake pressure sensor working in conjunction with the EBCM.
The yaw rate sensor and lateral accelerometer sensor are both in the same module and use a reference voltage of 5 volts. The lateral accelerometer sensor's operating range is 1.5 g resulting in an output range of 2.5 - 4.75 volts. The yaw rate sensor's range is 75 degrees/seconds, resulting in a signal proportional output of 0.25 - 4.75 volts. Zero yaw rate is 2.5 volts. The yaw/lateral accelerometer sensor is located inside the center console, between the automatic transaxle gear selector and the console storage compartment.
The steering angle sensor sends dual CAN signals to the EBCM. The EBCM determines steering wheel position and rotation using these signals. The steering angle sensor is located in the lower left hand side of the IP, on the bottom of the steering column.
The brake pressure sensor uses a reference voltage of 5 volts. The sensor's operating range is 0.25 - 4.75 volts. The EBCM uses input from the brake pressure sensor for more accurate control during a VSES event.
