The brake pressure modulator valve (BPMV) mounted on the left front side of the engine compartment, provides brake fluid modulation for each of the individual wheel circuits as required during ABS/TCS/VSES (if equipped). During the ABS 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 normal braking.
With the exception of the EBCM, 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 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 which are described as follows:
The BPMV contains a motor driven recirculation pump. The pump serves 2 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 4 inlet, and 4 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 ABS/TCS/VSES. During ABS 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.
There are 2 TCS master cylinder isolation valves within the BPMV. These valves isolate the master cylinder so the pump motor can build brake fluid pressure for the front brakes during TCS/VSES. Unlike the ABS valve solenoids, the isolation valves do not modulate. They are normally open and then close during TCS/VSES.
There are 2 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 prime valves also do not modulate. They are closed during normal operation and open during TCS/VSES.
The EBCM performs the following functions:
The EBCM 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 commands appropriate valve positions 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 EBCM also receives suspension signal from and sends steering wheel position signals to the CVRSS module.
The pump motor relay provides power to the pump motor during ABS/TCS/VSES. The solenoid valve relay provides power to the solenoid valves in the brake pressure modulator valve (BPMV). Both of these relays are an integral part of the EBCM and cannot be serviced separately.
The EBCM defines a drive cycle as the completion of the EBCM initialization sequence. The EBCM will perform the initialization sequence one time in each ignition cycle. Refer to Initialization Sequence .
The traction control switch is a momentary on switch that allows the driver to shut off the TCS for personal or diagnostic reasons. Turning OFF the system places the TCS in passive mode while retaining ABS functions. When the TCS system is turned OFF, the TRACTION OFF message is displayed on the DIC. The switch is located in the instrument panel compartment, on the left side.
The stoplamp switch is an input to the EBTCM. The EBCM uses the stoplamp switch to tell when the brake pedal is being applied so that TCS can be disabled if necessary.
A wheel speed sensor (WSS) is present at each wheel. The sensors transmit wheel speed information to the EBCM by means of a small AC voltage. This voltage is generated by magnetic induction caused by passing the toothed sensor ring (part of the integral hub/bearing assembly) past the stationary sensor. The signal is transmitted to the EBCM through shielded wiring to help reduce electro-magnetic interference that can cause false or noisy WSS inputs to the EBCM.
The wheel speed sensors are mounted in the hub/bearing assembly and are non-adjustable. Sensor gap is set at time of assembly.
Pin 16 of the EBCM harness connector is a plastic vent tube that vents the cavity between the EBCM and the BPMV to the passenger compartment.
The lateral accelerometer is a self contained unit which uses a reference voltage of 5 volts. The sensor's operating range is ±1.5 g, resulting in an output range of 0.25-4.75 volts. Zero lateral acceleration results in an output signal of 2.5 volts.
The yaw rate sensor is a self contained unit which uses a reference voltage of 5 volts. The sensor's range is ±75 degrees/second, resulting in a signal proportional output of 0.25-4.75 volts. Zero yaw rate is 2.5 volts.
The steering wheel position sensor (SWPS) incorporates two distinct sensors in one housing. This is done for ABS/TCS/VSES/CVRSS (if equipped). The CVRSS needs high resolution analog steering information over a limited range of travel. The ABS/TCS/VSES uses a digital signal with the resolution of 1 degree over the full range of travel.
