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 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 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 two purposes: 1) During ABS reduce pressure 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 reservoir 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.
There are two 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 a traction event. Unlike the ABS valve solenoids, the isolation valves do not modulate. They are normally open and then close during a traction event.
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 prime valves also do not modulate. They are closed during normal operation and open during a traction event.
The function of the EBTCM is to monitor the wheel speed sensor (WSS) inputs, determine wheel slip tendencies, control the brake system while in antilock mode or a traction event and monitor the system for proper operation.
The 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 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 EBTCM continues to control pressure in individual hydraulic circuits until a slipping tendency is no longer present. If the EBTCM detects an error, it can disable the antilock brake system, traction control and Stabilitrak® functions and turn on the ABS and/or TRACTION CONTROL lamp in the instrument cluster. It can also command the driver's information center (DIC) to display antilock, traction control, or Stabilitrak® messages via Class 2 serial data line. The EBTCM transmits torque request signals to and receives delivered torque signals from the PCM. The EBTCM also receives signals from the suspension controller if equipped.
The pump motor relay provides power to the pump motor during ABS and TCS. 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.
The traction control disable switch is a momentary on switch that allows the driver to shut off the TCS for personal or diagnostic reasons. Turning the system off places the TCS in passive mode while retaining ABS functions. The switch is located in the center console.
The stoplamp/BTSI switch is an input to the EBTCM. The EBTCM uses the stoplamp/BTSI switch to tell when the brake pedal is being applied so that traction control can be disabled if necessary.
A wheel speed sensor (WSS) is present at each wheel. The sensors transmit wheel speed information to the EBTCM 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 EBTCM through shielded wiring to help reduce electro-magnetic interference that can cause false or noisy WSS inputs to the EBTCM.
The front wheel speed sensors are located in the hub/bearing assembly and are non-adjustable. Sensor gap is set at the time of assembly.
The rear wheel speed sensors are mounted in the bearing assembly and are non-adjustable. Sensor gap is set at the time of assembly.
Pin 16 of the EBTCM harness connector is a plastic vent tube that vents the cavity between the EBTCM and the BPMV to the underhood engine harness to body harness connector.
The lateral accelerometer sensor 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 lateral accelerometer sensor is located under the rear drivers side seat, attached to the number four bar.
The yaw rate sensor is a self contained unit which uses a reference voltage of 5 volts. The sensor's range is ±64 degrees/second, resulting in a signal proportional output of 0.25-4.75 volts. Zero yaw rate is 2.5 volts. The yaw rate sensor is located in the left hand corner of the rear compartment, under the rear shelf behind the rear compartment lid hinge.
The steering wheel position sensor (SWPS) incorporates two distinct sensors in one housing. This is done for ABS/TCS/ICCS and CVRSS. The CVRSS needs high resolution analog steering information over a limited range of travel. The ABS/TCS/ICCS uses a digital signal with the resolution of 1 degree over the full range of travel.
