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 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 serves two purposes:

1. During ABS reduce pressure events, it transfers fluid from the brake calipers back to the master cylinder.
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.

ABS Valves

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/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.

TCS Master Cylinder Isolation Valves

If the vehicle is equipped with traction control there are 2 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.

TCS Prime Valves

If the vehicle is equipped with traction control 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 EBCM/EBTCM performs the following primary functions:

The EBCM/EBTCM also controls the display of the ABS and traction control 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/TCS for proper operation. If an error is detected, the EBCM/EBTCM can disable the ABS/TCS and turn on the ABS or TRACTION OFF Indicators in the IPC.

The brake lamp driver module contains electronic components that turn the ABS indicator on unless the EBCM/EBTCM provides a ground to turn the indicator off (inverter). If the EBCM/EBTCM loses power or is disconnected the brake lamp driver module commands the ABS indicator on. The brake lamp driver module is located on the RH side, behind the instrument panel cluster.

Vehicles, that are either a Pontiac or equipped with a UB3 instrument cluster and have TCS, have a brake lamp driver module with dual independent circuits for the ABS and TRACTION OFF indicators. Vehicles that do not have TCS are equipped with a single circuit brake lamp driver module for the ABS indicator.

The traction control switch is a momentary on switch that allows the driver to shut off the TCS for personal or diagnostic reasons. Turning the switch to off places the TCS in the passive mode while maintaining ABS functions. With the TCS system on, pressing the switch disables the TCS and the TRACTION OFF indicator turns on.

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/EBTCM. Passing a toothed sensor ring past a stationary sensor causes the magnetic induction that generates the voltage. A pair of wires carries the signal to the EBCM/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.

Pin 16 of the EBCM/EBTCM harness connector is a plastic vent tube that vents the cavity between the EBCM/EBTCM and the BPMV in the passenger compartment.