The BPMV is mounted on the left front side of the engine compartment. The BPMV provides brake fluid modulation for each of the individual front wheel circuits and each of the rear wheel circuits together as required during antilock braking. The BPMV maintains or reduces brake fluid pressure independent of the pressure generated in the master cylinder during the antilock mode. The BPMV cannot 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 3-circuit configuration during normal braking. Individual circuits are provided for the left-front and the right-front wheels and for both rear wheels together. The front and the rear circuits are hydraulically isolated so that a leak or a malfunction in one circuit will allow continued braking ability of the other.
The BPMV contains a small pump motor. The pump circulates brake fluid back to the master cylinder circuit during the antilock mode. The pump is located in the BPMV and cannot be serviced separately.
The solenoid valves of the modulator are an integral portion of the BPMV and are not serviceable. The solenoid valves increase, decrease or maintain brake fluid pressure to the individual circuits. The solenoid valves are controlled by the EBTCM which commands the valves to their correct positions during antilock braking. The valves are positioned to pressure increase or open during normal braking. The pressure in each hydraulic circuit can increase, decrease or maintain constant by changing the valve position to various combinations during the antilock mode.
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.
The EBTCM is a small, control microprocessor. The EBTCM monitors the speed of each wheel and monitors the electrical status of the brake pressure modulator valve.
The following are the primary functions of the EBTCM:
The EBTCM controls the display of the ABS and traction control diagnostic trouble codes while in the diagnostic mode.
The EBTCM contentiously checks the speed of each wheel to determine if any wheel is beginning to lock. The EBTCM commands the appropriate valve positions to modulate the brake fluid pressure in some or all of the hydraulic circuits if a wheel locking tendency is detected. This prevents wheel lockup and provides optimum braking. The EBTCM continues to control the pressure in individual hydraulic circuits until a locking tendency is no longer present. The EBTCM also commands the ECM to perform engine torque reduction and commands the TCM to prevent transmission down-shifting during traction control mode.
The ABS with TCS is electrically monitored by the EBTCM for proper operation. If the EBTCM detects an error it disables the antilock and traction control function and turns on the ABS or TC indicator lamps in the instrument cluster. Refer to Self-Diagnostics for further information regarding the ABS self diagnosis and further information regarding the EBTCM DTCs.
A wheel speed sensor is present at each front wheel and at each rear 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 a toothed sensor ring past a stationary sensor. The signal is transmitted to the EBTCM through a pair of wires.
The front wheel speed sensors are mounted in the front steering knuckles. The front wheel speed sensors are non-adjustable. The sensor gap is set at time of assembly. The connectors for each speed sensor are located near the wheelhouse panel.
The rear wheel speed sensors are mounted at each end of the differential housing. The rear wheel speed sensors are non-adjustable. The sensor gap is set at the time of assembly.
The speed of each toothed sensor ring is measured separately. The front wheel hydraulic circuits are controlled individually based on front wheel speed signals. The rear wheel hydraulic circuits are controlled together based on which ever rear wheel speed signal is indicating the lowest speed.
The electronic traction control switch is located in the instrument panel.
The electronic traction control switch is a momentary contact switch used to enable or used to disable the traction control system. The switch assembly consists of a momentary contact press button switch. The TCS can be enabled and can be disabled during an ignition cycle by pressing the switch. The TCS resets to enable if the ignition switch is cycled to the OFF position then back to the RUN position. This insures a consistent state at startup for the driver.
The TCS will disable when the electronic traction control switch is pressed. The amber TC indicator lamp in the I/P will turn on to indicate the system has been disabled. The TC indicator lamp will turn off and the TCS reactivated by pressing the switch again.
The TCS will default to on if the switch is held down for 15 seconds or longer, as this will be interpreted by the EBTCM as a malfunction in the switch circuit.
The wiring harness is the mechanism by which the EBTCM is electrically connected to the following:
The following are the components considered part of the wiring harness:
