Hydraulic Control Assembly - Antilock Brakes: Description and Operation

EBTCM/BPMV:

BRAKE FLUID MODULATION
The Brake Pressure Modulator Valve (BPMV) 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 Brake Pressure Modulator Valve (BPMV) is an integral, non-serviceable component. The BPMV should never be disassembled. 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 rear brake calipers.

NOTE: 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 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.

TCS Master Cylinder Isolation Valve
There is one TCS Master Cylinder Isolation Valve within the BPMV. This valve isolate the master cylinder so the pump motor can build brake fluid pressure for the rear brakes during a traction event.

TCS Prime Valve
There is one TCS prime valve within the BPMV. This valve allow the pump to draw fluid from the master cylinder reservoir, through the compensating ports in the master cylinder bore.