DTC 03

Wiring Diagram:

VALVE OPERATION

The valve block contains four valves for control of hydraulic pressure in the wheel circuits. These valves may be commanded into three different positions by the EBCM. Valve position is determined by the amount of current which is allowed to flow through the valve coil.

Pressure Increase

The pressure increase position is the normal operating position of the valve for braking without anti-lock control. This position allows brake fluid to flow to and from the master cylinder as in a standard brake system. The valve remains in the pressure increase position when no current is flowing through the valve coil.

Pressure Hold

The pressure hold position is commanded when the EBCM desires to hold the pressure in the wheel circuit constant. This position will not allow fluid to flow to or from the master cylinder and is used momentarily during anti-lock control. The pressure hold position is commanded by allowing a current of approximately 2.0 amps to flow through the valve coil.

Pressure Reduce

The pressure reduce position is used to decrease hydraulic pressure in a specific wheel circuit without decreasing pressure in the rest of the system. This position redirects fluid from the wheel circuit to the hydraulic unit reservoir and is used momentarily during anti-lock control. The pressure reduce position is commanded by allowing a current of approximately 4.0 amps to flow through the valve coil.

VALVE POWER

The valve circuits receive power through the valve relay. The valve relay is engaged at key-on and remains engaged throughout the ignition cycle. Valve lines should have battery voltage available at all times.

VALVE OPERATION

When valve operation is desired, the EBCM allows the appropriate amount of current to flow into the EBCM, thereby placing the valve in its proper position.

VALVE SELF-TESTING

Valve line voltage is constantly monitored by the EBCM and compared with expected values. if expected values do not match actual voltages, an ABS trouble code is set. Additionally, the valves are actively tested each key cycle. When the vehicle first reaches approximately 4 mph after key-on, the EBCM cycles each valve and checks for proper response. This test may be heard as a slight "popping" or "ticking" noise when the vehicle first starts moving.