1, 2 and 3 Digit Codes: 2

Fault Code 1 through 4 Diagnosis Chart:

Wheel Circuit Valve Electrical Circuit:

WHEEL CIRCUIT VALVE OPERATION
Hydraulic pressure to the wheel circuits are controlled by the four wheel circuit valves contained in the valve block. The ABCM can command these valves into any of three different modes. Valve position is determined by the amount of current flowing through the valve coil.

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

Pressure Hold Mode
The ABCM commands the pressure hold mode when it desires to hold the pressure constant in the wheel circuit. This position will not allow fluid to flow to or from the master cylinder and is used during anti-lock control. The pressure hold mode is set when approximately 2 amps flows through the valve coil.

Pressure Reduce Mode
The pressure reduce mode 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 assembly reservoir during anti-lock control. The pressure reduce mode is set when approximately 4 amps flows 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.

WHEEL CIRCUIT VALVE OPERATION
When valve operation is desired, the ABCM regulates the appropriate amount of current to flow into the wheel valve coil to set the desired mode.

WHEEL CIRCUIT VALVE SELF TEST
The ABCM constantly monitors valve line voltage to compared it to expected values. If the values do not match, an ABS fault code is set. In addition, the valves are actively tested during the system self test at key-on. When the vehicles first reaches approximately 4 mph after key-on, the ABCM cycles each valve and checks for proper response. This test (BITE) may be heard as a clicking or popping noise when the vehicle first starts moving.