1, 2 and 3 Digit Codes: 12

Fault Code 12 Diagnosis Chart:

Valve Relay Circuits:

RELAY OPERATION
The valve relay is included in the sensor block assembly and, when engaged, provides power to the hydraulic wheel circuit valves and the replenishing valve. Battery power is also provided to the valve relay feedback line at the Anti-lock Brake Control Module (ABM) whenever the relay is engaged. The pressure monitoring module controls current flow through the valve relay coil based on commands from the ABCM and accumulator pressure inputs. The pressure monitoring module is also a part of the sensor block assembly.

Pressure Monitoring Module
The pressure monitoring module controls most electrical operations in the hydraulic assembly, including the following;
(1) Pump/Motor Control. The Pressure Monitoring Module contains two redundant pressure switches which sense accumulator pressure. These switches signal the module to switch the pump/motor relay on and off in order to keep the accumulator pressure in its proper operating range.
(2) BRAKE Warning Lamp Control. The module can turn on the BRAKE warning lamp in the event of low accumulator pressure or an internal pressure switch failure. It does so by grounding the warning pressure lines (ABCM Pin 3).
(3) Valve Relay Control. The module grounds the valve relay coil when commanded to do so by the ABCM. The ABCM turns the valve relay on by grounding the valve relay actuation line. The pressure monitoring module can disable the valve relay without being told to do so by the ABCM in the case of very low accumulator pressure and internal module failures.
(4) System Fault Communication. The module communicates low pressure conditions and other internal problems to the ABCM by means of the Warning Pressure Line (ABCM Pin 3).

Circuit Operation
With the valve relay disengaged, all valve lines and the valve relay feedback line to the ABCM (Pin 32) are held to ground by the relay. When the valve relay feedback line is held to ground, the Anti-lock Brake System (ABS) Fault line (ABCM Pin 29) is also held to ground through Diode D1. When the ABS Fault line is held to ground, anti-lock function is disabled, and the ANTI-LOCK warning lamp is illuminated by grounding the lamp through Diode D1.

The valve relay is engaged during normal system operation. At key-on, the ABCM commands the valve relay on by grounding the valve relay actuation line, (ABCM Pin 28). When the pressure monitoring module senses that the valve relay actuation line has been grounded, the module provides a ground for the valve relay coil. With the relay engaged, battery power is provided to the valves and the valve relay feedback line (ABCM Pin 32). The valve relay will remain engaged until the ignition is turned off, unless a failure is detected and the ABCM or Pressure Monitoring Module command the valve relay to disengage.

FAILURE CONDITIONS
When the valve relay is engaged, the valve relay feedback line (ABCM Pin 32) should be at battery voltage. With the valve relay disengaged, the feedback line should be at ground. If the commanded position of the valve relay and the valve relay position indicated by the feedback line do not agree, Fault Code 12 will set. Note that this code can set due to a failure in the pressure monitoring module, the valve relay or by an over/under voltage condition.