DTC 12

VALVE 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. When the valve relay is engaged, battery power is also provided to the valve relay feedback line at the EBCM. The pressure monitoring module, which is also a part of the sensor block assembly, controls current flow through the valve relay coil based on commands from the EBCM and accumulator pressure inputs.

Pressure Monitoring Module

The pressure monitoring module controls most electrical activity in the hydraulic unit, including the following functions:

1. Pump Motor Control. The pressure monitoring module receives an accumulator pressure input from two switches in the sensor block assembly. The module then commands the pump on and off to adjust accumulator pressure to its normal operating range. See Pump Circuit information for more detail.

2. BRAKE Warning Lamp Control. The pressure monitoring module also can turn the BRAKE warning lamp on in the event of low accumulator pressure or an internal pressure switch failure.

3. System Fault Communication. The module communicates low pressure conditions and other internal problems to the EBCM by means of the system fault line.

4. Valve Relay Control. The pressure monitoring module grounds the valve relay coil when commanded to do so by the EBCM. The EBCM commands 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 EBCM in the case of very low pressure and internal module failures.

CIRCUIT OPERATION

With the valve relay disengaged, all valve lines and the valve relay feedback line to EBCM pin 32 are held to ground by the relay. When the valve relay feedback line is held to ground, the ABS Fault line (EBCM pin 29) is also held to ground through the ABS diode. The ABS fault line is also connected to Body Computer Module (BCM) pin 3D3. When the ABS fault line is held low, anti-lock function is disabled and the BCM displays the "ANTI-LOCK DISABLED" message on the Climate Control Driver Information Center (CCDIC).

The valve relay is engaged during normal system operation. At key-on initialization, the EBCM commands the valve relay on by grounding the valve relay actuation line (EBCM 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 (EBCM pin 32). The valve relay will remain engaged until the ignition is turned off, unless a failure is detected and the EBCM or pressure monitoring module command the valve relay to disengage.

FAILURE CONDITIONS

When the valve relay is engaged, the valve relay feedback line (EBCM 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, ABS Code 12 will set.