Sensor Block
The sensor block is mounted on the left side of the booster/master cylinder assembly and contains several electrical components. All electrical communication between the hydraulic unit and the Electronic Brake Control Module (EBCM) takes place through the sensor block. The following connectors are included on the sensor block:
- Control Pressure Switch (2-pin, on front of sensor block)
- Reed Block (2-pin, on booster/master cylinder assembly)
- Valve Block (12-pin, behind sensor block cover)
- Sensor Block Main Harness Connector (1S-pin, on top of sensor block)
- Hydraulic Unit Ground (single pin, on the front of sensor block below the control pressure switch connector)
- Pressure Monitoring Module (controls pump operation and provides a low pressure warning)
The sensor block also contains the valve relay and pressure monitoring module which are critical to system operation.
The valve relay is contained in the sensor block and provides power to the five solenoid valves. When the valve relay is not energized, it provides a path to ground for the valve circuits and the ABS fault line. The Electronic Brake Control Module (EBCM) controls the valve relay through an input to the sensor block pressure monitoring module. The valve relay is energized during normal operation.
The pressure monitoring module controls pump operation, by grounding the pump relay coil, in response to changes in hydraulic accumulator pressure. The pressure monitoring module contains two pressure switches, if these switches do not indicate the same pressure, the sensor block will turn on the Red BRAKE warning lamp and disable anti-lock function. The pressure monitoring module will also turn on the BRAKE lamp and disable anti-lock (by turning off the valve relay) if low accumulator pressure is detected.
The reed block is an integral part of the booster/master cylinder assembly. It is not serviced individually. The reed block contains two switches which communicate booster piston travel information to the EBCM. A 2-pin connector is used to connect the reed block to the sensor block. The reed block switches are used along with the control pressure switch and the brake light switch to monitor hydraulic unit operation.