ABS Description and Operation (Equal to or Over 8600 GVW): Notes

This vehicle is equipped with an EBC 345 ABS/EBD module.

This module provides the following vehicle performance enhancement systems:

• Antilock Brake System (ABS)
• Electronic Brake Distribution (EBD)

The following components are involved in the operation of the above systems:

• Electronic brake control module (EBCM)-The EBCM controls the system functions and detects failures.

  The EBCM contains the following components:

  • System relay-The system relay is internal to the EBCM. The system relay is energized when the ignition is ON. The system relay supplies battery positive voltage to the valve solenoids and to the ABS pump motor. This voltage is referred to as system voltage.
  • Solenoids-The solenoids are commanded ON and OFF by the EBCM to operate the appropriate valves in the brake pressure modulator valve (BPMV).
• Brake pressure modulator valve (BPMV)-The BPMV uses a 3-circuit configuration to control hydraulic pressure to each front wheel independently, and to the rear wheels as a pair.

  The BPMV contains the following components:

  • ABS pump motor and pump
  • Three isolation valves
  • Three dump valves
  • A front low-pressure accumulator
  • A rear low-pressure accumulator
• Wheel speed sensors (WSS)-EBCM sends a 5-volt reference voltage signal to each front wheel speed sensor. As the wheel spins, the wheel speed sensor produces a square wave DC signal voltage. The wheel speed sensor increases the signal frequency as the wheel speed increases, but does not increase the signal amplitude.