ABS Description and Operation: Notes
WARNING: This page is about a different car, the 2003 GMC Safari and 2003 Chevrolet Astro. However, it is still accessible from the selected car via links, so may be relevant.
This vehicle is equipped with the Kelsey-Hayes EBC325 antilock braking system.
The vehicle is equipped with the following braking enhancement systems:
- Anti-lock Brake System (ABS)
- Dynamic Rear Proportioning (DRP)
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 solenoid valves and to the pump motor. This voltage is referred to as system voltage.
- Solenoids - The solenoids are commanded by the EBCM to operate the appropriate valves in the brake pressure modulator valve.
- Brake Pressure Modulator Valve (BPMV) - The BPMV uses a 3-circuit configuration to control the left front wheel, the right front wheel, and the combined rear wheels. The BPMV directs fluid to the left front and right front wheels independently. The BPMV directs fluid to the two rear wheels on a single hydraulic circuit.
The BPMV contains the following components:
- Pump Motor
- Three isolation valves (one for each hydraulic circuit)
- Three dump valves (one for each hydraulic circuit)
- A front low-pressure accumulator
- A rear low-pressure accumulator
- Wheel Speed Sensors (WSS) - As the front wheels spin, a toothed ring located at each wheel hub interrupts a magnetic field in the wheel speed sensors. This causes the wheel speed sensors to generate an AC signal. The EBCM uses this AC signal to calculate the wheel speed. The wheel speed sensors are replaceable only as part of the wheel hub and bearing assemblies. Any imperfections in the toothed ring, such as a missing or damaged tooth, can cause an inaccurate WSS signal.
- Vehicle Speed Sensor (VSS) - The input signal for rear wheel speed originates with the VSS. The Powertrain Control Module (PCM) receives rear wheel speed information from the VSS and supplies this information to the EBCM via a serial data message.