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For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 2001 🢒 GMC C-Series Medium Duty Truck B7 🢒 Brakes 🢒 Antilock Brake System 🢒 ABS Description and Operation

EBCM and BPMV
Object Number: 650882 Size: MF
(1)Electronic Brake Control Module (EBCM)
(2)Brake Pressure Modulator Valve (BPMV)

BPMV Hydraulic Flow
Object Number: 468767 Size: LF
(1)Master Cylinder Reservoir
(2)Master Cylinder
(3)Pump
(4)Brake Pressure Modulator Valve (BPMV)
(5)Damper
(6)Right Rear Isolation Valve
(7)Accumulator
(8)Right Rear Brake
(9)Right Rear Dump Valve
(10)Left Front Dump Valve
(11)Left Front Brake
(12)Left Front Isolation Valve
(13)Left Rear Isolation Valve
(14)Left Rear Brake
(15)Left Rear Dump Valve
(16)Right Front Dump Valve
(17)Right Front Brake
(18)Accumulator
(19)Right Front Isolation Valve
(20)Damper

This vehicle is equipped with the EBC410M antilock braking system.

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

    • 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 4-circuit configuration to direct fluid to the left front, right front, left rear, and right rear wheels independently.
        The BPMV contains the following components:
       - Pump motor
       - Four isolation valves (one for each hydraulic circuit)
       - Four dump valves (one for each hydraulic circuit)
       - A front low-pressure accumulator
       - A rear low-pressure accumulator
    • Wheel speed sensors (WSS) - As the 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.

Initialization Sequence

The EBCM performs one initialization test each ignition cycle. The initialization of the EBCM occurs when the following conditions are met:

    • The ignition is ON.
    • The bulb check has been completed.
    • Vehicle speed is greater than 6 km/h (4 mph).

The initialization sequence briefly cycles each solenoid and the pump motor to verify proper operation of the components. The EBCM sets one or more DTCs in accordance with any malfunction that is detected.

The EBCM defines a drive cycle as the completion of the initialization sequence.

Antilock Brake System

When wheel slip is detected during a brake application, the ABS enters antilock mode. During antilock braking, hydraulic pressure in the individual wheel circuits is controlled to prevent any wheel from slipping. A separate hydraulic line and specific solenoid valves are provided for each wheel. The ABS can decrease, hold, or increase hydraulic pressure to each wheel brake. The ABS cannot, however, increase hydraulic pressure above the amount which is transmitted by the master cylinder during braking.

During antilock braking, a series of rapid pulsations is felt in the brake pedal. These pulsations are caused by the rapid changes in position of the individual solenoid valves as the EBCM responds to wheel speed sensor inputs and attempts to prevent wheel slip. These pedal pulsations are present only during antilock braking and stop when normal braking is resumed or when the vehicle comes to a stop. A ticking or popping noise may also be heard as the solenoid valves cycle rapidly. During antilock braking on dry pavement, intermittent chirping noises may be heard as the tires approach slipping. These noises and pedal pulsations are considered normal during antilock operation.

Vehicles equipped with ABS may be stopped by applying normal force to the brake pedal. Brake pedal operation during normal braking is no different than that of previous non-ABS systems. Maintaining a constant force on the brake pedal provides the shortest stopping distance while maintaining vehicle stability.

Pressure Hold

The EBCM closes the isolation valve and keeps the dump valve closed in order to isolate the slipping wheel when wheel slip occurs. This holds the pressure steady on the brake so that the hydraulic pressure does not increase or decrease.

Pressure Decrease

If a pressure hold does not correct the wheel slip condition, a pressure decrease occurs. The EBCM decreases the pressure to individual wheels during deceleration when wheel slip occurs. The isolation valve is closed and the dump valve is opened. The excess fluid is stored in the accumulator until the pump can return the fluid to the master cylinder or fluid reservoir.

Pressure Increase

After the wheel slip is corrected, a pressure increase occurs. The EBCM increases the pressure to individual wheels during deceleration in order to reduce the speed of the wheel. The isolation valve is opened and the dump valve is closed. The increased pressure is delivered from the master cylinder.

ABS Indicator

The ABS indicator illuminates when one or more of the the following occur:

    • The EBCM detects an ABS-disabling malfunction.
    • The EBCM performs the bulb check.
    • The EBCM does not power up or loses power during the igniton cycle.
    • The ground circuit between the ABS lamp relay and the EBCM becomes open.