When ABS is activated, a rapid pulsation is felt on the brake pedal. This pulsation is caused by rapid changes in the position of individual electromagnetic valves that are activated to prevent the wheels from locking. This pulsation occurs only when ABS is activated and stops as soon as normal braking is restored or when the car stops. The presence of extraneous sounds and pulsation when ABS is activated is not a malfunction.
Vehicles equipped with ABS can be stopped by simply pressing the brake pedal, and the brake pedal operates in the same way during normal braking as non-ABS systems. Maintaining a constant force on the brake pedal ensures shorter braking distances while maintaining vehicle stability. A typical ABS cycle is as follows:
Pressure retention
The electronic brake control unit closes the isolation valve and holds the bleed valve closed to isolate the locked wheel when slippage is detected. The pressure value remains constant, neither increasing nor decreasing.
Reducing pressure
If the wheel continues to slip while the pressure is maintained, the pressure in the brake line decreases. The electronic brake control unit reduces the pressure in the brake circuits of individual wheels when wheel lock is detected. The isolation valve is closed and the bleed valve opens. Excess fluid flows into the accumulator until the pump returns it to the expansion tank or master cylinder.
Increase in pressure
After the wheel stops slipping, the pressure in the brake line increases. The electronic brake control unit increases the pressure in the brake circuits of individual wheels to reduce their rotation speed. The isolation valve opens and the bleed valve closes. The pressure increase occurs due to the fluid coming from the main brake cylinder.
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