ABS prevents the wheels from locking during sudden braking. As a result, the car remains controllable during full braking.
ABS operates as soon as the ignition is on and the speed is 5-7 km/h. It regulates all braking processes in the locking area as soon as the speed exceeds 12 km/h.
The speed of rotation of the wheel is measured by means of speed sensors, two for the front and two for the rear wheels. By analyzing the signals from the individual speed sensors, the electronic control unit calculates the average speed, which corresponds approximately to the average speed of the car. By comparing the rotation speed of an individual wheel and the average rotation speed of all wheels, the control unit recognizes the slipping state of an individual wheel and can thus detect the state of the wheel shortly before it locks.
The possibility of wheel locking means that the brake fluid pressure in the corresponding brake mechanism is too high in relation to the wheel's grip on the road, in which case the hydraulic system, receiving signals from the control unit, maintains the fluid pressure constant. Namely, the pressure in the brake mechanism does not increase, even if you press the brake pedal harder. If the possibility of locking remains, the fluid pressure decreases when the release valve opens, but only so much that the wheel accelerates slightly, then the pressure is again maintained constant.
If the wheel accelerates more than a certain value, the pressure of the hydraulic system increases again, but not above the value of the total brake pressure.
This operation is repeated under hard braking for each individual wheel until the brake pedal returns to its original position or shortly before the car comes to a complete stop.
A safety device in the electronic control unit ensures that the ABS, in the event of a malfunction, (for example, a break in the circuit) or the voltage of the on-board network is too low (battery voltage less than 10.5 V) switched off by itself. In this case, the ABS control light on the instrument panel lights up while driving. The regular braking system remains functional. The car behaves when braking as if ABS was not installed.
If the ABS indicator light comes on while driving, this is a signal that the ABS system has been disabled. In this case, you should:
- stop the car for a while, turn off the engine and start it again;
- check battery voltage;
- if the voltage is below 10.5 V, charge the battery.
Caution! If the ABS indicator light comes on when you start driving and goes out again after a while, this indicates that the battery voltage was initially too low, but then increased as a result of recharging from the generator.
Examination
1. Check the tightness and good contact of the battery terminals.
2. Place the car on jacks, remove the front wheels, check the speed sensor wiring for external damage.
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3. Further checks should be carried out at a service station.
Attention! Before welding with an electric welding device, it is necessary to disconnect the plug from the electronic control unit (installation location: behind the driver's door pillar trim). The plug should only be disconnected when the ignition is off, do not start driving with the plug disconnected. During painting work, it is permitted to expose the control unit to short-term temperatures of up to + 90°C and long-term temperatures of up to + 90°C (about 2 hours) up to + 85°C.
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