7.18. Anti-blocking system (ABS)

As special equipment of VW T4 has the anti-blocking BOSCH (ABS) system. The additional ABS installation is not possible.

ABS interferes with blocking of wheels at sharp braking. Thereof, at full braking the car remains operated.

ABS works as soon as ignition and speed of the movement is included makes 5–7 km/h. It regulates all brake processes in the field of blocking as soon as speed exceeds 12 km/h.

Thanks to RPM meters, on two on forward and on back wheels, the speed of rotation of a wheel is measured. Analyzing signals of separate RPM meters, the electronic control unit calculates the average speed which corresponds to approximately average speed of the car. Thanks to comparison of speed of rotation of a separate wheel and average speed of rotation of all wheels, the control unit distinguishes a condition of slipping of a separate wheel and can catch thereby a condition of a wheel shortly before its zablokirovaniye.

The possibility of blocking of a wheel means that pressure of brake fluid in the corresponding brake mechanism is too big in relation to coupling of a wheel with the road, in this case the hydraulic system, receiving signals from the control unit, supports liquid pressure to constants. Namely, pressure in the brake mechanism does not rise even if to press a brake pedal stronger. If the possibility of blocking remains, then pressure of liquid decreases when opening the final valve, but only so that the wheel slightly accelerated, then pressure is again supported to constants.

If the wheel accelerates stronger than a certain value, then pressure hydraulic system increases again, however values of the general brake pressure are not higher.

This operation repeats at sharp braking for each separate wheel until the pedal of a brake does not return to a starting position or shortly before a full stop of the car.

The safety device in an electronic control unit watches that ABS, in case of malfunction (for example break in a chain) or too low voltage of onboard network (tension of the rechargeable battery less than 10,5 In) itself was disconnected. In this case the control bulb of ABS on a guard of devices lights up during the movement. The usual system of braking keeps working capacity. The car behaves when braking so, as if ABS also is not established.

If during the movement the control bulb of ABS lights up, then it is a signal that the ABS system was disconnected. In this case follows:

  – to stop for a while the car, to kill the engine and again to start;
  – to check tension of the rechargeable battery;
  – if tension lower than 10,5 In to charge the rechargeable battery.


If the control bulb of ABS lights up with a start of motion and after a while dies away again, it indicates that tension of the rechargeable battery was too little in the beginning, but then rose as a result of recharge from the generator.


1. To check reliability of an inhaling and good contact of plugs of the rechargeable battery.
2. To install the car on a trestle, to remove forward wheels, to check an electrical wiring of RPM meters for external damages.
3. To make further check on HUNDRED.


Before welding works as the electrowelding device it is necessary to disconnect the plug from an electronic control unit (an installation site: behind a covering of a rack of a door of the driver. To disconnect the plug only at the switched-off ignition, not to begin the movement with the disconnected plug. During the paint and varnish works it is allowed to subject the control unit to influence of short-term temperature to + 90 °C and long (about 2 hours) to + 85 °C.