Audi 80/Avant (B4)

since 1991-1995 release

Repair and operation of the car

Audi 80/Avant
+ Technical specification
+ Engines
+ System of production of the fulfilled gases
+ Cooling system
+ Fuel tank and fuel pump
+ Air filter and airintaking channels
+ System of injection
+ Coupling
+ Transmission and transmission
+ Suspension bracket and steering
+ Brake system
- Anti-blocking system of brakes
   Basic elements
   Malfunctions of ABS
+ Wheels and tires
+ Body electrical system
+ System of ignition
+ Lighting
+ Signaling devices
+ Devices and auxiliary devices
+ Heating and ventilation
+ Body elements
+ Search of malfunctions
+ Specifications

Basic elements

Hydraulic block

The hydraulic block (2) of anti-blocking system is located in a motor compartment behind at the left. If to remove a protective cover (1), then the relay of electromagnetic valves (3) and the relay of the returnable pump (4) are visible.

It is located in a motor compartment at the left behind: the hydraulic block is between the brake pipeline from the main brake cylinder and the brake pipeline to wheel brakes. According to teams of an electronic control unit pressure in the brake system is supported to constants, decreases or created again. However this pressure cannot be higher than what is created in the main brake cylinder after pressing of a pedal of a brake by the driver. Regulation of pressure is carried out by four quickly we vklyuchayushchimitsya by valves with the electromagnetic drive – on one on a wheel.

If on valves food does not arrive, pressure increases. At the maximum giving of food there is a pressure decrease, at average food pressure is supported to constants. The pressure decrease phase is especially interesting: as it is impossible to give the brake fluid arriving from the main brake cylinder it is simple to go to a receiver (otherwise thereof the brake pedal just would fail), the powerful returnable pump pumps over brake fluid back to the main brake cylinder. You notice this process on a brake pedal which begins to pulse slightly if the returnable pump works, that is ABS comes into effect. If to listen, then it is possible to hear also noise of the pump. The noise isolation in the hydraulic block slightly muffles sounds of operation of the pump.

Above on the hydraulic block two more relays are located along with shtekerny connection. Bigger of them gives food to the returnable pump; through the smaller relay there passes the control of electromagnetic valves.

Rotation frequency sensors

Frequency of rotation of each separate wheel is determined by the rotation frequency sensor (all their four pieces) and transfers this information to the control unit. In return the control unit gives team to the hydraulic block.
Sensors of frequency of rotation consist of the magnetic core and the coil and are installed at small distance from a gear washer – a rotor. A rotor, – as it is already clear according to the name, – rotates together with a wheel why gear cambers on its perimeter depending on speed pass near the sensor quicker or more slowly. Each tooth running under the sensor causes in it short-term increase in tension. Thus, in the sensor the electric impulse changing the frequency according to rotation frequency is created. The signal arising thus is processed in the control unit as information on rotation frequency. Rotors are located ahead on external hinges of the leading half shafts and behind on naves of wheels.

Electronic control unit

In the Sedan the control unit of anti-blocking system (shooter) is located under a back seat at the left. In the versatile person this control unit is placed under the left side covering of a luggage compartment.

Similar sensors of frequency of rotation (shooter) are located in the car equipped with anti-blocking system on all four wheels.

The control unit is located under back sitting at the left and processes the arriving signals from rotation frequency sensors. At the same time it operates the hydraulic block so that wheels were not blocked. Along with difficult processing of signals and the logic following this element the control unit contains also the scheme of blocking. With its help the device can check itself, distinguish external mistakes and control working tension. If malfunctions are established, ABS is disconnected, on the dashboard the control bulb lights up.


Three relays participate in work of ABS:

  • The relay of electromagnetic valves is located under a cover on the hydraulic block.
  • The relay of the returnable pump is also located under a cover on the hydraulic block.
  • The ABS step relay and the relay of protection against retension are assembled in the combined relay.

Main switch

The models produced to 07.92 g.

By means of the main switch located on the panel of switches on the dashboard at the cars released till July of 92 g it is possible to disconnect ABS in order that in extreme road conditions it was possible to reach some reduction of a brake way. So, for example, if on the road filling brick is scattered or ice is covered with snow, when braking in front of tires