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
+ Wheels and tires
- Body electrical system
   Minus to "weight"
   Orientation in the electrical system
   Plug connections
   Central switchboard
   Additional block of the relay
   Relay and control units
   Unloading relay of contact of X
   Safety locks
   Table of safety locks
   Electric circuits
   + Full electroscheme of the Audi 80 car: 2-liter 4-cylinder engine (66 kW)
   + 2-liter 4-cylinder engine (85 kW)
   + 2,3-liter 5-cylinder engine (98 kW)
   + 2,6-liter 6-cylinder engine (110kvt)
   + Additional equipment
   + Battery
   + Generator
   Check of a condition of a maple or polilinovy belt
   Tension of a maple belt
   Tension of a maple or poliklinovy belt
   The belt torn maple
   Engine overheat because of damage of a maple belt
   Review of maple and poliklinovy belts
   Replacement of a maple belt
   List of malfunctions
   List of malfunctions
+ System of ignition
+ Lighting
+ Signalling devices
+ Devices and auxiliary devices
+ Heating and ventilation
+ body Elements
+ Search of malfunctions
+ Specifications

Relay and control units

Look under a back seat of Audi 80 of the version a sedan

1 – control unit of blocking of differential (only all-wheel drive models);
2 – switch of longitudinal acceleration of anti-blocking system (only all-wheel drive models);

3 – control unit of anti-blocking system;
4 – additional block of the relay.

On an illustration on the additional block of the relay (2) under a back seat of a sedan of Audi 80 the double relay (1) anti-blocking system is necessary. This relay can be used in the cars equipped as appropriate and as the relay of protection against an overstrain of system of inclusion of a safety cushion. On the same place it is possible to deliver also to the relay of electronic blocking of differential (EDS). The nearby cell 21 in sedans usually remains empty. In the following cell 20 the relay of a screen wiper of back glass of the Audi 80 station wagon is inserted. In a cell 19 (near outer side of the car) the relay of shutdown of back fog lights installed on models with a factory complete set the traction coupling device (turnbuckle) is located.

A number of the relay and control units located in the central switchboard or on the additional block of the relay at the left under the dashboard or under a back seat belongs to the onboard electrical system.

The simple switching relay is used first of all to powerful consumers of current. It has the following basis: if to carry out food on long cable lines via the corresponding switches, losses of tension will be a consequence. Besides, contacts of switches are exposed to big loading because of bigger current. At the relay scheme the switch is used only for low current, thus the consumer of current, and its relay is connected not directly.

If the switching team arrives not from the switch, and from the control unit, the same picture: sensitive electronic elements cannot carry out big currents without prejudice to themselves.

  • Certain relays can carry out additional functions. So, the relay of the index of turn includes blinking impulses, and the relay of system of washing of glasses and a screen wiper operates faltering action and work without screen wiper water after washing of glasses.
  • Control units are supplied with more or less difficult electronic systems for certain functions, sometimes in them also the relay is installed. As an example it is possible to call the control unit of power windows or the control unit of a delay of shutdown of light in salon.

Principle of operation of the switching relay

  • At inclusion of the corresponding consumer of food in the relay the electric chain from the plug 86 (the arriving "switching current") to the plug 85 becomes isolated (case).
  • Thanks to it an electromagnet, overcoming spring resistance, attracts powerful contact and thus closes an electric chain for "working current".
  • For prevention of losses of tension working current is carried out on the shortest way directly to the plug of 30 relays and from there further – on condition of the closed contacts via the plug 87 to the consumer of food.
  • Sometimes also the plug 87 meets and. It is rigidly connected with the plug 87, that is carries out the same function.

Search of malfunctions of switching relays


  1. On the plug 30 always there has to be tension, in that case if this is not about the relay which consumer depends on other consumer. Example: tension on the relay of a back fog lamp moves only if the light is turned on.
  2. For verification of tension to take (to put forward) the relay and to touch with a needle electrode of a control bulb the plug 30 in a relay socle. Lack of tension means a rupture of a wire.
  3. To remove the relay, to connect the plug 86 to a positive pole of the battery, and the plug 85 to the case ("weight"). The coil of an electromagnet has to (is clearly audible) to attract contact of the relay, otherwise the relay is faulty.

The help at the defective switching relay


  1. To take out the relay from a nest.
  2. To connect plugs 30 and 87 in a relay cell by means of an office paper clip or a short slice of a wire. Thanks to it the corresponding consumer will receive a direct current.
  3. For shutdown to remove this crossing point as the corresponding switch in this case is bypassed.

On uncovered (7) central switchboards in a short form (6) the possible arrangement of the relay and safety locks is displayed. In the same place there are small plastic flat-nose pliers for a detachment of safety locks. In the central switchboard various relays (1), plugs are visible to diagnostic units (2), safety locks 1–21 (3), and also additional safety locks 23-32 (4). Further four spare safety locks are placed (5).