Audi A4

since 1994 of release

Repair and car operation



A4 Audi
+ Running gear
+ Regular servicing
+ Engines
+ Turbo-supercharging
+ exhaust System
+ cooling System
+ Fuel tank and fuel pump
+ Air filter and absorption channels
+ injection System
+ Coupling
+ Transmission and main transfer
+ Suspension bracket of wheels and steering
+ Brakes
+ Wheels and tires
- Electrotechnical equipment
   The minus is connected to weight
   The help for orientation in the electrotechnical equipment of the car
   Wires
   Connections of wires
   Central switching knot
   Support of additional relays
   Box for electronics
   Relay and control units
   Switching relay
   H-contact of the relay of unloading
   Table of the relay and control units
   Safety locks
   Table of safety locks
   + Electric circuits
   + Accumulator
   + Generator
   + Starter
+ ignition System
+ Lighting
+ Alarm equipment
+ Tools and devices
+ Heating and ventilation
+ body Details
+ Salon
Search of malfunctions
Technical characteristics





Relay and control units

A number of the relay and control units which are placed in a protective box at the left under a control panel or under facing of a steering column belongs to the onboard electrotechnical equipment.

  • The simple switching relay is used for powerful consumers of a current. If the current arrives long bypass ways on wires via the corresponding switches, there is a tension loss. Besides, contacts of switches are exposed to strong loading at the expense of a current of big force. At relay switching switches are used only for a small switching current thanks to what the consumer is connected not directly, and via the relay.
  • If the signal about switching goes not from the switch, and from the electronic control unit, the same law operates: sensitive electronic knots cannot carry out currents of big force without damages.
  • Certain relays can carry out additional functions. For example, the relay breaker of faltering impulses, the relay of switching of intervals in work of system of washing/clarification of glasses operates an interval in work and movement of screen wipers dry after washing of glasses.
  • Control units possess more or less extensive electronic schemes of switching of certain functions, one more relay is sometimes established also. As an example it is necessary to call the control unit the central lock and systems of the prevention of breaking.