Audi A4

since 1994 release

Repair and operation of the car



A4 Audi
+ Running gear
+ Regular servicing
+ Engines
+ Turbo-supercharging
+ System of an exhaust
+ Cooling system
+ Fuel tank and fuel pump
+ Air filter and channels of absorption
+ System of injection
+ Coupling
+ Transmission and main transfer
+ Suspension bracket of wheels and steering
+ Brakes
+ Wheels and tires
- Electrotechnical equipment
   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
+ System of ignition
+ 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 under a control panel or under facing of a steering column at the left belongs to the onboard electrotechnical equipment.

  • The simple switching relay is used for powerful consumers of current. If current arrives in the long bypass ways on wires via the corresponding switches, there is a loss of tension. Besides, contacts of switches are exposed to strong loading at the expense of current of big force. At relay switching switches are used only for small switching current thanks to what the consumer is connected not directly, and via the relay.
  • If the signal of switching goes not from the switch, and from the electronic control unit, the same law works: 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 the movement of screen wipers dry after washing of glasses.
  • Control units possess more or less extensive electronic schemes of switching of certain functions, also one more relay sometimes is installed. As an example it is necessary to call the control unit of the central lock and systems of the prevention of breaking.










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