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Technical data > < Rules for cleanliness and instructions for working on fuel system

A4 Cabriolet Mk2

Important: Required procedure prior to opening high-pressure injection system
Important: Required procedure prior to opening high-pressure injection system
   
If the battery is not disconnected, the fuse -28- for the fuel pump control unit -J538- must be removed as a precaution before opening the fuel system, because the fuel pump will otherwise be activated by the contact switch on the driver's door.
  Note
t  The fuse is located in the fuse holder in the dash panel.
t  Removing fuse -28- will interrupt the voltage supply “terminal 30” for the fuel pump control unit -J538-.
  Caution
The injection system consists of a high-pressure section (maximum approx. 110 bar) and a low-pressure section (approx. 6 bar).
Prior to opening the high-pressure section (e.g. when removing the high-pressure pump, fuel rail, injectors, fuel pipes or fuel pressure sender -G247-), the fuel pressure in the high-pressure section must be reduced to a residual pressure of approx. 6 bar. The procedure is described below.
Reducing fuel pressure in high-pressure section
Special tools and workshop equipment required
  A97-0242
t  Assembly tool -T10118-
  W00-1148
–  Using assembly tool -T10118-, detach electrical connector -2- from fuel pressure regulating valve -N276-.
–  Allow engine to idle for about 10 seconds.
  Note
t  Fuel pressure will be reduced from approx. 50 bar to approx. 6 bar when electrical connector is detached from fuel pressure regulating valve -N276- while engine is idling.
t  You can watch the fuel pressure dropping by connecting a vehicle diagnosis and service information system -VAS 5052 A- and selecting the engine control unit. Select function “Read measured value block” and display group 140.
t  The fuel pressure (actual value) is displayed in zone 3.
–  Switch off ignition.
  WARNING
The fuel lines are still filled with fuel, however the fuel is no longer under high pressure. Wear safety goggles and protective clothing when opening the fuel system to avoid possible injury and skin contact.
Before opening the high-pressure section, wrap a cloth around the connection.
–  The high-pressure system can be opened after reducing the pressure; wrap a clean cloth around the connection and allow the remaining pressure in the system (approx. 7 bar) to dissipate. Catch the escaping fuel.
  Note
The pressure may increase again slightly if a high-pressure line is not opened immediately.
–  Connect vehicle diagnosis and service information system -VAS 5052 A- and generate readiness code in engine control unit using “Guided Fault Finding” mode.
  A24-10141

Technical data > < Rules for cleanliness and instructions for working on fuel system