Audi Workshop Service and Repair Manuals

The injection system consists of a high-pressure part (maximum
110 bar approx.) and a low-pressure part (approx. 6 bar).

Prior to opening the high-pressure part - e.g. when removing the high-pressure pump, fuel rail, injectors, intake manifold flap air flow control valve or any other component, or a fuel line located in the high-pressure zone of the injection system - the fuel pressure in the high-pressure part must be reduced to a residual pressure of approx. 8 bar. The appropriate procedure is described below.

Locate the fuse for the electric fuel pump using the current flow diagram.

=> Current Flow Diagrams, Electrical Fault-finding and Fitting Locations binder

• ‒ Unplug connector from activated charcoal filter system solenoid valve 1 -N80 (ACF valve); see Exploded view of fitting locations.
• ‒ Start engine and let it idle.

Note:

The engine control unit is selected below using the V.A.S 5051 and the display group 140 then selected under the function "Read measured value block".

• ‒ → Use diagnostic wire VAS 5051/1 to connect up vehicle diagnostic, testing and information system VAS 5051.

→ Readout on VAS 5051:

• ‒ Touch "Vehicle self-diagnosis" key.

→ Readout on VAS 5051:

• ‒ From list -1- select vehicle system "01 - Engine electronics".
• ‒ Wait until next readout appears.

→ Readout on VAS 5051:

•     1 -    Engine control unit identification.

• ‒ Touch ▸ key.

→ Readout on VAS 5051:

•     1 -    List of diagnosis functions:

• ‒ From list -1- select diagnostic function "08 - Read measured value block".

→ Readout on VAS 5051:

• ‒ Use keypad -2- to enter display group number 140 and confirm entry by touching Q key.

→ Readout on VAS 5051:

•     1 -    Display group X
•     2 -    Display zone 1
• Display zone 2
• Display zone 3
• Display zone 4

Watch the readout in display zone 3. When the engine is idling, a value of approx. 39 bar is shown in display zone 3. The readout shows the current pressure (actual pressure) in the fuel rail which is being generated by the high-pressure pump.

• ‒ Now remove fuse for electric fuel pump and continue to watch readout in display zone 3. Allow engine to continue idling.

The readout in display zone 3 decreases very quickly because the mechanical high-pressure pump is no longer being supplied with fuel from the fuel tank by the electric fuel pump.

• ‒ Switch off ignition when readout reaches approx. 8 bar.

Note:

The readout must not fall below 6 bar, otherwise the engine will stall (this could damage the catalytic converter).

The fuel rail is still full of fuel; the fuel is, however, no longer under high pressure.

Components or lines can now be opened. A clean cloth must be wrapped around the joints. Any discharged fuel must be collected.

• ‒ Interrogate and, if necessary, erase fault memory of engine control unit on completion of repair work.
• ‒ Generate readiness code in engine control unit in "Assisted fault-finding" mode.