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. 3 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. 6 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 from 60 to 70 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. In display zone 2, the predefined pressure is displayed by the engine control unit (specification). The values for specification and actual value should be identical.

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

Note:

The readout must not fall below 5 bar, otherwise the engine will stall (this could damage the catalytic converter).

The readout in display zone 3 decreases (process takes between 2 and 3 minutes) 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. 6 bar.

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.
• ‒ If fault memory has been erased, you must generate readiness code again.