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B5 A4|S4 Boost Gauge Installation

contributed by: jakecro[ww]



    Boost Gauge

    10 ft. of 1/8" I.D. vacuum tubing

    6 ft. of wire for power and ground (2 lenghts)

    proper vacuum connections needed to connect your specific gauge


    1. Remove center vent cluster.  (I installed my gauge prior to completing this write-up)

    2. Remove vent in which you want to place the gauge.

    a. Pry the vent out gently using a small flat head screwdriver, working from both sides of the vent.

    b. Take out the side-to-side vent adjustment.

    3. Measure the vent for the gauge to begin cutting.

    a. Place the gauge on the back of the vent and mark the vent ribs to the outside of the face.  Now, adjust your marks to match the diameter of the gauge BODY not the face.  (With the VDO unit I used I needed to make approx. a 1/8” adjustment to the diameter.  Remember it is always better to cut the opening slightly smaller and make fine adjustments to have the gauge fit snugly in the vent.)

    b. I used a coping saw to rough out the opening followed by dremel/file to finish it off.

    4. The gauge was sanded quickly and painted with Plasti-Dip paint to blend with the vent

    5. A hole was cut into the lower left corner of the air duct using a drill and an Exact-O knife to allow for the vacuum hose and power wires to pass through.

    6. Feed the wires and hose down through the dash and over near the power distribution block.

    7. I connected the red power wire to the far left stud to provide switched power that stays lit while the ignition is ‘on’ just as the instrument cluster is.

    8. Connect the black wire to ground.  (See the group of brown wires going to the bolt to the left of the power distribution block.)

    9. Now feed the vacuum hose up into the ECU box following the large bundle of wires.

    a. To do this you will need to remove the knee bolster and the under dash kick panel.

    b. There is one 8mm bolt holding the panel in place on the right side.  Remove this bolt and the panel will lower allowing you to remove the ODB-II connector as well as the light connection.   Now slide the panel toward the driver’s seat allowing the ‘hooks’ to release that hold the rear of the panel in place.

    c. Remove the two plugs in the knee bolster and subsequently removing the 8mm bolts.

    d. Pull the fuse panel access cover to remove the final 8mm bolt and then removing the knee bolster.

    e. Notice: it is not required to remove the bolster but it will give better access to the area under the dash.

    10. Remove the cowl cover giving access to the ECU box followed by the four (4) 7mm bolts securing the lid.  Next, release the clip securing the ECU and pull the hose through.  Be sure to route the hose so it does not interfere with the ECU’s placement while not creating a pinch point in the hose itself.

    11. Cut a small opening in the rubber membrane that exits the ECU box toward the engine to allow for the vacuum hose to pass through.

    12. Route the hose over near the brake booster and out through the firewall plug between the brake booster line and the coolant expansion tank.

    13. Splice a ‘T’ fitting into the vacuum line going to the fuel pressure regulator.  (If the current vacuum hose is frayed or cracking you should replace the entire hose between the intake manifold and the fuel pressure regulator.)

    a. If you are using a mechanical gauge you will get some noise within the gauge unless you use some sort of restrictor in the line.  I took a straight 1/8” hose fitting and partially melted it to restrict the air flow slightly.  Not the ideal solution but it was cheaper than sourcing a restrictor fitting.

    14. Once you have double checked all of your connections it would be suggested to start the car to assure that the gauge is working. 

    15. Just follow the steps in reverse to put it all back together and enjoy your work!

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