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Volker L.

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Brake booster not venting properly | AUDI A4 Allroad B8

Hello,

After installing a brake booster including master cylinder, I can't get the system completely free of air. Even after repeated bleeding (with a bleeder), the brake pedal remains soft.

ABS warning light is on.

What can I do? Thank you

Already checked

The solution provided is based on experience and general automotive service knowledge.

#Engine

AUDI A4 Allroad B8 (8KH)

💬14

Solution

Volker L.

So... I think everything's fine again. 👍☺ When stationary without the ignition on, I have full pressure on the pedal. With the engine running, the pedal gives way a little, as it should, and the ABS light stays off. I turned the rear brake calipers so that the bleed valve was at the highest point and some more air came out. Then I bled everything again with the ignition on (I read that this opens the valves in the hydraulic unit).

Comments (14)

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  1. Hans V.

    Tester only!!

    1
  3. Florian A.

    It is possible that the system has not been completely bled. With VAG, you sometimes need a diagnostic device (e.g. VCDS) to bleed the system correctly. Especially when replacing larger components in the brake system, air remains in the system. You then have to bleed several times with a tester and instructions….

    5
  4. Andreas W.

    If the ABS pump was completely emptied, bleeding with a diagnostic device (VCDS) is necessary, whereby the ABS pump is activated for approx. 10 seconds.

    Control unit 03 Brake electronics

    Basic setting 04

    then group 002 and start.

    3
  5. Alexander P.

    Nowadays, you have to flush the ABS with a tester, because air can get trapped in the ABS, as the valves have to be opened to get the air out.

  7. Volker L.

    Yes, I had already heard that from a car mechanic friend. 👍...I'll try it out. Otherwise, I won't be able to avoid having the whole thing done with a diagnostic device. 😣 Thanks!

  8. Volker L.

    Thanks again... I'll try that out. It's the cheapest option for now. 😁

    4
  9. Martin2672

    That's exactly how it was for me too

    2
  10. André B.

    With the Golf 5, there was the issue with the rear calipers and the bleeding problem.... someone mentioned the video by the Docs... Such a replacement is only possible (as already mentioned) with a diagnostic tester or in-depth diagnostics. Otherwise, you won't get all the air out. If problems still persist, I would try tilting the brake calipers to allow the air to escape more easily...

    3
  11. Kai W.

    I had that problem too. You can only get the air out with a tester. When bleeding, tilt the saddle at the rear (as in the video), that's where the remaining air is trapped.

  12. Justin S.

    You need to bleed the ABS module using a diagnostic tool

  13. Volker L.

    Yes, that will be the problem 👍👍 ....I'll get to work on it right away.

  14. Volker L.

    Yep, sounds good... Thanks ☺