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Annoying P0171 (Bank 1 Lean) Issue

phey708 May 17, 2019

  1. phey708

    phey708 New Member


    I have been trying to diagnose an annoying CEL on my car that keeps appearing. When clearing it takes a while to come back but it does come back eventually. I have used a diagnostic wireless tool to try and troubleshoot why the P0171 issue appears. I have done some data logging and the only issue I can find is that the Short Term Fuel Trim spikes to -25% but only after I have lifted off from WOT.

    When idling, I am getting between 1% and -3% for the short term fuel trim and when driving I get between 5% and -5% with occasional 10% or -10% but not that often. The MAF on WOT is showing 175 g/s which works out at about 220bhp which is what my engine is rated anyway. Fuel pressure is around 1740psi on WOT as well and goes to around 725psi on idle which again I think is normal for the 2.0TFSI engine. I can't see the fuel delivery or MAF being at fault and with the fuel trims not much during idle I can't see it being a vacuum issue.

    I have also replaced evaporation value and PCV valve too and I have also pressed the brake pedal during idle to make sure no vacuum is escaping (the fuel trims doesn't change) from the servo to the intake manifold. Is there anything else I can check?

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  3. Sonny Singh

    Sonny Singh Audi A4 DTM

    I had a similar thing. Try changing the purge valve in the engine. Don’t know if that’s the same as the evaporation valve but That cured mine and a cheap and easy fix

    Sent from my iPhone using Tapatalk
  4. phey708

    phey708 New Member

    Hi the purge valve/n80 valve was one of the first things that I changed.


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