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Am i experiencing limp mode/n75 open circuit fault

Discussion in 'A3/S3 Forum (8L Chassis)' started by iamramaz, Jun 4, 2012.

  1. iamramaz
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    iamramaz New Member

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    [Jun 4, 2012]
    Originally I thought i had a problem with a coil pack as car felt like it was intermitently running on 3 cylinders. since getting VCDS i have a fault code:
    17956/P1548/005448 - Boost Pressure Control Valve (N75): Open Circuit

    would this be causing limp mode, the car really runs rough/ shakes on acceleration. After stopping for a few minutes and restarting it runs normal. Is limp mode like this?

    Thanks in advance
    #1
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  3. Paddya3turbo
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    Paddya3turbo Member

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    [Jun 4, 2012]
    From what Iv worked out this controls the boost pressure that's built up so if it's constantly open surely no pressure is building ??? Don't hold me to that I ain't got a clue lol !!! But I'd deffo be ordering another from eBay or Audi
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  4. marty.h
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    marty.h Member

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    [Jun 5, 2012]
    The N75 bleeds air of to the actuator so raises the boost its possible your car could be over boosting and going into limp mode if the valve has stuck open. I'm posting from my phone so can't get a link for you but if you have a poke about you will find how to test it with a multi meter and what ohms it should be across the pins. But if that code is stored and won't clear I would first check the connections and make sure they connecting well if not a new N75 will be needed

    Sent from my BlackBerry 8520 using Tapatalk
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  5. ayfreetee
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    ayfreetee Member

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    [Jun 5, 2012]
    Try unplugging the electrical connector and start the car to see if it runs any better, if so then you know the N75 is at fault, they are about £40 new on eBay.
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  6. <tuffty/>
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    <tuffty/> Badger 5 Edition Staff Member Moderator

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    [Jun 5, 2012]
    It won't be causing limp mode but will feel like limp mode... is this the only fault code? try running with the N75 unplugged... if the car runs smoothly but with no power (as it will be running on actuator pressure with the N75 disconnected) then there would appear to be an issue with the N75 or more likely the wiring... if the engine is still running a bit rough then its not the N75...

    If you are intermittently running on 3 cyls like you say then its plausible you have a wiring fault... the wiring to the coil packs tends to melt and crack over time and could be causing the issue... as the wiring shares earths too a break in one earth could effect many other components... it does sound like the open circuit issues and the misfire could be related... the N75 being a victim of another fault

    If the car still runs badly after unplugging the N75 then start tracing the wiring back... typical areas is the earth on the cam cover (and any damaged wiring in the coil pack loom) and earths under the battery tray...

    <tuffty/>
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  7. iamramaz
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    iamramaz New Member

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    [Jun 5, 2012]

    Cheers will look into these things first
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  8. iamramaz
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    iamramaz New Member

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    [Jun 6, 2012]
    Problem seems to be fixed. broken down coil pack plugs, 2 wires shorting in wiring loom & 1 coil pack changed.

    Thanks again to those who gave advice.
    #7

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