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Fault code 16804 - Catalyst System

Discussion in 'A4/A4 cabriolet/S4 forum(B6 chassis)' started by acano, Nov 20, 2009.

  1. acano
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    acano Member

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    [Nov 20, 2009]
    Ok so i keep getting this fault code thrown up, not really sure why, but I took my car into audi again, to get it checked. Came back that the cat is fine no holes (none they can see anyway) and they said that the sensors were fine, but on the same breath said I should maybe change the sensors to see if that will sort the problem.
    seems a bit strange considering they said all was fine!

    so anyway done a bit of a search and found this was wondering if anyone had used one before or even thought it might work?
    any thoughts?

    Tony
    #1
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  3. Woorlord
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    Woorlord shifting to Hyperspace... . VCDS Map User

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    [Nov 21, 2009]
    Assuming A4/1.8T?

    DTC Error according to Bentley Manuals......

    P0420 16804 Catalyst System Efficiency Below Threshold Bank 1

    It says checks to do:

    1. Heated Oxygen Sensor (H02S) -G39- and oxygen sensor regulation before catalytic convertoer checking
    2. Oxygen sensors and oxygen sensor regulation behind catalytic converter checking
    3. Test-ID 01 Catalytic converter

    PM me and i can probably pdf the 3 procedures to you via email!
    #2
  4. acano
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    acano Member

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    [Nov 23, 2009]
    thanks for reply
    the car is an A4 2.0 SE B6
    but i'll try to get these checked anyway
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  5. Woorlord
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    Woorlord shifting to Hyperspace... . VCDS Map User

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    [Nov 28, 2009]
    Sent you an email with pdf with the relevant checks for DTC 16804.

    My manuals list them for the 1.8T - but sensor information should still be relevant to your 2.0, as both petrol.
    #4
  6. acano
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    acano Member

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    [Nov 29, 2009]
    fantastic thanks:rock:
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  7. audipardner
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    audipardner Member

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    [Jan 10, 2010]
    Did you ever get to the bottom of this as I've lived with this error code for quite some time now. Lots done to rectify but still there.
    #6
  8. acano
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    acano Member

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    [Jan 10, 2010]
    so far both sensors replaced still there so looks like a new cat but i need to save a little first:(
    #7
  9. audipardner
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    audipardner Member

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    [Jan 11, 2010]
    Have you checked all your pipes, breather hoses etc. I had a couple of splits in mine but changing them didnt make any difference unfortunately.

    This is what I've done so far:
    New MAF
    Both Lambdas
    Breather hoses
    New Cat - aftermarket, bought from cats 2 go IIRC???. About a third cheaper than the stealers but only carries a two year guarantee - vice 3 for Audi. My Indy said that it didnt flush fit exectly to the exhaust manifold but managed to get it on....maybe there is still a leak from that???
    Piece of insulating tape over the Engine light!!! - Promotes forgetfullness that the problem still exists!!

    Is the car running rich? This would also cause the light to come on - High CO levels IRO 0.3% upwards is MOT fail at fast idle, then default for ALT engine at normal idle is 0.5% to pass.

    Before new Cat, check rubbers, exhaust manifold for leaks and even give your MAF a clean with IPA (isoprop alcohol). Read how to's on this before you do though!!

    Hope you have better luck than me.

    Dougie

    2.0 Sport ALT Engine
    #8

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