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16804 Efficiency below threshold question - help a numpty

Discussion in 'A4/A4 cabriolet/S4 forum(B6 chassis)' started by dope, Nov 8, 2010.

  1. dope

    dope alcoholic pervert

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    Please excuse this if it's blindingly obvious to you - My brain struggles with this stuff.

    I've been getting 16804 Cat system, bank1 Efficiency below threshold for some time now. I understand that this may be either a faulty O2 sensor or a knackered CAT. So normally you would change the sensor first because it's cheaper and cross your fingers it doesn't throw the code again.

    Given that the car just failed the MOT on emissions - O2 out of range - does that confirm beyond any doubt that it is in fact the CAT at fault?

    The O2 sensor and the MOT gas test are essentially reading the same thing?

    Money's tight so if I can 'just' change the CAT and save myself the £60 for the sensor that £60 goes toward other stuff to get the MOT sorted.


    Cheers
     
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  3. simon.m

    simon.m Active Member

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    is there not a way of say kiwick fit /ats telling you if your cat has gone there must be a way
     
  4. dope

    dope alcoholic pervert

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    Ha! According to my local Kwikfit everything needs replacing all the time.

    They'd fit tyres and advise me they'll need changing by the time I've driven across the car park.
     
  5. simon.m

    simon.m Active Member

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    i just found this on line mate may help you

    There are many signs that the catalytic converter may be in need of service, but two of the more common signs are engine performance and an odor associated with a failing converter.



    A converter that is damaged can cause the engine to not function properly. For example, the engine struggles when going up inclines, it hesitates when you try to accelerate or you experience a noticeable drop in fuel economy. If a tank of gas is not taking you as far as it used to, then it may be time to have the catalytic converter looked at.



    An imbalance in the air-to-fuel ratio can cause excessive amounts of sulfur to be burned during the converter's operation. This can result in a distinctive "rotten egg" smell that is often associated with burning sulfur. Do not ignore that burning smell if you experience it while driving your vehicle--it could be your catalytic converter in need of repair.

    Read more: Symptoms of Catalytic Converter Failure | eHow.com Symptoms of Catalytic Converter Failure | eHow.com
     
  6. aragorn

    aragorn "Stick a V8 in it!"
    Staff Member Moderator VCDS Map User

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    Assuming thats the ONLY fault code, and the MOT computer shows the cat isnt working (medium-high CO (circa 0.5-0.7%), medium-high HC (<500ish), normal lambda), then yes, i'd say the cat is dead.

    You said however the fault was that O2 was thru the roof, which implies to me that the engine is running lean, which may indicate the primary lambda is faulty, or a MAF or similar?
     
  7. dope

    dope alcoholic pervert

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    Cheers Simon. Not noticed any significant performance drop off, or the eggy smell, but I guess it could still have failed.

    Aragorn - sorry - when I said 'out of range' I didn't mean off the scale. Readings for typical fast idle test are

    CO 0.344 (limit is 0.300) - fail
    HC 12 (limit is 200) - pass
    Lambda 0.994 (limit min 0.970 max 1.030) - pass

    To confuse the issue it's not the only code. I also get

    16795 Sec.Air Inj sys
    incorrect flow detected

    Although I understand this won't affect anything when it's running at normal temp - only when starting from cold. Some kind of heat diverter issue or something.
     
  8. acano

    acano Member

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    Hi, I've been battling with this for over a year now! I have changed both sensors and also the cat, but still the light with this code triggers every few days I changed onto Vpower fuel and I now get a week between resettng the light. I would still like to get to the bottom of this so if you do come up with the answer please post back.
    BTW my emisions are fine with the last MOT and other checks done by the same garage since changing the cat.

    Tony

    2.0lt 2001 Saloon
     
  9. dope

    dope alcoholic pervert

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    acano - That sounds like a royal pain in the ass. I so don't want to shell out for a CAT only to find it doesn't fix the issue. I will let you know what develops though…

    What's a good price for a CAT anyway?

    (It's a '53 1.8T 190 Avant)
     
    #8 dope, Nov 8, 2010
    Last edited: Nov 8, 2010
  10. aragorn

    aragorn "Stick a V8 in it!"
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    Looks like the cat to me!

    Lambda and HC passed and are spot on, so the mixture is perfect meaning the main lambda is working properly, the CO didnt quite drop down low enough due to the cat being ineffective.
     
  11. iyrix

    iyrix Member

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    No one should ever use Kwick Fit. They are the biggest waste of time in the motor industry.

    I would never advise anyone to go near them!
     
  12. simon.m

    simon.m Active Member

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    did not mean for him to get it fixed there just tested
     
  13. iyrix

    iyrix Member

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    yeah i know, but they are very oftern wrong and alway want to replace everything.

    My boss took his A4 to them for rear brakes, they told him he needed calipers. Went round to Audi, they cleaned them and they were fine!

    I just stay well clear of the little buggers!
     
  14. acano

    acano Member

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    I paid 300 for one off the net, cant remember where though but if I get the chance I'll dig out the receipt and let you know


    Tony

    2.0 2001 Saloon
     
    #13 acano, Nov 8, 2010
    Last edited: Nov 8, 2010
  15. dope

    dope alcoholic pervert

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    Cheers - GSF just quoted me £120. That doesn't seem as painful as I was afraid it would be.

    I guess if the CAT is changed the O2 levels will pass the MOT, even if it doesn't stop the car throwing 16804 code…

    At least I'll be motoring again, just with that friggin orange light on all time.
     
  16. acano

    acano Member

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    Let me know what the quality of the cat from GSF, as my mate is in need of one too, and he is thinking about GSF as its a decent prince if the quality is ok

    cheers Tony
     
  17. dope

    dope alcoholic pervert

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    Will do.

    Don't know if you have an APD near you. They do one for £136 which isn't bad either I guess.
     
  18. dope

    dope alcoholic pervert

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    For future referance - this turned out to be the sensor. Changed it and the O2 came back into tolerance for the MOT.
     
  19. acano

    acano Member

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    Good stuff, cheapest first!
    I take it you never sent for the replacement CAT from GSF?


    thanks Tony
     
  20. dope

    dope alcoholic pervert

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    Yeah - could have been worse.

    Forgot what it's like not having that orange warning light on all the time. I have the steering wheel adjusted just right so it blocks it out! Feels like it pulls better around half throttle too.

    Probably only a matter of time before something makes the light come back on though.

    Anyway no - sorry didn't get to see what the GSF cat was like.
     
  21. acano

    acano Member

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    Outta curiosity which sensor did you change ?
     
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  23. dope

    dope alcoholic pervert

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    Lambda downstream of the cat. Apparently it took a little while after changing it for the O2 level to drop.
     
  24. aragorn

    aragorn "Stick a V8 in it!"
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    The lambda downstream of the cat shouldnt affect the fuelling whatsoever.

    The upper lambda does the fuelling, the second one is only there to ensure the cats working. It does this by comparing the readings between the two sensors, and if the cats working it expects them to differ by a certain amount.
     
  25. dope

    dope alcoholic pervert

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    Maybe it was that one then. Makes sense. I'll confirm with the garage that did it.
     

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