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S3 mot failure on emissions please help

campbell Sep 29, 2011

  1. campbell

    campbell Member

    My 2002 audi S3 went in for MOT and the co2 emission pass mark is below 0.2, mine was reading ridiculously high at 5.2!

    Took it to an audi specialist and the car has thrown up no faults, no warning lights, they recommended putting cat cleaner in it so I durn that and retested it but still the same readings!

    Car is serviced regular, any ideas!? Please help
  2. Alex C

    Alex C Well-Known Member VCDS Map User Audi S3

    have you discontected any sensors recently and forgotten to reconnect them? ... although i would have thought that would throw a fault
  3. colicabcadam

    colicabcadam Guest

    rag the **** off the car, put some decent fuel in it (97+ ron)

    failing that it could be any of the following

    spark plugs, injectors, egt sensor, lambda sensor (i believe there's 2?), coils, cat, water temp sensor

    easy thing to do would be to check oen of the sparks, get a CLEAR picture of one (or all of them) and then someone on here will tell you if you are running lean or rich
  4. Robbo1144

    Robbo1144 Faster in reverse

    posibly a lambda sensor on its way out.... i would do a vcds log on MAF and lambda readings, and injector cycles if you can.

  5. campbell

    campbell Member

    Thanks for the input guys. I always use v power, the car is in the specialist now so can't get any pics unfortunately of the spark plugs. I haven't disconnected any sensors and I thrashed it to the specialist down country roads. I hole it's not cats!
    The specialist said he co2 emissions coming out of the engine are usually 1.2 and then the cats take the reading down below 0.2 to pass the mot.....therefore that doesn't suggest to me that cats are buggered!?
  6. s3dave

    s3dave TFSI Hybrid Supporter

    Dirty air filter, as said get the exhaust glowing and it should sail through...i know it sounds daft but are you sure you have got a cat/s yeah?
  7. campbell

    campbell Member

    Yea the cars are there pal, garage tried another lambda probe but it made it worse
  8. Broken Byzan

    Broken Byzan Photographic Moderator Staff Member Moderator VCDS Map User Audi A4 quattro

    C02 is normally engine related, i would be looking at blocked breathers and / or old oil. Either of those can cause high C02 readings.

    the cat will have almost no impact on C02 readings unless its actual missing from the car altogether. Does it smke out of the oil filler cap when the car is running?
  9. jdas03

    jdas03 Member

    Mine failed initially as i drive the car to work a few miles down the road at low speeds everyday.
    They guy held the car in neutral at 4k revs for 5 - 10 mins to clear it all out.
    Sorted the problem and it passed no problems! try giving it a really good thrashing if like me you drive like a granny 90% of the time!
  10. aragorn

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

    Its got to be sensor related. A Healthy engine with no cat usually clocks around 0.5%, so if your cat had failed you'd expect to see figures around that point.

    either lambda or MAF, or perhaps a large air leak or similar.
  11. DJ_Troopa

    DJ_Troopa K1 Driver

    Mate don't worry about it too much, this happens to me every year lol.

    Go to Halfords, buy Wynns Injector Cleaner and stick it in the car. Do a drive down the motorway for about 20 mins doing 70-80 and give it a blast here and there. As soon as you get back to your area go get your emissions test and watch how it passes first time! :) So book your MOT test again and before you go do what i said above and go straight to your test after. My MOT man said this is a common thing with petrol Audi's.
  12. campbell

    campbell Member

    Cheers for all the replies guys....Just got the car back and through its MOT. Turned out to be a dirty exhaust sensor, the terminals were green so they cleaned them, the the probe/sensor on the other end was also dirty so they cleaned that end up, refitted and the emissions dropped to 0% with another can of cat cleaner. Sailed through the MOT, thank god it wasnt the cats. The fuel economy is a lot better, and the performance is smoother so happy days, cost me £90. That exhaust sensor is supposed to cost 200 ish new

    Cheers Again
  13. GemmaLouise

    GemmaLouise New Member

    I Have an Audi A3 1.6 8v my emissions are reading at 9% i have change the exhaust system to a 2 1/4 inch cat back system i need to know if my car has 1 or 2 lambda sensors??


  14. Sandip

    Sandip Well-Known Member Team Nogaro Blue

    Not 100% sure Gemma but i'd say it'll have 2, one before the cat and one after.

    It'll be the lambda before the cat that'll be causing issues with emissions if it's gone. If you can make sure the car has been driven hard before getting tested it may get through, the hotter the cat the more efficiently it'll work :)

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