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S3 Failed MOT on emissions

Discussion in 'A3/S3 Forum (8L Chassis)' started by s3jack, Mar 25, 2010.

  1. s3jack
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    s3jack New Member

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    Hi Everyone!

    Long time browser of the forum but first time posting, hope you can provide some advice:icon_thumright:

    Put the car through an MOT yesterday (2001 S3 Totally standard recently serviced etc) and it passed on everything except the emissions, the mechanic who i took it too (Deutsch tech local audi specialist) ran some injector cleaner through the car and gave it a good run and warm up but failed again on the second attempt.

    Im getting some mixed opinions on how to get the emission levels down, the mechanic who i took it too doesnt think the lambda probe is faulty as he can see it 'switching' and thinks the cat is by its best and needs replaced. A few other people i have spoke with reckon that the cat shouldnt fail and it will be a probe, i have ran vagcom with no errors returned.

    Does anyone have any advice before i spend any money on what this could be, are the cats known to fail on the s3? at the moment im thinking of going down the lambda sensor as it would be the cheapest.

    Cheers!
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  2. Maz
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    Maz Moon is made of green cheese

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    Not sure about cats failing but when mine failed on emissions it was one of the Lambda probes which showed up when scanned.

    Is the engine management light on?
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  3. s3jack
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    s3jack New Member

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    Hi, thanks for the reply :)

    Theres no engine management lights on and no error codes when scanned which is strange as you would think there would be somthing if either the sensor or cat was faulty, when your's failed with emissions was your ecu light on mate? after reading the emissions failure sheet the readings are out by a good bit and also come to think of it when sitting at idle for a few minutes i do get a faint petrol smell if standing outside the car..dont know if that would point to the faulty sensor?

    Cheers
    #3
  4. Welly
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    Welly VX220 SC Driver :)

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    Hmmmm. I would say if it was the Lambda being problematic, it would be the one directly after the turbo - on the down pipe. Malfunctioning devices don't always throw a code up. I've had a MAF in tthe past which was faulty - but working to a degree, and because it was giving data, the ECU didn't throw a code due to the fact that it was reporting data back.

    The point here is that it wasn't reporting the CORRECT data back to the ECU. This may be the case with your Lambda. The lambda may be functioning and reporting data back tot the ECU meaning that the ECU believes it to be OK. However, it might not be returning the correct reading.

    For example - if it is acting inefficiently, it is likely that it will report LESS fuel in the exhaust gas - meaning MORE fuel going in to the engine, resulting in failing emissions test, faint smell of fuel etc.

    The problem is, it's not a cheap item to replace. A genuine Bosch one (From Euro Car Parts) cost me £80 ish I think.

    The question is this: Is it worth a punt for £80 for it to maybe fix it? Or is it worth spending a LOT more on a cat to maybe not fix it.... It's either one or the other. Start with the cheaper.
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  5. Maz
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    Maz Moon is made of green cheese

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    I'm sure I got the light on the dash when mine failed and the car wasnt running as quick as it should have been.

    Facelift S3's have two probes but without any codes you can't tell which ones had it.

    If your gonna change them make sure you get OEM parts.
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  6. Welly
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    Welly VX220 SC Driver :)

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    So do pre facelifts. One pre cat and one post cat. It's normally the pre cat one which shafts your emissions - the second lambda doesn't really have much impact on fuelling - it's just there to report back the cat's effectiveness.


    Yes. Make sure you either get a Bosch one (OEM) or just get one from Audi. Expect it to be expensive from Audi though. Around £120 IIRC.
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  7. s3jack
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    s3jack New Member

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    Thanks for all the advice:friends:
    im going to go for the lambda sensor change first, the sensor just off the turbo seems to be the faulty one i would think to give the incorrect readings,and as has been said i would rather spend around £80 on a new sensor than a much more expensive cat! if its still failing after the sensor change then i guess it would be the cat, im going to phone the mechanic who done the mot and ask him why he thinks its the cat as at first he said it would be the sensor and then said he could see it 'switching' not sure what that means but i will report back :)
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  8. Welly
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    Welly VX220 SC Driver :)

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    I would imagine he means he can see it on the diag reporting data back.

    Like I said - not necessarily the correct data.
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  9. badger5
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    badger5 RIP S3dave Site Sponsor

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    what aspect of emissions did it fail?
    lambda?
    CO?
    hc?
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  10. s3jack
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    s3jack New Member

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    Hi :)

    It failed the c0 emissions, i dont have the print out here but on first test the limit i think was 0.3 and it reached 0.65, and then fast idle again limit i think was 0.3 but was hitting 1.56.

    is it reasonably easy to swap the sensors over going to attempt to do this myself after i buy the new one!

    Cheers
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  11. Welly
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    Welly VX220 SC Driver :)

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    LOL, top one on the downpipe not the easiest to get to. You WILL need a can of butane or propane gas to heat it up to crack it off. Not much working room so this makes the job much easier.

    Remove the charge pipe and you have reasonable access. Not a difficult job, but not easy at the same time.
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  12. s3jack
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    s3jack New Member

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    thanks for the info man :)

    i see you ordered your sensor from euro car parts, im probs going to get it from there as well however they have alot of different ones listed at different prices and they all seem to be bosch! this is the one i can see so far to get its for the a3 1.8 turbo but guess it would fit

    http://www.eurocarparts.com/ecp/c/A...9e4926f6570c0159ab3d8d62fc5a475f89ab&LAMSwhat do you think the right one?

    cheers
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  13. s3jack
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    s3jack New Member

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  14. Welly
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    Welly VX220 SC Driver :)

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    Yeah, that looks about right. Thats the same money I paid for mine. Did you put your reg number in to find it?

    Anyway, the extra work is simply cutting the plug for the loom off of the old lambda and soldering/bullet connector on. Job done.
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  15. bansheeboyo
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    bansheeboyo Member

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    give the boy a back hander to pass it ...problem fixed:cool:
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  16. Welly
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    Welly VX220 SC Driver :)

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    I hear that I must admit - but it won't be helping fuel economy. Ultimately the money you spend now you will save in fuel over a period of time....
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  17. s3jack
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    s3jack New Member

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    I did think about seeing if he would accept a back hander but then thought if its on its way out may as well get it replaced :)

    1 last question, would a lambda sensor from a similar year 225 audi tt be a straight swap for mine? as funny enough my uncles friend bought a new sensor as he thought his was on his way out but it ended up being another fault with the car, so he has a brand new sensor there and said i could have it for £30:icon_thumright: as far as im aware they are the same engines?

    cheers
    #17
  18. finesse
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    finesse Active Member

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    Taken to a mechanic, how many hours work?
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  19. Welly
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    Welly VX220 SC Driver :)

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    It took me about 15 mins to re-wire the lambda. About an hour and a half all together, including removing charge pipe assembly to get to the lambda, and then refit.

    It's not a hard job. This is for the first lambda on the downpipe.
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  20. S3KO4
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    S3KO4 Member

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    If it is related to blue smoke from the car, I added a stop smoke liquid to the old oil and it passed through.. I blamed Santa Pod excitement.
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