My 2012 Twinair just failed it's MOT due to above the limit lambda readings , the co and hc were fine...just the last part.
What could this be down to? Faulty Lambda sensor???

quotethepigeon said:

My 2012 Twinair just failed it's MOT due to above the limit lambda readings , the co and hc were fine...just the last part.
What could this be down to? Faulty Lambda sensor???

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Didn't have the VW software turned on :devil:

Meeeeow! Lol

The MOT testing equipment has detected more than the allowed O2 content on the exhaust gases. (limit is 1.03 or very near methinks)

There are a few reasons for this, but my first point to check would be leaks, both intake side and exhaust side.

But due to the HC and CO being normal, I would edge a bet being an exhaust leak.
It doesn't take much to push it over, a little pin hole in the flexy, small manifold crack or the an exhaust manifold gasket split would do it.

Goudrons said:

The MOT testing equipment has detected more than the allowed O2 content on the exhaust gases. (limit is 1.03 or very near methinks)

There are a few reasons for this, but my first point to check would be leaks, both intake side and exhaust side.

But due to the HC and CO being normal, I would edge a bet being an exhaust leak.
It doesn't take much to push it over, a little pin hole in the flexy, small manifold crack or the an exhaust manifold gasket split would do it.

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I need to phrase this carefully, but it's not entirely unknown for a testing centre to 'cheat' to give them a reason to sell you a repair. This actually happened to a friend of mine; they failed a car on emissions and charged an extra £180 to replace a lambda sensor. As far as I could tell, the results were no different after they'd fitted the new one and it was out of limits when retested, but they reran the test and pronounced it within limits. I've heard it said that not fully inserting the testing probe can produce a similar result, as can allowing the car to cool down before testing.

If you google "MOT emissions lambda scam", the results make interesting reading.

I'm not saying that's the case here; many cars are legitimately failed on emissions; exhausts can leak, and lambda sensors can go out of tolerance.

cheers guys , my mates gonna have a look at it in his workshop. Will see what he says !

I'll keep you posted ..... If anyone is gonna get mugged off its me lol

Seems unusual for a 2012 car, you could always chance your arm and bring it back for the retest and see what happens before doing anything

reckon it's worth just getting an emissions test elsewhere?

quotethepigeon said:

cheers guys , my mates gonna have a look at it in his workshop. Will see what he says !

I'll keep you posted ..... If anyone is gonna get mugged off its me lol

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what are the actual figures..,
had my Punto TA tested the other week,
figures were still VERY low :worship: = 22K miles and oil half degraded

Charlie

here......I think I've attached it???

Here's mine from last week for comparison.

I see apart from your fail, my figures are higher.

Don't do anything else till you change airfilter or have it serviced. Any emissions fail ive ever had has been cured by that action.

Mind that said I dont think they were lambda measurements...

I wonder, does the TA have this new "drain" in it's silencer/exhaust like the 1.2's are reported to have?

ExBluebird said:

Don't do anything else till you change airfilter or have it serviced. Any emissions fail ive ever had has been cured by that action.

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Changing the air filter is most unlikely to affect the lambda readings. It's a common misconception, but on a modern, electronically controlled car, a blocked air filter will have no effect whatsoever on performance except at wide open throttle - the electronics will adjust the fuelling according to the amount of air that's available. It's still important to change them, but that's primarily to stop dirt from getting into the engine and causing extra wear.

Goudrons said:

I wonder, does the TA have this new "drain" in it's silencer/exhaust like the 1.2's are reported to have?

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You'll find a tiny drain hole in most modern silencers; the exhaust system should be under positive pressure when the engine is running and I don't think this could be influencing the result.

It's possible the lambda sensor may have failed; most likely the upstream one. Note the two sensors on the 312A2.000 engine are different, so you can't just swap them round.

This is the correct replacement for the upstream sensor on the 0.9TA. Not cheap, but for DIY types, changing one 'blind' is worth it if it fixes the problem. Due to heat & corrosion, they can sometimes be a pig to remove. You can buy a special socket with a cutout to clear the wiring, but if you're scrapping the old one, just cut the wires off!

Re the MOT emissions scam, that's why I now take my cars to a local MOT testing station in Lowestoft that doesn't do repairs. They have no interest in failing a car just to generate work, and they are lovely people to deal with. Every year I get the same joke about the Barchetta, which is that they think it should fail because the steering wheel's been fitted on the wrong side. An oldie, but a goodie.

gar074 said:

Every year I get the same joke about the Barchetta, which is that they think it should fail because the steering wheel's been fitted on the wrong side. An oldie, but a goodie.

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Next year, make sure they MOT it using a left-handed testing bay

jrkitching said:

I need to phrase this carefully, but it's not entirely unknown for a testing centre to 'cheat' to give them a reason to sell you a repair. This actually happened to a friend of mine; they failed a car on emissions and charged an extra £180 to replace a lambda sensor. As far as I could tell, the results were no different after they'd fitted the new one and it was out of limits when retested, but they reran the test and pronounced it within limits. I've heard it said that not fully inserting the testing probe can produce a similar result, as can allowing the car to cool down before testing.

If you google "MOT emissions lambda scam", the results make interesting reading.

I'm not saying that's the case here; many cars are legitimately failed on emissions; exhausts can leak, and lambda sensors can go out of tolerance.

Click to expand...

I agree, it's probably a leak if genuine, or the probe not in enough. The twin cylinders could be causing a lot of pulsing in the exhaust which can cause air to be drawn back up the pipe, reaching the probe, causing an excesive O2 reading.
I had the same problem on my Dodge V8 but the MOT station did everything they could to get it right. They said it was caused by the lumpy exhaust pulses of the V8 drawing air back up the exhaust. They fixed the problem by putting rags up one of the twin tailpipes, which stopped air being drawn into the system, as they had already checked it for leaks.
It's just a guess that this might be happening with the lumpy exhaust pulses of the twin cylinders.

My mate took it to his garage , failed on the emissions again. Hooked it up , cleared some codes and it passed..... For future reference I'm thinking I could have done this on multiscan....

Our 2013 is getting tested tomorrow..
On the way back from a 14 mile commute

Will post the findings