Hi all, my S4 TT has just failed MOT on emissions (which have never been a problem before). Before the test I went for a 60 mile blat up the motorway so she was nice and warm, but the CO reading was 3.9 - yes that decimal point is in the right place, the allowable limit is 0.2!

 

Having a search through previous posts I tried disconnecting the two hoses by the balance tube, one at a time, and that dropped the reading to 2.0 but still 10x the limit. Sadly my car is just new enough that it has to have a post-Cat test not Basic Emissions.

 

Just looking for suggestions on what to try next. I’ve got a new air filter arriving tomorrow and have found the instructions on how to check the ECU for lambda sensor error codes. The idle when warmed up is rock solid at about 900 with air con off in current temperatures, and the lambda reading on the MOT was borderline but ok.

 

It has crossed my mind that previous testers may have assumed it had no cat, so the “try another garage” option is already on the table!

 

Thanks for any ideas

 

Chris

Disconnected it runs directly from the fuel map without 'correcting'. Many people unplug them you should be fine.

Even on a cat test? Worth a try anyway, thanks. I spoke to Jimmer and he suggested unplugging too so it must be good advice!

After unplugging he sensor, I would also unplug the battery for a few hours to reset the ECU.

Thanks Alic, I hadn’t considered it might have memory. I hate that my car is probably smarter than me.

Sensors disconnected this morning, battery off for an hour or two, reconnected and running smoothly. Will go for a couple of long runs and get booked back in for another test. Fingers crossed!

Sensors disconnected this morning, battery off for an hour or two, reconnected and running smoothly. Will go for a couple of long runs and get booked back in for another test. Fingers crossed!

Ask the man nicely and he may do a test on the emissions machine to see if it will pass before he logs on for a retest. We do this to help our customers.

 

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Thanks Chris, I know a place where I can get that done. If it doesn’t get through I can then try it with the AIV solenoid hose disconnected, that definitely cut down the CO last time

But it serves no purpose to show it has been previously tested to us. If one VTS fails your car you can drive to another and get a pass.

 

If the system automatically showed us it had just failed then testers would be unfairly looking at those previous fail items.

 

Every test must be carried out using the testers own view of the vehicle not someone elses.

 

Only when testing the vehicle at the same VTS will it show as a re test (if it meets criteria for a re test).

 

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That makes perfect sense Chris....:thumbup:

 

Ask the man nicely and he may do a test on the emissions machine to see if it will pass before he logs on for a retest. We do this to help our customers.

 

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....And sound advice there...:cool:

After a week of driving with the lambda sensors disconnected I went for an emissions test again today. CO was around 0.12 or less, HC was almost non existent, but lambda was zero. Zero. It only appeared at all on the overrun, when it briefly went to 1.12, then back to zero.

 

My initial thought was the tester was duff, but I queried and mine wasn’t the first MOT that day so unless it had failed that minute it seems unlikely. Is zero lambda even possible?!?!

 

So I’ve reconnected the LH sensor, which read out OK, and disconnected the battery to reset the ECU and will go for a long drive tonight. Last chance test tomorrow when the MOT actually runs out, after which whatever the result I think it’s time for a visit to Uncle Jimmer!

Edited November 10, 20178 yr by Scarecrow