Emissions problem.

E39 528. Has now passed all the MOT tests, bar the 'Natural Idle Test' CO level at 2000 revs is a Pass, and Lamda is also a Pass. The last item on the test sheet is simply CO Level 0.85 %, which is also a Fail. I assume
this just refers to the Natural Idle Test.
Failed on the same points the first time, so on the advice of the tester and the garage that did the work on the brakes etc, I bought 1 new Lamda sensor which the garage fitted today. It made no difference, so the 2nd sensor was changed for the one that had been removed, on the basis that if it wasn't any different to the new one, it might be the 2nd sensor that was faulty. Still no difference. It would appear that both Lamdas are OK. but CO levels are still too high a tickover I'm going to have a diagnostic check done by my local BMW dealer, who hopefully will be able to pinpoint the fault, but in the meantime has anyone any suggestions of what might be causing the high CO reading at tickover? TIA. Mike.
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Get your local dealer to check the fault memory. Alternatively, how far do you live from your MOT station? Are you close?
I have had vehicles fail the MOT on emissions tests, but the next time I look it there (without changing anything) it passed! I didn't change anything, I just got it hot first by a decent run, and it passed! In the trade, it's referred to an Italian de-coke! But obviously observe the speed limits!

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Was it fully warmed up? Does the test report give the oil temperature? I've only attended one test on mine at a station some 3 miles away, and they spent ages warming the engine at fast idle before they'd even conduct the tests.
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Dave Plowman snipped-for-privacy@davenoise.co.uk London SW
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wrote:

The garage that did the brakes etc, took it for the MOT which was about 3 miles away, so it should have been reasonably warm when it got there. But the notes on the test sheet say:- 'Engine speed measurement by-passed' 'Engine oil temperature by-passed - Cooling fan cut-in'
I would assume if the cooling fan cut in that the engine was fully up to temperature, but you have a point. I'll see what the local BMW dealer wants for a full diagnostic check, and if it's pricey, it might be worth booking another test, then thrashing it for a few miles immediately before it's tested. Give it an Italian tuneup as they say. :-) Mike.
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Mine said that on one test - with the aux fan not working. ;-)
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Dave Plowman snipped-for-privacy@davenoise.co.uk London SW
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