Just put my Volvo 850 through an MOT and it passed with flying colours (hurray!)
Unfortunately, the Lambda light is now lit (it wasn't before).
I have informed my usual garage about the problem (they sub-contracted the MOT) and they said that they will look into it.
Any ideas what may have happened - is it serious? Should I still be driving it while it's investigated?
Many thanks for suggestions.
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Hi N. Some months ago, the lambda warning light on my 940 came on for no apparent reason and stayed on. I took it to the dealer who read the fault code, cleaned the lambda probe and reset the light. It was all done in 20 mins. while I waited and only cost £35 IIRC.
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Funnily enough (well not that funny because it cost me £115) but my engine light came on 1 mile after an MOT. After checking the ECU fault code , it turned out to be the Lambda Sensor.
This was on a Cavalier, but I guess the principle is the same - I can only guess that the sustained engine speed on the emission test must have finished-off the sensor - it was in quite a sorry state when I removed it - had to change it because no amount of soaking could revive it...
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Forgot to say that the car was considerably quicker without the Lambda Sensor input - richer mixture I guess, but of course, if you leave it , your CAT won't survive for very long...
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When mine went the lambda probe was cleaned and the system reset. I was a tad worried about the state of the emissions but the car has just passed its MOT and they were fine. IIRC the guy in the garage said it's quite common for the lambda sensor to play up and cleaning often did the trick. So far so good - touch wood!
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How should you go about cleaning a lambda sensor? Mine is getting lazy on my 1.4 corsa-its a single wire unit. Also is it true you need to use special grease when re-ftting? Would copper grease do?
Thanks guys for all your help
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How on earth do you get them out? When I tried once I found it so tight I realised that if I applied any more torque the whole body would be twisted apart, or that the cat would collapse first.
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Yes you should use special grease on the threads of an O2 sensor. This has small glass beads in it, and if you don't use it you'll have a hell of a problem removing it again at a later date.
The easiest way to clean the sensor is to blast the car up the road. There's no such thing as a lazy sensor, (or a lazy starter motor for the matter).
Oxygen sensors contain zirconia which is sensitive to oxygen. They become contaminated with carbon over time, especially if the car is only used for short trips. Once covered in carbon the sensor gives the ECU an inaccurate reading of oxygen. This leads the ECU to think that the mixture is too lean, as so richens up. Richer mixture means more carbon, and more carbon means more inaccuracy, and that means richer mixture etc. etc. etc.
So go for a good drive, get the engine hot, and thrash it a bit to blow out all the excess carbon from the exhaust.
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Hi Gang - on re-reading this thread I've just realised my mistake, so apologies for the confusion.
The lambda warning light on my 940 came on and was diagnosed as an MAF sensor fault. It was this that was cleaned and replaced - NOT the lambda probe !
IIRC someone here kindly told me that the lambda warning light is really an engine management warning light which could indicated any one of a number of problems. In my case the fault codes indicated an MAF problem.
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