MOT fail, high Lambda. Please Help

anno888 · Post by **anno888** » 19 Jan 2005, 23:01

Hi all,
I took my Xantia for its retest and it failed the MOT due to the Lambda reading being too high.
Since its first test I changed the spark plugs, oil, air and oil filter as advised.
The tester said that the Cat seems OK but that the car is due for a new back box as there is a rattle from it. He also said that it could be the Lambda sensor but he wouldn't be sure untill he changed either one. He also said that mixture sould be fine as the other emmision tests (CO level and HC level)are ok.
My question is, what is more likely to be the cause of a high Lambda reading, back box or faulty sensor??
I don't want to have to change both at ths stage if only one is the cause.
How much should I expect to pay for replacing the Lambda sensor?

turbolag · Post by **turbolag** » 20 Jan 2005, 00:41

Is it the '93 Xantia mentioned in your sig? Reason i ask is that all petrol cars from 1st aug 1992 are required to have a cat for the MOT, but not all are required to have the cat test. There are numerous exemptions to the cat test(from my Nissan spannering days, all Primeras to chassis no 380000, or about mid '94, for example) and there is a good chance yours shouldn't be having the cat test at all at that age. Check with a citroen stealer with an MOT test station and they should be able to advise as a non franchise MOT outlet will get hundreds of ministry bulletins a year detailing quirks and exemptions, and it's impossible to keep abreast of them all.
Good luck, hope it gets sorted.

anno888 · Post by **anno888** » 20 Jan 2005, 01:16

Yes, it is the 93' 2.0 SX.
So, what I think you are suggesting is that due to the age of my car it is required to have a cat fitted for MOT but the cat is not required to be tested. Does that mean that no emmision test is done at all? Hence no Lambda measurement??
I will try to call a Cit dealer with MOT test station to find out. Will save me a good deal of cash if this is infact the case.
Cheers

Post by **RichardW** » 20 Jan 2005, 01:58

My Dad's 93 1.8 failed its first MOT on high lambda. There were mutterings about lambda sensors, new ECU, new cat etc etc. In the end the garage took the ECU and replaced it with another one and it passed. They then put the old one back in and it still passed! Conclusion there was a bit of corrosion on the connector causing the signal from the lambda sensor to be out. Might be worth a try taking the ECU out and cleaning the contacts.