Fail MOT on Oxygen Reading

[h31met]

Can any one help. I have just tryed to mot my legnum and the computer has failed it on the oxyen reading. The bloke who did the test is not to sure what the problem is so i am a little stuck. CO2 if very low and so is the hydro thing but the oxyen is to high. Has any one had this and knows what to change to get it right and where and how much for the part thanks.

[Kieran]

Oxygen too high? you mean the 02/Lambda reading?

Sounds like a weak mixture? Could be lots of things. Does the car drive okay, what's the fuel consumption like, etc.?

[h31met]

Oxygen too high? you mean the 02/Lambda reading?

Sounds like a weak mixture? Could be lots of things. Does the car drive okay, what's the fuel consumption like, etc.?
car runs fine fuel is ok taking it easy car get about 300 miles out of a tank

[TAR]

if it has a high Lambda and high 02 (0.5 to 1.5%), the CAT could be faulty. Before condemning it make sure its hot enough to work, the Lambda and other sensors are working OK and the exhaust downpipe hasn't got any leaks.

if the Lambda fails then...if its too high the Lambda sensor may be faulty, the mixture may be too weak or there may be a hole in the exhaust downpipe. If Lambda is too low the sensor may be faulty, the mixture may be rich or the vehicle may be misfiring.


Make sure the car is nice and hot before the MOT test, the CAT needs to be hot to work efficiently.

[orionn2o]

Yes heat is your friend on this test! The Cat MUST be hot, otehrwise it will fail.

I had problems at the other end of the spectrum ie too much CO2 and hydrocarbons. So unfortunately I don't have experience with your problem . :(