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[scott sp1]

can anyone help?? i've got a 2000 2.2 automatic omega with the fault code p0420 cat efficiency low bank 1.  I replaced the standard cat with an after market one and had both o2 sensors replaced but yet the eml keeps coming on and reading the same fault code.  I even tried taking back the after market cat and getting it replaced under warrenty thinking it might be a faulty unit but still the light comes back on after resetting.  has anyone had a similar problem and should I be looking for something else i.e. vaccum leeks or airflow sensor fault etc.  Any help would be greatly appreciated, thanks!!

[Albatross]

Your car is one of the new ones with pre-cats so you may be suffering from the same root cause problem as many of us on here who have the 2.6 and 3.2 litre V6 cars.

It is related to the lambda sensors before and after the pre-cats which send a message back to an over sensitively programmed ECU.

There is a solution which works on the V6 and you may want to consider trying it on your car.

This comes up regularly (at least every couple of weeks) and was posted up only earleir today. Have a look at this thread:

http://www.omegaowners.com/forum/YaBB.pl?num=1212591581

[scott sp1]

i understand how that would work on that system!!but dont think it would work on mine!!my after market cat only has one cat and o2 sensor before and after.i noticed that the old one has two cats!i brought this up with the suplier and they said thats the only exhaust listed for my car!!could it be the missing pre cat thats causing my problem with this fault code!! :-/ if i bought a vauxhall cat will it have a pre cat on it and what would be the cost,not cheap i'll bet? and will this sort my problem ive also had the emmissions checked and they passed all tests!!ohhh why is this light on ohh why once again thank  you for any help on this matter!!!!

[Albatross]

Put your old exhaust/cat back on. If this diagnosis is the problem then there may well be nothing wrong with your old system.

Once you've got your old system back on then try the solution outlined. By putting the aftermarket kit on youre only making the roblem more difficult to resolve.

There is only an assumption that the old cat was at fault in the 1st place.

[bigall]

Any other fault code as well as p0420 - was the code obtained using a tech2?

I ask because when I had that problem another code stored indicated egr valve malfunction. The technician cleared them both and sent me away until the management light came on then read them again in order to find the order of code in order to find offending item/s In my case both egr and sensor were knackered - both changed no more light