Does the Cat need to work in order to pass the MOT?

[mat_fenwick]

I'm not sure how, but my 1996 Discovery (fitted with two cats from new) has just passed the MOT, tested against the non-cat emissions standards! I thought the standards to test against are automatically chosen from the MOT database, to prevent testers being able to push non compliant vehicles through a more lenient test?

[Gilbertd]

When the tester starts the test, he enters the VRN and the next screen asks what fuel the car is running on. Select petrol and it starts the cat test, select LPG and it starts the non-cat test. You can check the MoT history of a car on the VOSA website and it will tell you what fuel it was tested on for each test it has had in the past. My LSE has been tested on LPG since I've owned it but on petrol a few times in the past.

[Nick0070]

I've been looking for a replacement exhaust for Mk 4 fiesta 1.25 zetec, supplier of a four branch (cat less) manifold,middle pipe (no box) and rear box state that the system is both road legal and suitable for MOT!

[Gilbertd]

It was up until 1 January this year. There are a number of alterations to the test that came into force on that date and one is that a car that had a cat fitted when new will fail if it doesn't have a cat fitted when taken for test.

[PhilMcConnachie]

If the test had been done correctly, it would have been warmed up before being tested so would have switched over. If it was tested on petrol and failed on emisions, it's because it was not tested correctly because it wasn't tested with a hot engine. In the same way that the regulations are quite specific, if the car was originally fitted with a cat, it will fail the test if it has been removed. This is irrespective of what fuel it is running on and whether or not it fails the emissions test. In fact, I would say that any tester that is doing the test by the book, wouldn't even test the emissions if there is no cat as it has already failed.

Mine has a cat but when you hit it with your fist it just rattles around so i think the filter inside is bust. So, it looks like it has a cat I suppose.

Thing is, after starting from cold, you have to give it some gas to get it to switch to lpg otherwise it just keeps running on petrol. If the tester just drove it on to the ramp and waited for it to get warm , it would still be running on petrol indefinitely unless he hit the accelerator to make it switch fuel.

[Gilbertd]

So tell him then. Drive it in on gas, tell him it runs on gas and that he has to give it some revs to switch over. Or, assuming a single point, set it to start on gas. If you leave it rather than having it done while you wait and come back to be told that it has failed on emissions, check the printout. If it shows a lambda reading, it's been tested to the petrol standard. The non-cat test will only show CO and HC figures.

[garys]

just to let you know my experience. my sons corsa c fitted with lpg had a blocked cat that we drilled out. when it needed an MOT we were advised to make sure the car was fully warmed up. It passed

[reggieroo]

That's good to know garys, thanks.