Quick question for anyone who know about cars, if the exhaust system has a major leak of gasses could it be caused by the catalytic converter? This is also assuming that the emissions are all within the guidelines.

No, but if the cat is in a separate section, then there could be a leak in the gaskets (join) between the exhaust sections.

Some leaks can be 'fixed' with exahust putty at very low cost alowing the car to last perhaps until the next mot.

Ok, does it sound reasonable that if I the car failed the MOT on a major leak of gasses in the exhaust system that the cat would need replacing, as that is what I was told? It didn't fail the emissions test.

Thanks for the reply by the way

They should be able to tell you where it's leaking. Might just be the exhaust is cracked somewhere?

Don't think I explained very well! My car failed its MOT on the Exhaust system having a major leak of gasses and they have said it needs the cat replacing. My limited knowledge of all things car related meant that didn't make sense. I asked them to explain, but wanted to avoid them thinking I was accusing them of been on the fiddle when I still didn't understand.

I thought if there was a leak that usually meant the exhaust was cracked. If the cat was faulty I thought that would mean the emissions were too high. So to me the reason it failed and the the bit that needs replacing doesn't make sense, just wanted some clarification from anyone who knows a little more than me.

go to www.carmechanicsmag.co.uk
Log in as a member, and have a look at the forum section, ask there and you'll quickly have an answer. I use it and the people on there are really helpful!

If the cat had disintegrated/partially disintegrated, or just wasnt doing its thing any longer, then your car would fail on too high emissions.

If there is a leak, then there is a leak. To me, a leak doesnt suggest the cat needs replacing, just that the leak needs fixing... but I'm no mechanic.

*however* if the leak is in the section of the exhaust where the cat is - perhaps its the entire front section from the manifold - and the section is in such a state that it cant be repaired, then perhaps they are replacing this and it just happens to contain the cat. But the mechanic perhaps just explained to you that they were replacing the cat as its easier for people to understand (and people associate cats as £££ too).

Well after the weekend I understand all this a lot better. Went for a drive in the country and came back attached to a tow truck! The front bit of the exhaust dropped off including the cat.

Try the lamba sensor or the cat...what year is it?

Too late now. The whole thing was rotten anyway so I have a new one fitted now.

I love it when I'm right :clap: :P :D

How much then? Did you replace the whole exhaust? Stats of car - type/age/mileage etc (just caus I'm anal and like to know these details :)