Faulty Catalytic Converter - Signs

Don't know about sound or driving differently, most obvious sign of a failing cat is increased emissions. You could get the exhaust gases analysed and compare them to the readings at the last MOT.

If your Lambda sensor was faulty, you may get an Engine warning light on your dashboard. A faulty sensor could cause the engine management system to richen the mixture in order to "get you home". This would slowly kill off the cat by drowning it in oil

If your car is belching out oily smoke, then your cat is most certainly dead, although this is probably caused by a fault in the engine- the cat is just a casualty.

I had a cat fail because of a broken lamda sensor. Didn't notice any difference in performance, other than increased oil consumption. Noticed when it came to the repair bill though!!!

Hope this is of some help.

Craig

Depends how it's failed.

The core can break up, which can cause a rattle sound, and/or lack of power due to the core restricting exhaust gas flow. The core can melt, which would also cause lack of power. Or the catalytic coating can be washed off, leading to increased emmissions.

I had a new EGR valve fitted about three weeks ago could that have caused it>

I had a new EGR valve fitted about three weeks ago, because of warning light and mis-firing could that have caused it?

Hesitation and car feeling lethargic. Rattle when knocking on side of CAT.

As others have said, maybe nothing through to feeling sluggish.

Typically it doesn't feel any different to most drivers.