hi, just wondering if anyone knows what it actually does and if this could be causing my r33 to run really rich as my cat sensor doesnt work. does not show any resistance no matter how hot or cold cat is.Should i bother replacing it as they are expensive little things. thanks deano

it is a temperature sensor. when it shorts out you will get a light come on the dash saying that the exhaust gas is too hot. shouldn't have any affect on fuel mixtures.

Nope no need to replace it. Its useless really. Its only an indication telling you that you have high temps in the cat which could damage it.

When I had the std compliance cat car had water in coilpacks (dont ask how) excess fuel was being dumped into the car and burnt off. The light would go off.

Then cat was replaced and couldnt fit the temp sensor so it was grounded to stop the light being on.