How do I know if catalytic converter is bad on my truck?

If you fail the smog test, it could be burned out.

If you have decreased performance, it could be plugged up.

A severly plugged up one will get very hot and even glow if it gets hot enough.

if the truck runs good and you fail the emission test then the easy way to check the catalytic converter is to get and oven temperature gauge and run the truck at high idle 1200 rpm for two minutes to make sure the truck is warm up, then use the gauge at the front of the cat and at the back of the cat, the back of the cat should be 100 degree or more then the front. ( the front of the cat is the closes to the engine) If the temperature is the same then the cat is not working ( may need more info if the truck has a air pump for the emission.

it will smell really bad......or if you look under your car and there are holes rusted through, it will need replaced.......it is located right after the headers connectiong to the rest of your exhaust going back......I don't know why you have this idea but if your check engine light is on it may very well just be an O2 sensor......if your car fails E-check that is another sign of a bad converter....you can also call around and usually you can find a place to inspect it for free...but beware make sure you trust the mechanic...because some just want to get rich by fixing the unescesary this is why I have been learning about cars.......

It will smell like rotten eggs, you may hear what sounds to be a rattling under your car, which would be the ceramic inside the converter rattling, and most likely your check engine light will be on because for cat efficiency or an O2 code..

to check for backpressure-clogged cat drill a hole in the exhaust pipe before the converter, put a pressure gauge on the hole with the engine running anything over 3 psi you have a clogged cat.dont let people tell you cats are expensive we only pay 25 dollars for them wholesale.

Usually the truck wont run well or stall out if it is. THe best thing you can do is take it to a muffler shop and have them check it out.

The smell will be like rotten eggs.

normally a bad rotten egg smells when they are going out.