Catalytic converter

I've got a 2006 4-cyl Tacoma with 212,000 miles that supposedly has a bad catalytic converter (a mechanic shop told me when I bought it, but I didn't think to ask how they could tell). Is there a way to tell if it needs replaced, or if it's just the O2 sensor/s?

The most in-depth repair I've ever done is replace brake pads (in other words, assume I know nothing).

If I do need to replace the catalytic converter/s, what should I buy to get the best bang for my buck? I have a friend who can weld if necessary, but I'd like to do it myself even if it costs a bit more.

 

Dummy cat depending where you are located and emissions standards... have your buddy weld it up! If a exhaust shop says it's bad and it's a reputable place ... it's prolly bad, they get them on regular basis (hope your not at a national chain shop... they will penny pinch left and right!).

 

Wouldn't that cause problems for emissions testing?

 

Like I said, some states don't have any, don't know where op is located... but yes it can lol