Thread: P0420 code, car runs sometimes, then stops

My wife has a 2002 Grand Prix 3.1 V6 that we have been having some problems with. It died(luckily) right next to an Advanced Auto parts store so I had my brother tow me into the parking lot. As soon as that happened it started again. Weird. I ran the free diagnostic at Advanced and came up with a P0420 code. The guy there said O2 sensors...so we replaced. Still same problem. Car will start and run sometimes, but then sometimes wont start. I thought that p0420 was possibly Cat(exhaust seems to be pushing fine and no smell), but didnt think it would cause this issue. Also when it was dead and I tried to start the security light came on. Sorry if this is a double question but I am at a loss and have little money to take into a GM dealer. Any thoughts are welcome.

Thanks

Well, it could quite possibly be the CAT, is the code still active though? If it comes back, you may need to replace the converter.

Yeah Ill have to take it back up there when I can get it running to check if the code is still there. I just never thought a Cat could cause these types of problems. Thanks for the response!

depending on your states emmision laws hollow the think out instead of replacing it and spend the money on a tune to remove teh second o2 sensor