So my car came up with an SES light the other day. Got home and checked it and scanner showed one code as p0420 which is catalytic converter not working efficiently or something like that. I searched but I got a lot of mixed answers.

How do I know if my cat is bad? Anyway to check for sure?

Could it be an o2 sensor?

My car seems to be running fine I'm averaging 20.4mpg mixed driving. Any help is appreciated thanks.

 

If you're still getting that mileage, its not likely going to be your O2 sensor. Bad O2 sensors usually cut you mileage significantly (like by half). It is probably your cat, like it says. Its probably partially clogged. Our cars are getting to that age where stock cats can start goin.

Here's the thing tho, if its a bad cat and you don't get it fixed it will drag your O2 sensors and other smog parts down with it and be a much more costly repair than just replacing the cat. Get it taken care of asap. You don't wanna mess with these.

 

Do you have anything done to the car?

 

i had a bad o2 sensor (upstream passenger side) and mileage was never affected...

 

Thanks for the replies.

No the car is completely stock. Is there any way to check if its for sure the cat before I start throwing $$$ at this thing?

 

Also say its Bank 1. Is that driver or passenger side?

Also would it be the o2 sensor before the cat or after?on which side?

 

clear the code and see if it comes back. could be a glitch.

 

The night the code popped up I cleared it. Then next morning it came back up like after 10miles I cleared it again to see if it might be a ghost code or whatever

 

Either the cat is failing, or you have an exhaust leak (blown out gasket etc) or the sensor is fried. It would be the secondary O2 sensor in the cat that was the problem. If the primary O2 sensor thats up in the header failed you would have a lot more codes than just the 420

 

Secondary o2 is after the cat? Is there anyway to tell for sure which one is bad the sensor or cat?

 

swap the sensors left to right and see if the code changes. if the code moves with the sensor then its the sensor. if you swap sensors and the code stays the same its something else

 

Will do those o2s are behind the cat right?towards the rear?

 

yes they are the sensors closest to the rear

 

So I've drove it about 20miles and the code hasn't came back. I'm a little surprised.

Haven't swapped out sensors though waiting for the code to pop up. If for whatever reason its the cat can I just go to a muffler shop and get a aftermarket put on?

 

You most likely will be able to get a universal cat at a muffler shop, yes, but they're pieces of crap. I know the OEM ones are expensive as *****, but they last a long long time.

Or you can try the kinetix HFC. Those seem to pass Cali smog laws. You can order them from conceptzperformance.com