Code P0420

[BlackJack]

My check engine light came on and stayed on today after multiple cycles. I took the car to Autozone to have the codes checked and he came up with code P0420 Catalyst efficiency low bank 1.
Possible causes
1) Catalytic Converter defective(Failure possibly due to #2, #3, or #4). Catalytic converter is not glowing and exhaust comes out both tips.
2)Engine mis-fire or running condition.
3)Large vacuum leak
4)Engine oil leakage into exhaust-valve guide seals, piston rings.

I have done a search on this forum and have done a cursory look see at the vacuum lines but I will get more into it tomorrow.

It has a Trans-Dapt EFI spacer on it. Not sure if it matters. I think it has a stock tune but there is a remnant of a SCT tag on the fuse box in the engine compartment. The speedometer reads about 5 mph slow compared to my GPS and the tach barely moves when revved but mostly stays at zero. I rinsed off the engine at the coin op wash yesterday but didn't pull the trigger and the engine was running. It still runs very well though and has 107k miles. I just traded for this car Wednesday so I don't really know any history except for what's on the CarFax report.The dealer said they had a check engine light and they replaced an O2 sensor.The car has an Autometer digital A/F guage that seems to be hunting all around quite a bit but I have no idea if this is normal. This is about as thorough as I can be.

If I find the problem will the Check Engine light go out on its own or will the codes have to be cleared? Any help would be appreciated.

[Mike M]

It has a bad cat on bank 1

[FF1077]

I had the same code and it turned out to be a exhaust leak at the collector.

[BlackJack]

I will check out those leads guys. Thanks!

[BlackJack]

I had the rear cat replaced on the passenger side. It was completely hollow. Hopefully that fixed 'er. No "check engine" light so far.

[yjmud]

the rear cats are not monitored
unfortunately the light WILL come back on

[Mike M]

the rear cats are not monitored
unfortunately the light WILL come back on

Yep, 420 has to be a front cat. You can take off both rear cats and your check eng light won't come on (assuming your frt cats are working).

[BlackJack]

That bit of info would have been helpful a couple of days ago because I basically threw that money away. Now I have to get a front cat because the light came on again after 35 miles. I'll get it done ASAP.

[screamn]

I had the rear cat replaced on the passenger side. It was completely hollow. Hopefully that fixed 'er. No "check engine" light so far.

On a different note, the previous owner(s) possibly hollowed out the rear cats instead of taking them off in an effort to avoid any issues during emission inspections.

[yjmud]

That bit of info would have been helpful a couple of days ago because I basically threw that money away. Now I have to get a front cat because the light came on again after 35 miles. I'll get it done ASAP.

my crystal ball is broken, now referring to magic 8 ball

[BlackJack]

I should not be critical when asking for help and for that I apologize. It's just that I got a helpful comment that I had a bad cat then after the replacement told that I don't need to worry about the rear cats.
The shop should get the front cat shipped in Monday although it might be next weekend before I can get it installed. It is cheaper than the rear cat. I shall report back when the repair is made in case someone uses this as a reference thread to help their problem.