Permanent P0420 - Catalyst System Efficiency Below Threshold
 

Code P0420 popped up about 4 months ago after I got an oil change from Nissan. They cleared the code and the CEL stayed off until this morning. The only thing I did over the past couple days was clean the air filters on the Stillen long tube CAI. I cleared the code so that the CEL would turn off but the P0420 is showing up as a permanent code on the OBD scanner.

I have Berk HFCs installed. Could it be the HFC is going bad or maybe the O2 sensor?

Other upgrades:
Stillen exhaust
Motordyne manifold
UPRev Tune

All bolt-ons and tune were installed about 13,000 miles ago and I've never had a problem with this code or any other code prior to the oil change 4 months ago.

You could be running a little rich. Or, your cat for the specified bank that code is related to is toast. It could also be that the down stream O2 sensor is skewed. You would need to test the sensor or view the PID on the computer if the generic ones can do that.

Also, the permanent code is not permanent as in it will never go away. I've noticed here at Ford some DTC's that are "permanent" don't go away when you run a KOEO test unless the vehicle has gone through a drive cycle and the issue is fixed. If the issue is fixed the code doesn't show up as "permananet" no more when you run a KOEO test.

Could you specify what exactly that code is. Sounds like your talking about a cat code. If you have high flow cats and no tune there is a good chance you will throw a cel. When I had my HFC nothing would keep the CEL off until I had the car tuned and the CEL deleted.

Last month I got a PO430. Its for the other bank. I was running Berk HFCs I had bought used so I just bought a new set and that cleared it.

Never had a problem with the Berks and codes before that...either before or after tuning.

I think berk does a good job at keeping the code off, I actually had berk HFC when I bought my car without knowing. Had the code come pop up one time and I cleared it and it never returned. When I went to buy HFC( because I never knew I had them on my car in the first place) I replaced them with Z1 brand and it threw a code within 15 minutes and would not go away without a tune. I later found out I had berks on my car when trying to sell what I thought was a stock cat lol

I really do not want to spend the money on new HFCs to troubleshoot this problem. I think this may be an O2 sensor issue. I say this because the permanent P0420 went away after a day. Codes P0430 and P0420 came up last weekend. So supposedly both HFCs are operating below the threshold, but once again, the codes went away after a day.

I assume if the HFCs were going bad the codes would always be there.

P0420 is Catalyst System Efficiency Below Threshold (bank 1). Just by looking at the code description you would think it's a cat converter problem but the possible problems are:

Faulty catalytic converter
Engine misfire
Fuel injector leaking
Engine mechanical damage
Oxygen sensor that has improper readings
Exhaust leak

I think it's an oxygen senor issue since the code comes and goes after a day. I do have HFCs with a tune. This code first came up after about 12,000 miles after the HFC install. I actually went a couple months after the HFC install before I got the tune and I didn't have any CELs.

I will test the O2 sensors soon and see how that goes.

How would you test the o^2 sensor? I’m getting this P0420 in my 2012 for about 24 hours now. Thanks for any reply