Had this CEL thrown a couple times now. Cleared and it comes back every couple days over the last couple weeks. Showed up after a AutoX I looked it up and it states "Catalyst System Efficiency Below threshold (Bank1)" I can also use the diagnostic section on my Garmin EcoHD it states something along the lines of "car is ready for emission testing", then shows me the code, and give option to clear, which when I do it stays clear for several days Little data Car has 75K Borla Catback Exhaust installed at approx 50K WMW Downpipe Installed shortly before catback Never had a CEL since install My *guess* is maybe one of the 02 sensors Ideas?
Yep, I get em all the time. O2 sensor probably on its way out. Probably happens after a hard acceleration and quick lift, at least thats how mine does it. A few days of driving around like a sane person clears it for me or I can clear it at will.
I thought the 420 code was used strictly for the rear O2 to monitor the catalytic converter? I was always under the impression that if the pre cat O2 went bad, an A/F ratio system too lean/rich code (can't remember the numbers) would pop up if that sensor was going bad. Am I mistaken? I have a RMW street header and have been getting the P0420 code since the install and always thought it was because of the problems with the catalytic converters used during fabrication. I bought an O2 simulator to install in hopes of clearing the light so I can get my car inspected (its only overdue by a year!!) Steve
I would really like to know too. What is the group experience in resolving this code? I currently have that code and an inspection coming up, those 02 sensors aren't cheap.
No, I'm using an early 1st generation OBX header that has been on my MINI for years. I would just like to know what others have found to be the cause of the not so rare P0420 code.
A not so good seal at the header/cat-back joint can throw it. Only gasket i have found to be worth poop is the oem one. Had the code, replaced that gasket, and code no more. Sent from my DROID BIONIC using Tapatalk
I have a RMW Header and Milltek Cat back and had the same code a while ago. It was NOT the header but a crap gasket I used that caused the 0420. while I was troubleshooting, I switched the O2 since they are the same front and back, cleared the codes and reset the adaptives and the code still came back. I ended up replaceing the crap gasket (Vibrant 2-Bolt High Temperature) with a Remflex graphite exhaust gasket and this worked for me. Remflex Exhaust Header / Manifold Gaskets
Good info so far, searched the net for PO420, all makes and models throw this code. I'll bet across the board a few million has been spent by people trying to resolve this code. Maybe the EPA/DOT allowed this code as a bone for the Stealer/Dealers to corner and gouge us devotees to the internal combustion engine.
Yep that's why my mounted Scangauge comes in very handy :cornut: And for my also works for my P0128 thermostat code in the summer
I'm using a bit of software called Dyno-Scan by Auterra that I bought years ago for my blackberry. Only reason I still keep that old phone.
I used two anti fouling spark plug bungs to keep the rear O2 sensor honest, works like a champ. Going to get the stainless steel bung now that I know this works. Just Google it, "universal 02 simulator cel fix"