P0420 - O2 sensor failing or Cat died?
 

Hi,

Getting code after Diablotune 91 octane. It comes every 80-20 miles. Clearing it with tool and back again. Looking graphs with obd torque. Sensor 1 is fluctuationg. I dont know where to start. Replace 02 sensors or gut the cats. I visually check cat convertors was fine. 76K on odometr :twitch:

I would revert back to stock tune and see if this returns.
P0420 is for bank 1 which looks good. There was fluctuations in bank 2 cat monitor sensor.
If anything I would think u would see P0430. The long term fuel strategy even though in spec is a tad high. Adding fuel. U like to see FT near 0 short and long

P0420 is fine, and the sensor is still being monitored, even with the code set. I
had a P0430 set Wed., but after 200+ miles, it went out on it's own. I had just
changed the VVT Solenoids prior. When I changed the throttle pedal, I got a P0420,
that went away. These cars are very sensitive to changes. Every time I make a
change on the engine, I get one of those codes. Once it's cleared, or goes away,
it does not come back till I do something else.

P0420:
That means your passenger side DOWNSTREAM sensor is detecting too much flow,
or too much oxygen in the exhaust. Since there are no upstream flags, the A:F
ratio it still within parameters. I ran with P0430/20 codes for months, no issues.

When the downstream sensors start reading the same as, or higher than, the
upstream sensor on the same bank, that is when the CEL is set. It's not a clog, rich,
or lean condition. Rich and Lean will be set by the upstream sensors if detected.

All you will need to do if persistent, is add spacers to the DOWNSTREAM sensors.
That's all I did. I do not have secondary cats either, and I have hi-flow primary cats.

THOSE are the codes you would get if you removed the cats, or put long-tube
headers on. Anything that increases exhaust flow, will set those codes.

HOWEVER, you do not need to worry about anything, the car will run and perform
just fine.

I think just order spacers for downstream sensors. I don't need new sensors yes? Just spacers and it all?