Cat Codes and Tough O2 Sensor

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WarrenBoostit

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Recently, I reduced my E content I was using on my GH AO 93 tune to cover for bad winter gas, down to 15-19, and I received a CEL for 0420 and 0430, cat efficiency below threshold. Seeing as it was both banks simultaneously, and right when it's warming up and lowering ethanol levels, and I'm at 61k miles, with catted downpipes, I have to assume it's not the cats going bad (though my fuel trims did go up on Ethanol, crossing my fingers that wasn't rich enough to hurt them).

The first thing I am trying is the precat o2s. I figure at 60k they're probably going bad anyway, so I got it up on my rhino ramp, the first O2 was a breeze, but the firewall side O2 is an actual PIA nightmare that I wasn't able to remove. I'm guessing I need to remove the wheel on the passenger side next, but does anyone have any other tips to get at this better? I tried O2 sockets, adjustable wrenches, bending ratchets, nothing could get the leverage or space I needed.

Having one installed didn't stop the codes from coming up, and I almost expect the other one to not fix it as well. Any idea why a car at this mileage would be getting this code? One thing I saw that might make me concerned is that there is a darker coating on the flex pipe of the downpipe coming from bank 1 (firewall side, exhaust to the right side of car). Not sure what this is or if it's related.

The only performance issues I've noticed is rough idles on cold starts, the needle dances for a bit. Otherwise, if the car isn't performing, it would be hard to tell, since it still flies.



Black 2018 SHO Non-PP | GH e30/AO Tune | PPE Catted Downpipes | DG2 Trans Mount | M-12405-35T plugs at .026 | 170 Tstat | 3 bar | H&R Springs | XDI-35 | Badges removed | Chrome delete | Fuel-it Bluetooth ethanol analyzer | GH IC | EPP Gen2 CAI | Noisemaker delete | MSD coils | Ceramic coating | Window Tint | EPP Hot Pipes | Black AR924 w/ General GMAX AS 05 255/45r20 | MRT axle back w/black tips
 

Ta2dResqr

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Cat efficiency codes are usually rear. The fronts tell how rich/lean the motor is and the rears tell how well the cats are cleaning up what the sngine puts out.
 

WarrenBoostit

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Cat efficiency codes are usually rear. The fronts tell how rich/lean the motor is and the rears tell how well the cats are cleaning up what the sngine puts out.
Weird, I've seen a lot of ecoboost forums online argue about this and say the opposite, I've heard the rears are expected to last much longer. There's 4 total right, 2 per exhaust? Would both of my rears have to go out to get an 0420 and 0430 simultaneously?
 

Ta2dResqr

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Not saying that is the reason for a simultaneous code. Merely stating a rich or lean code that had no other cause would be a pre-cat sensor and a cat efficiency code with no other cause would be post-cat sensors. How are sensors upstream of the cat going to know how well the cat is working? You stated you are replacing the pre-cat sensors. I am saying that I do not see that as being your issue. If you had a large STFT and LTFT indicating a rich or lean condition in addition to what you have told us, then I would look at them. With only 2 post-cat related codes, struggling with and replacing the pre-cat is pointless.
 

Ta2dResqr

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DTC P0420



Symptom Descriptor Catalyst System Efficiency Below Threshold (Bank 1)



Verified Fixes

Fix Description
Spark Plug
Ignition Coil
Catalytic Converter



Probable Causes
Catalytic Converter
Cylinder Misfiring
Downstream Heated Oxygen Sensor (HO2S)
Wires Connected Incorrectly
Evaporative Emission (EVAP) System Purge Valve Stuck Open
Exhaust Leaks
Exhaust Manifold
Exhaust Pipe
Fuel Injector Leaking
Muffler and Tailpipe Assembly
Oil Contaminated
 
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