1997 T4R 3.4 4WD (non-cali) 237k mi

Recently I went on a 4 hour road trip down to Florida for a bachelor party. On the way there the CEL came on. I have one of those cheap chinese made scanners that I pair with the InfoCar and Car Scanner apps. I checked the codes. It came back as:

Confirmed
p0125 Insufficient coolant temperature for closed loop fuel control

Pending
p0130 Heated oxygen sensor (HO2S) 1, bank 1 -circuit malfunction

p0133 Heated oxygen sensor (HO2S) 1, bank 1 - slow response

I checked out the live data and the Oxygen sensor 1 bank 1 Voltage was 0 V and Oxygen sensor 1 Bank 1 Short term fuel trim was 0%. After some research, it appeared that my upstream o2 sensor crapped out. I came home and ordered a new upstream denso o2 sensor. Cleared the codes and everything appeared to be fine on the live data reading...

Days later I got the dreaded p0420.

Confirmed
p0420 Catalytic Converter System Bank 1 Efficiency Below Threshold

I figured I'd go ahead and replace my downstream o2 since I replaced the upstream sensor. Cleared the code and put in the new o2 sensor. Everything was working fine and I even gained MPG... a blessing in a lifted T4R on 33" tires. Everything is still working fine, but now I get the p0420 CEL code every few days. Anyone else have this experience? I'm gonna try to look for exhaust leaks.

Throttle body is clean. OEM MAF is maybe a year old. Spark plugs and wires are new.

pls don't be the cat pls don't be the cat pls don't be the cat

Im also chasing down a P0420. Tried fuel injector cleaners, spirited driving and replacing up and down stream o2's. Still P0420 comes up after doing the drive sequence.
Got a infrared temp gun to measure before and after cat temps.
The cat IS plugged up and needs to be replaced based off a lower temp after the cat. So, my next move is replacing the cat.

Chased the same code for 2 years, finally had a universal magnaflow cat installed. No issues since. Save yourself time and money and replace the cat.


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