Any input here would be much appreciated. The check engine light came on on my 2005 TL. Put the scanner on there and got the P0420 code (bank 1 catalyst below threshold). So I did some live scanning of the o2 sensors, and both front and rear were performing properly, which also showed that my catalytic converter was doing what it's supposed to as well.

If im getting the P0420 code and it's neither the o2 sensors or the catalytic converter throwing the code, does anyone have any other ideas as to what it could be? Or has anyone else experienced something similar to this?

Any information you guys have will be a huge help to me. Thank you in advance

 

had this issue last month, turned out it was bad gas (i refilled while tanker was at station).

ran the tank to 1/4 empty and bought some royal purple octane booster to throw into my tank with my next fillup at a trusted BP station.

did not need to clear codes or anything it went away by itself

you use premium right?

https://acurazine.com/forums/3g-tl-p...sensor-938841/

 

i bet its the cat. how can you tell from a live stream of o2 sensor activity that the cat is "doing its job"? a very small change in efficiency is all it takes to throw the code on

 

yes, I always use premium and fill up at the same station almost every time. Maybe I'll try and use some royal purple or sea foam in the next tank and see if that helps at all

 

the values I got for voltage on the o2 sensors were:

2.1 down to 0.1 for the first sensor
0.5 steady for the second sensor.

are these readings out of the ordinary?

 

Rather than a write up, although for GM, here's a way to check:
Part 3 -How to Test Trouble Code P0420 (GM 3.8L)

 

Bad cat cuuuh.

 

Bad cat. Or lazy sensor. The code is thrown when driving at a constant speed on the highway so no way for you to be monitoring at that time. Even if you did, I still say it's the cats.

 

I mean... i wouldn't say "NO way".. there are live data OBD2 scanners..

 

Blow some weed smoke into the intake.