P0420 code/O2 sensor replacement

Hey does anybody have advice on what the P0420 code could possibly mean beside the cat going bad? I have an ultraguage and it's showing that pending code. If it is the o2 sensors, does anybody have any write ups?? Thanks! 02 xtra cab taco!

 

I had that on my 95.5 (pretty much everyone gets it eventually). Usually the pre-cat O2 sensor. In either case it is super simple to change both O2 sensors, just two bolts (be careful not to shear the studs off, I sheared one off). Not sure if you have the V6 (5VZ-FE) or the 4cyl (3RZ-FE). This screenshot is for the 5VZ-FE since it is more common, the 3RZ-FE is similar to the non California Spec 4WD illustration though.

 

Might be worth a shot to make sure your PCV valve functions properly (also extremely easy to replace and check).

This illustration is also for the 5VZ-FE (The 3RZ-FE is even easier to get to the PCV valve on, easy to find info on too)

 

Most of the time its what Speedy here said. I had a p1135 which is the direct code for the pre-cat o2 sensor. But, I have spoken with multiple mechanics and people that have fixed this code and most of the time its a bad o2 sensor. But start with the PCV valve first. Cheap and simple to replace.