Check Engine Light Code P0420

Got the CEL light yesterday in a 2001 DC 4x4 auto, ran by autozone, diagnosed as P0420, catalytic converter. Checked for leaks in exhaust below manifold and in between the catalytic converters, nothing. Noticed a strange sound coming from the second catalytic converter, not pinging, but just louder than the other one. Also, I noticed a slight decrease in performance of the truck. Could it be a restricted catalytic converter? Cost? anybody had this issue?

I have a buddy who can get O2 sensors for cheap, so I am going to try to replace the O2 sensors in hope that this is the problem.

 

found another thread with the same issues and same code

got these error messages

1. Air leak in exhaust before rear H025
{Heated Oxygen Snsor bank 1

2. AF sensor error

3.Fuel system fault

4.Faulty Catalytic converter

Is it most likely the cat?

 

I just got done fixing this same problem! First off check for exhaust leaks. If none, then see If your cats are still good, tap on them and see if it rattles, this may indicate its bad. From the sound of it, its posibly your cat.

But the most commin problem is your AFR sensor or o2 sensor has gone bad. That was my problem. And Its reccomended to change them both at the same time. How many mile's are on your truck?

Sorry. Not sure on cost of a new Cat.

 

What are the part numbers for the O2 sensors (upstream is the A/F sensor)? I hear Denso is the way to go, correct?