So everybody (98.3% of people who have headers) knows the dreaded P0420 code!
There have been numerous solutions this problem presented in the previous decade.
Numero Uno: getting an o2 bung welded after the cat (* Definitely the most legit method (highly recommended if you want to get rid of the code and actually have a reading from your o2 sensor that will still be more or less consistent w/ ur stock setup ---> Possibly better for your fuel/air ratio if you do not have a piggy back, but I don't have a proof nor knowledge in the field.)) (Should run you bout $20 at an exhaust shop)
2nd: o2 bung extender, I have heard that this works, but was unsuccessful in my attempt because the extender didn't fit correctly and would cause the o2 sensor to sit dangerously close to the front sway bar. (Should run no more than 7 bux)
3rd: o2 Sensor simulators. There have been known to successfully get rid of the problem, at least the legit ones, but the universal one I got from o2simulators.com that was suppose to work according to a few other members got rid of my p0420 code only to cause the ecu to throw a P0138 (voltage to high blabla) And these are the only simulators I'm aware of that are still available new... will run you anywhere from $40-$50
Now I recently stumbled upon a solution used on a maxima way back whenever... there is a detailed explanation of how this works on the thread I got the idea from(will be posted at the bottom for reference), and I'm guessing it functions essentially like the o2 simulator but for a ridiculous fraction of the cost and so easy a 3rd grader can do it....!!!!
Step 1. Acquire resistor
You need one 1.2K 1/2 watt resistor - you should be able to get them at your local electronics store or if you google them you will find countless options of where to get em...
Step 2. Locate the o2 sensor signal wire
Look at the wiring of the o2 sensor in the FSM for your year to make sure that the wire colors correspond, but typically the black wire on your o2 sensor will be the signal wire, this is the one you want!
Step 3. Cut the sensor wire and solder/crimp the resistor in to the signal wire.
Step 4. Tape it all up probably don't want to put tape over the resistor as it will get hot, but I did, and its been fine so far...dont ask why....
Step 5. Clear the code, or disconnect the battery overnight, and pat yourself on the back because you got rid of that damn code for less than a buck.
The code has been gone for weeks now and I doubt it's coming back but I will keep you posted if it does return. Although for less than a buck this really can't hurt to do if that's the only code keeping your service engine soon light on.
Sorry no pics, but it's very easy and should only take 15 minutes.
Props to Danny 7633 for figuring this out.