My R/T has thrown p0420 twice now. I noticed that it comes on after the vehicle idles a lot (its January in nw Indiana, on breaks at work it gets a little chilly) I could be wrong. But that's how it seems to work out. I just replaced a lot of stuff including plugs, pvc valve, cleaned throttle body, installed home brew Cai, and a new oil breather and the hoses from the oil breather and pvc they were cracked. local autozone had Lucas fuel cleaner on sale picked up a few bottles and ran em through full tanks too. My question is what's next? I'm gonna pull the o2 sensors tomorrow. Could maybe just cleaning em up with some carb cleaner work? Or just replace both and go from there? Also through code p0645 but that's for the A/C. Any help is always appreciated

 

And I should add that I couldn't see much oil in the intake when I cleaned the throttle body but I didn't have a good flashlight. I'm at 208,050 miles roughly also. When I changed the number 8 plug it smelled funny. Can't really pinpoint the smell is though. The plug didn't look any different from any of the others. And the plugs didn't look lie they had any excess burn marks, just looked like old plugs

 

Did a search and I keep seeing change the o2 sensors. Does anyone have the Denso part numbers? I found 2 upstream and 2 downstream part numbers. I only need 1 of each so what did yall use??

 

I would say your cat is bad

 

But it runs too good, I don't hear any rattling inside the cat when I shake it, and the exhaust doesn't smell. And I'm really not getting bad fuel milage.

 

a bad cat will throw a Catalytic Converter Running Below Threshold code. If he has these codes after erasing and NOT changing the O2 sensors. i would say replace the O2 sensors.

 

I would say the same do what you think is cheapest first. Could just be one sensor. Try the pre cat O2 first and go from there.

 

a catylitic converter efficiency code (P0420) is one of TWO THINGS

1) POST CAT (after the cat) O2 sensor,
2) bad CAT

dont waste money chaning the pre-cat sensor it is not the problem.

 

Do you have any other codes when reading it with a scan tool? and hmmm never knew that the pre cat wouldnt cause a 0420 guess you do learn something new everyday

 

And yes i saw the 0645 but im just wondering if you used a scan tool or just did the key trick to get the codes.