in a durango what typically causes this code? P0420 1/1 Catalytic Conv Eff
o2 sensor? cat? plugs/wires?

 

How along was your last tune up? Mine threw that code, I did a tune up cleaned the throttle body intake and ran some Lucas fuel cleaner and icleared the code and never came back. Change the o2 sensors, that could be the cause if not its the cat converter

 

did you change plugs, wires, distributor, etc?

 

o2 sensor POSSIBLY, but in my experience, I changed the o2 sensors, and the cat was bad/clogged.

 

post cat O2 sensor, or bad cat.

however if you clear the code and it stays away i wouldnt be too concerned about it. so try that and a tune up first.

 

is there a way to know which o2 sensor it could be? right or left? up stream or down stream?

 

Change both Downstreams if you aren't getting any codes

 

to my knowledge the 5.9 only came with 2 O2 sensors, one pre cat sensor and one post cat sensor, change the post cat sensor, (the one AFTER the cat, farthest away from the engine)