P0420

[RedMechHVAC]

Hello. First time post here. My name is Robert. I'm an HVAC tech in Tucson, AZ and joined this forum primarily to learn from some of you guys to get better about working on my own cars.


I have a 2013 Nissan Pathfinder that recently hit me with a P0420 code after changing my oil. I normally use synthetic, but this time went with Royal Purple and put a few ounces of MMO in the gas tank for good measure.


I can't help but wonder if the two events are related, but I may be wrong.



In any case, I hooked up my scanner and looked at some of the live data once the car was up to running temp. Both banks of O2 sensors are behaving pretty similarly, although I'm not sure which sensor designation is upstream or downstream. Sensor 2 is toggling between .2V and .8V. Sensor 1 is holding at about 2.2V. I got under the car to measure some temps. Both precats are about 280*F going in, and about 300*F going out. At the post cat, I'm getting about 295*F going in, and about 200*F going out to the mufflers.


At this point, the best I can tell is that the post cat is to blame, but I'd like to be sure before I go spending time and money trying to fix it.


Also, the exhaust smells terrible.


Thanks in advance for any help.

[Stealthee]

Terrible smelling exhaust and P0420 would indicate an issue with the main cat.

[RedMechHVAC]

Thanks for the reply.

If that were the case, which main cat would it be? Both seem to be doing the exact same thing in terms of their temperature differential and what the O2 sensors are doing for each bank.

What should the temperature differential be on the post cat?