The car(2000 max, auto) is throwing that code and its having a really bad problem with just shutting down....it can be in park or sitting at light with foot on brake. Any help?

Thanks

 

Do you have a rough idle before it dies, like maybe the engine is not firing on all cylinders? If so, I would guess that's triggering your p0420 because of unburnt fuel hitting the o2 sensors.

You might want to have your ignition coils checked if you haven't already. There's defect in original coils that many people had to deal with. Engines with that problem usually have a p1320 error code, but not always.

http://maxima.theowensfamily.com/tsb/NTB01-059.pdf