A defective EGR valve can cause high NOx. We recommend inspecting the EGR
valve first before suspecting the CAT; or Catalytic Converter. The EGR valve
re-circulates exhaust gas back into the combustion chamber. This cools down
the chamber temperature keeping it below 2500 F; NOx is created when engine
temperature reaches over 2500F.
Since you mention all other emissions numbers look good, specifically CO, we
would recommend inspecting the EGR system first, and then the CAT on your
Chrysler.
