NOx emissions are normally due to defective EGR valves and/or systems. High compression, high engine temperatures, and/or vacuum leaks may cause high NOx also. If after all emissions systems are inspected and no faults found, consideration should be given to your Dodge Dakota having a defective Catalytic Converter.
The most important two systems which you should inspect for faults are the EGR system and fuel control system. If your Dakota is running lean, high NO will be created. A lean fuel mixture is when the engine receives less fuel then is necessary to obtain efficient combustion. Lean fuel mixtures are often due to vacuum leaks. These leaks will allow the suction of additional and un-metered air into the combustion mixture or exhaust (depending on where the vacuum leak is located) disturbing pre/post fuel combustion and increasing NOx emissions.
