Failed smog, to high ppm NO

[hidesertwheelin]

The max allowable reading is 963 PPM, I measured 1172 PPM at 15 mph. Any ideas? Oil change and tune up? I have a small exhaust leak before the cat ( newer cat), would that do it? Everything else passed.

 

[mosesburb]

Malfunctioning EGR valve or a bad cat would be my first thoughts. High NOx are a result of high combustion temps. The EGR valve's primary function is to reduce combustion temp. The cat should have a NOx bed in it (provided the replacement cat was a 3-way unit and not a cheap 2-way--I don't know of a way to visually distinguish between the two though). Typically oil changes and tune ups are more aligned with HC or CO failures, but if its been so long that you think they may be necessary, it wouldn't hurt--just probably won't help your situation any.