It's important to also look at the CO emissions your Cadillac produced. If
CO was low then you might have a high NOx problem due to a lean fuel
condition. If CO is right on mark or above normal, your Cadillac's high NOx
fault may be due to the EGR valve. NOx is caused due to increased engine
combustion temperatures. Any engine problem which could cause the combustion
chamber temperatures to reach over 2500f will cause high NOx, i.e.. Lean
fuel/air mixtures, vacuum leaks, dirty injectors, bad fuel pump or dirty
fuel filter, defective EGR valve.
You see there are many things which could cause high NOx on your Cadillac.
We have to recommend a hands-on diagnosis by a smog check repair station.
There are too many emissions components which could cause this fault to
simply start replacing things, specially if the fault is as simple as a
vacuum leak which may not need replacement of any parts, just a 6"-12"
vacuum line... It's possible.
