We recommend checking your Buick Electra's fuel control system first to make sure your engine is not running "lean". A lean fuel condition means enough fuel is not being delivered to the combustion chambers, causing the engine to run hot. NO is created when engine combustion temperatures rise above 2500f.
If fuel control is optimal (as close to 14.7:1 as possible) check engine compression. If compression is high (check your vehicle's repair manual for proper compression requirements - they should be on average around 110 PSI) you'll need to decarbonize the engine to lower compression and get your Buick's engine running cooler.
You should also make sure your Buick Electra's EGR system is functioning correctly. The EGR system is also responsible for lowering NOx emissions.
For more high NO faults click here.