Lt1 was down for 4/5 months, finally replaced the Opti and now its running again. Problem is, took it to get the emission test and it failed again. The problem being high NOX. NOX came in at 2.20, allowed is 2.0. I unplugged the coolant sensor due to it being faulty sometime ago to remove the notification of low coolant on the dash. Will this act alone, cause me to fail emissions?

 

If you have an aftermarket cat on there, see if you can put a stock one on for the test. Back when I was going though all that, the stock cat was way better on HC, CO, and NOX than the aftermarket one that was only a year old.

If you have a known good stock cat on there, then egr not working, engine temp to high, timing too advanced...

 

The low coolant sensor would have no effect. It is just a light on the dash. No computer interaction whatsoever.