Even when the Ammonia sensor was present again it detected ammonia , even very small amounts of Urea will create ammonia in the evaporation process of the water in SCR , their was no longer the Need for the sensor so it was removed... You can still meet the laws requirement ACA... 95% of the time with considerable less concentration. if you measure the NOx by volume , you would need to drive the vehicle over 1 million miles to create 7-10oz of NOx at 5% I'm just guessing at this because it would take years of Data to calculate exactly would it would be.