In the search for lower fuel consumption, engines have become leaner, have higher compression ratios and combust at higher temperatures. This results in relatively low CO and HC emissions, but high emissions of NOx. In order to counter this effect, after-treatment systems have been deployed, but cold starts remain a problem. The high NOx emissions can be reduced in several ways. Full vehicle testing is essential for obtaining the best results. OWI-Lab has the proper testing equipment that is also suitable for large off-highway vehicles.