In 2010, the EPA imposed strict regulations on diesel vehicles to ensure emissions guidelines were followed. All diesel vehicles were required to use diesel exhaust fluid (DEF), and if drivers ignored keeping their DEF tanks full and using good quality fluid, the vehicle would experience what is called derating. The problems stemmed from faulty DEF sensor readings, which caused engine computers to “derate” or severely reduce operating speeds. This left operators of heavy-duty trucks, motor homes, and buses on the side of the road, requiring a tow to the nearest repair shop, and kept them stranded for days waiting for parts.
There is light at the end of the tunnel. In 2027, the EPA will change the rules that apply to derating and heavy-duty vehicles. Instead of going from 65 mph to 15 mph, the reduction will reduce to 60 mph for several hours, and if warnings are not adhered to, it will slowly reduce from there until DEF is added, or repair is completed. It is up to the manufacturer to decide if they want to take on the expense of reprogramming vehicles prior to 2027. Happy Motoring.