Bob is correct, here in Alberta, when a commercial truck is pulled over if anything is not per the known spec you are impounded, NOW, no questions asked. While the emissions equipment is not required here in Alberta it is still part of the known spec for the vehicle. The Commercial Cops are charged with the total aspect of safety of commercial vehicles and any and all maintenance and or modifications must be of an approved nature. So the general rule is if it looks right it will be a warning and not a citation. The major concern is weight, brakes, registration, and any safety violations. Attitude of the driver can play a huge part of acceptable compliance if nothing visible or obvious is found. This explains why many hot shot operators run unmarked vehicles. However if you pull a trailer of any type you had better be prepared to be pulled over, personal use or commercial, THEY are looking for infractions, weight , hauling limits, certificates of compliance ETC. Life can be such fun! LOL