Massachusetts uses the car's own diagnostics. The annual inspections plugs in to the OBD port and looks at the emissions system codes. They check more on 2002 and newer cars.
Used to have the tail pipe wand checking the gasses coming out. Later combined that with a dynamometer where they would strap down car and run it up to 50 mph. Got rid of those in 2008.
Used to have the tail pipe wand checking the gasses coming out. Later combined that with a dynamometer where they would strap down car and run it up to 50 mph. Got rid of those in 2008.