The terms smog check, smog test, and emission check all refer to the same thing. There are two different ways a smog check is implemented: ASM & TSI. TSI (Two Speed Idle) test is used to inspect all wheel drive (AWD) vehicles. The vehicle is inspected at 2500rpm and idle. This is how all vehicles were inspected prior to 1997. ASM (Acceleration Simulation Mode) test procedures involve operating the vehicle on a dynamometer at 15 mph and 25 mph under load. Operating an ASM test allows for the measurement of a third pollutant nitrogen oxide (NOx).