How are vehicle's emissions tested?
The Gateway Vehicle Inspection Program uses On-Board Diagnostics or OBDII for the emissions test. This testing uses a computer system installed in all 1996 and newer gas-powered and 1997 and newer diesel-powered vehicles 8,500 pounds or less in Gross Vehicle Weight Rating. OBDII is a system that monitors the vehicle’s emissions-control devices and other engine-related parts to make sure they work.

During an emissions test an inspector will attach a connector cable to the OBD port on the driver’s side of the vehicle. The inspector's computer connects to the vehicle's computer to determine if the car is working properly. To pass the test all emissions parts must be working. If any issues are found, the vehicle will fail the test for reasons printed on the vehicle inspection report. Finding these emissions problems early allows motorists to invest in needed repairs to make sure their vehicles continue to work properly.

For more information see On–Board Diagnostics (OBDII) Fact Sheet.