The DMV is a great source for information regarding vehicle inspections performed in New Hampshire. For specific questions regarding station regulations and inpsection laws, please call the Inspection Desk or visit them online.
Inspection Desk: 1-603-227-4120
Online: NH DMV Website
DMV Introduction to OBD Emssions (taken from the DMV websiste)
Emissions Program Passenger Cars & Light Duty Trucks
In 2005, the state of New Hampshire implemented statewide OBD II emissions testing. This means that vehicles will need to pass the OBDII emissions test in order to pass the annual safety inspection.
The OBD II test is part of the annual vehicle safety inspection. When your mechanic finishes the safety inspection on your vehicle, he/she will enter the results of your inspection into a computer (NHOST unit) that gathers and stores test result data. If your vehicle is a 1997 or newer car or light duty truck (8,500 lbs. GVWR or less), the computer will prompt the mechanic to perform an OBD II test. To perform the OBD II test, the mechanic will attach a cable to the data link connector (DLC) in your car. This will enable your car's computer to communicate with the test equipment. The computer in your car will then relay data about your vehicle's emission components to the NHOST unit. At the conclusion of the test, the NHOST computer will print a Vehicle Inspection Report (VIR) that will provide you with detailed information about your inspection results. The mechanic will sign the VIR and give it to you along with any other informational pages that print.
OBD II emissions testing is part of the Environmental Protection Agency (EPA) Clean Air Act Amendments of 1990. All cars and light duty trucks manufactured in 1996 or later are required to have second generation on board diagnostics (OBD II) computers to monitor engine conditions and components. The OBDII computer helps to assure that the engine is running at peak efficiency and also alerts you to any malfunctioning emissions control components that require attention. When the OBDII system detects a problem with the emission control system, a "check engine" or "service engine soon" light (also called a Malfunction Indicator Light or MIL) is illuminated on the dashboard. If your vehicle's MIL is illuminated, it will not pass inspection and you will not be issued a windshield inspection sticker until proper repairs have been completed.
By continuously monitoring the well being of your vehicle's components, the OBD system can identify minor problems that can be repaired easily before they become more serious and expensive to correct. Not only can you save money on repairs, but you will also get better gas mileage, which will save you money at the pumps!
OBDII systems are very complex, so it is important to have qualified technicians make the repairs to your vehicle. When shopping for emissions-related repair service, be sure to ask if the mechanics performing emissions repairs to your vehicle are ASE A-8 or L-1 certified.
Thank you for doing your part to keep your vehicle safe and the air clean.