Registration > Inspections & Emissions > On-Board Diagnostics

On-Board Diagnostics (OBD) is a computer-based system built into all 1996 and newer light-duty passenger vehicles to monitor the performance of some of the engine's major components, including emission control components. The OBD system helps the motorist know if their vehicle has a defect that could cause excess pollution. In addition, it helps mechanics accurately diagnose problems and make effective repairs.

Vehicle Requirements

1996 and newer model year light-duty gasoline-fueled passenger vehicles (8500 GVWR and less) and 1997 and newer model year light-duty diesel passenger vehicles (8500 GVWR and less) must have an OBD test as part of the inspection process.

1996 and newer vehicles subject to the OBD inspection are required to pass the test and will need to have repairs done if the vehicle is "Rejected." Only one, sixty (60) day repair period is allowed per inspection cycle for vehicles rejected for OBD failures. Address OBD rejections early so that there is sufficient time to complete the needed repairs.

Check Engine Light

The Check Engine Light, also known as the Malfunction Indicator Light (MIL), is a warning for vehicle owners that a problem has been detected in the emission control system. If the light comes on and stays on, the OBD system has detected a problem. This could be as minor as a loose gas cap or as major as an emission component failure. Your vehicle will be rejected if the light is on when it is tested.

Passing the OBD Inspection

Ongoing vehicle maintenance is the best way to keep your vehicle running properly and ready for inspection. Many of the emission control components can be checked and repaired during routine service. Follow the manufacturer's recommended maintenance to help your vehicle run at its best. This will also help get better gas mileage.

OBD Rejections

A rejection indicates that a problem exists that could compromise the efficiency and smooth operation of your vehicle. Rejected vehicles must be repaired and pass the inspection before an inspection sticker will be issued. A one time, 60-day repair period will be allowed to have necessary diagnostics and repairs performed, and to have the vehicle re-tested to verify repairs.

If your vehicle passes the safety inspection but fails the OBD inspection and you cannot afford the repairs to the emissions, you may be eligible for an Economic Hardship Waiver to allow more time to save the money to complete the repairs. For an application call the DMV OBD Program at 271-0352.

Reasons for OBD Rejections

Your mechanic will provide more information and discuss why your vehicle was rejected. Rejections can be due to several reasons, including:

• Not Ready - The system in your vehicle is not ready to be tested. This could be due to recent repairs or if the battery was recently disconnected. In most cases, a week or so of normal driving should make your system ready. If it takes more than a week, you should have the vehicle checked, as there may be another problem.
• Non-Communication - Your vehicle will not communicate with the test system. Make sure the Data Link Connector (DLC) is accessible or has not been damaged.
• Check Engine Light is On - The most common failure. The Vehicle Inspection Report will print Diagnostic Trouble Codes (DTCs) related to the specific problem to help a qualified mechanic diagnose the problem and needed repair.

For more information please visit the links below:

• New Hampshire OBD & Safe Testing Program
• US Environmental Protection Agency

Contact Information

• State of NH OBD Program: (603) 271-8800
• Economic Hardship Waiver: (603) 271-0352