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New Hampshire Department of Environmental Services

On-Board Diagnostics (OBD) Systems

Automobiles manufactured since the early 1980s are equipped with systems help repair technicians identify problems associated with the computerized engine components. Known as on-board diagnostics, or OBD, systems, they are made up of sensors that communicate data to the vehicle’s computer. Since 1996, more advanced OBD systems, referred to as OBD II, have been required in all passenger cars and trucks as a result of the federal Clean Air Act Amendments of 1990. These systems monitor the vehicle’s exhaust and pollution control devices to ensure that they are operating properly.

How the OBD System Works
OBD systems provide owners with an early warning of vehicle malfunctions that can increase emissions, often before the driver is aware of them. When the OBD system detects a problem, a dashboard "Check Engine" or "Service Engine Soon" light (also known as a Malfunction Indicator Light or MIL) is illuminated. A corresponding diagnostic trouble code is sent to the computer's memory indicating which emission control component is experiencing the problem, and under what driving conditions. When the vehicle is taken in for service, a repair technician retrieves the code information using a scan tool which allows him or her to accurately diagnose the problem.
OBD systems not only protect the environment, they also help consumers by identifying minor problems before they become major repair bills. For example, by detecting a relatively inexpensive repair like the replacement of a bad oxygen sensor, an owner can save the cost of replacing the catalytic converter later. OBD can also help save fuel and money by making sure gasoline isn't wasted as a result of a loose gas cap or incomplete combustion.

New Hampshire Vehicle Safety Inspection Testing Requirements
Since 2005, New Hampshire's annual vehicle safety inspection has included a scan of the OBD system on all 1996 and newer passenger cars and light duty trucks. This statewide system enables inspection stations to perform OBD testing in conjunction with vehicle safety inspections and electronically collect and report the results to the NH Division of Motor Vehicles. The fully automated system (called the New Hampshire OBD and Safety Testing Program) helps ensure that all vehicle inspections are performed properly and fairly, reducing paperwork for the inspection stations.

An OBD system scans add less than five minutes to the inspection time. If a vehicle fails this portion of the inspection, the owner will be issued a report that documents the reason for the failure. The owner then has 60 days to have the vehicle repaired and retested. Vehicles may be inspected and OBD tested at any state licensed inspection station [] or authorized New Hampshire automobile dealer.   

Benefits of OBD
Modern cars emit less air pollution due to improvements in engine management technology and emission control devices. However, they are only cleaner when the equipment is working correctly. A properly operating OBD system monitors the engine, power train, emissions systems, and other components that can affect emissions, and ensures that the engine is running at peak efficiency.

For more information about New Hampshire’s OBD inspection program, see the following references or call NHDES’s Air Resources Division at (603) 271-6453.

Contact Us

  • Timothy White
    Supervisor, Mobile Sources Section
    New Hampshire Department of Environmental Services
    29 Hazen Drive, PO Box 95
    Concord, NH 03302-0095
    Tel: (603) 271-5552
    Fax: (603) 271-1381



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NH Department of Environmental Services | 29 Hazen Drive | PO Box 95 | Concord, NH 03302-0095
(603) 271-3503 | TDD Access: Relay NH 1-800-735-2964 | Hours: M-F, 8am-4pm

copyright 2017. State of New Hampshire