On October 1, 2007, the State of New Hampshire transitioned into the final stage of the OBD emission program. All automobiles and light-duty trucks whose model year is 20 years old and newer must now pass an OBD emission system inspection during its inspection period. This helps ensure that the vehicles on the roads in New Hampshire will be running cleanly and efficiently in accordance with the US Environmental Protection Agency regulations and keeping our environment and air quality healthier for us all.

Windshield Sticker

The windshield stickering process that was implemented in February 2018 now applies to all 20 years old and newer vehicles that require an OBD inspection. Depending on the result of the safety and OBD inspections, a vehicle will receive a sticker that expires in the owner's birth month, or a sticker that expires in 60 days, or no sticker as shown in the above table.

How the OBD System is Tested

The OBD system test consists of several individual checks. Failing any one of the tests will result in an overall failure of that vehicle for the emission portion of the NHOST inspection.

1. MIL Check During Key On, Engine Off Operation

   This is checked manually by the mechanic. The Malfunction Indicator Light, or MIL, should illuminate when the ignition is in the Key On, Engine Off (KOEO) position, often labeled as the Run position. If your MIL light fails to light it could indicate that the OBD system is not functioning, that the MIL bulb is not working, or that the system wiring is damaged.

2. Diagnostic Link Connector Check

   This check is also performed by the mechanic. The Diagnostic Link Connector (DLC) is the port into which the NHOST inspection unit connects when performing the OBD test. The port, which is standardized and required on all 1996 and newer passenger vehicles that have a gross vehicle weight rating (GVWR) of 8500 lbs or less, is usually located under the dashboard on the driver's side. If the DLC port has been cut out, stuffed behind something so it is inaccessible or has otherwise been damaged so that the inspection equipment cannot connect to it, the vehicle will fail the OBD test.

3. Communication with Vehicle

   The NHOST inspection unit automatically performs this check, which simply ensures that the inspection equipment is able to read the OBD system monitors. If it is unable to properly communicate with the vehicle, there is a problem with the OBD connection or system that needs to be addressed.

4. Vehicle Readiness Check

   This check tests to see if the vehicle has gone through the proper drive cycle(s) to be ready for testing. A drive cycle is a particular series of events that need to occur for the monitors to properly evaluate how the vehicle is performing. For example, part of a drive cycle might be driving at 40 mph for 5 minutes, idling for 15 seconds and driving in stop and go traffic for 15 minutes. Check your owner's manual. Each manufacturer has their own drive cycle and vehicle makes produced by the same manufacturer may even have some variation. Most people will complete the drive cycle for their vehicle in no more than three days just by using their normal driving routine. Vehicles that are only driven for short distances or at low speeds may take longer to complete their drive cycle and/or require special operation such as at higher speeds.

   Issues with completed drive cycles prior to the NHOST inspection are typically only of concern when the OBD system has been "cleared" to remove previously recorded DTCs. This would be done when a previous problem was corrected and the mechanic cleared the OBD system after making the needed repairs so that the check engine light would no longer illuminate. Unless you have had recent work done that required this clearing, your monitors should all be ready. If there are monitors that are not ready, however, the vehicle will not pass the OBD test.

   Click here for an additional note on Diesel Monitors.

5. MIL Commanded On

   This is an electronic check that has two purposes. First it is a deterrent against someone improperly tampering with the OBD system in an attempt to obtain a passing test when the vehicle has OBD defects. Second, if the MIL is commanded on and DTCs are present, it indicates a serious problem with the vehicle. If the MIL is commanded on for any reason, the vehicle will fail the OBD test.

6. MIL Light On While Engine Running

   This test is a visual check performed by the mechanic if the NHOST inspection unit is unable to communicate with the vehicle as described above. It is used as a catch-all check in case the other above checks cannot be performed. If the MIL light is on while the engine is running, the vehicle will fail this check.

Vehicle Inspection Report

At the end of an emission test, the OBD inspection machine will print out a Vehicle Inspection Report, or VIR. The station should present this VIR to you as it is designed to let the motorist see the results of the inspection including whether or not the vehicle was passed or rejected. If it was rejected, it will list the reasons why it was rejected. We recommend you keep the VIR in your vehicle as added proof that you have recieved a proper vehicle inspection. Click here for more VIR Details.

What if your Vehicle is Rejected

If your vehicle was rejected, you will need to have proper repairs made. A diagnostic evaluation is the first step. Be sure that your vehicle is diagnosed and repaired by a qualified OBD trained technician. Generally, people who are qualified to diagnose and repair OBD are ASE L-1 certified. Your vehicle may be eligible for warranty repair under your vehicle emissions warranty or the federal 8/80 warranty. Also, check for recall notices or technical service bulletins prior to authorizing repairs. Consult your vehicle owner's manual or dealer.

If you believe that your vehicle should not have been rejected for the OBD inspection, you may request a Referee Action within 10 days of the failed OBD inspection. Do not have any repairs made to your vehicle prior to contacting the NHOST Helpline. Your inspection results will be evaluated to determine if your vehicle qualifies for Referee Action.

Of all the vehicles on the road today, the vast majority will pass an OBD emission test. If you properly maintain your vehicle on an ongoing basis your vehicle will most likely pass smoothly through that portion of the inspection. But, if you are one of the few whose vehicle has an OBD issue, here is some information about what that means for your annual inspection.

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 the vehicle re-tested to verify repairs.