Basic Inspection Information — Mass Vehicle Check
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Mass Vehicle Check
Emissions: Vehicle engines and air pollution

The health risks of air pollution are extremely serious. Poor air quality increases respiratory ailments, such as asthma and bronchitis; heightens the risk of life-threatening conditions, such as cancer; and burdens our health care system with substantial medical costs. Particulate matter is singlehandedly responsible for up to 30,000 premature deaths nationwide each year.

Transportation is the largest contributor to smog and air pollution in United States, far exceeding industrial, commercial and residential sources. It accounts for one-third of all carbon dioxide (CO2), more than half of the carbon monoxide (CO) and nitrogen oxides (NOx), almost one quarter of the hydrocarbon emissions, over 30% of volatile organic compounds (VOCs), and over 20% of particulate matter (PM emissions) in the U.S. In total, motor vehicles can emit up to 40 hazardous air pollutants.

More than 60 percent of transportation-related emissions come from gasoline-powered private passenger vehicles and the remainder from diesel vehicles, construction equipment, aviation, shipping and other transportation activities.

Clean air is imperative to public health and a strong economy. State and federal clean air standards have reduced pollution that causes illness and death, contributing more than $2 trillion in economic and health benefits.

The National Ambient Air Quality Standards (adopted by the U.S. Environmental Protection Agency (EPA)) establish maximum levels for ozone, particulate matter and other air pollutants. Massachusetts’ air does not meet the standard for ground level ozone, so the Commonwealth, in accordance with the U.S. Clean Air Act, must implement programs that will reduce ozone levels.

Testing motor vehicles through the Massachusetts Vehicle Check Program helps ensure that vehicles run as cleanly as they were designed. If an emissions test shows a problem with the emissions control system, the vehicle’s owner is required to make the appropriate repairs.

What You Can Do

You can do your part to improve air quality in Massachusetts by maintaining your vehicle on a regular basis: have the engine tuned and the oil changed according to the manufacturer’s guidelines, watch for tell-tale signs of potential problems with the emissions control system of your vehicle, such as your “Check Engine” light staying illuminated, or black or bluish smoke coming from the tailpipe, and take note of a sudden decrease in your vehicle’s gas mileage.

To learn more about the quality of Massachusetts’ air, as well as programs and initiatives in the Commonwealth, visit the MassDEP website.

Safety

Safety is an equally important part of the Massachusetts Vehicle Check Program. A broken taillight, cracked windshield, defective suspension component or other defect can make a vehicle unsafe to drive. That’s why it’s important to make sure your vehicle is always in good repair, not just when you’re going to have your vehicle inspected. Fourteen key components of your vehicle are evaluated during the safety inspection. During the commercial inspection, over 70 items are subject to a thorough inspection meeting federal standards to ensure that commercial vehicles are in safe operating condition.

Vehicles listed below must receive the following types of emissions tests each year, in additional to mandatory safety tests for all registered vehicles:

On-Board Diagnostic (OBD) Test:

Model years 2010 and newer passenger cars, trucks and SUVs

Model years 2010 and newer light-duty diesel vehicles (with a Gross Vehicle Weight Rating or "GVWR" of 8,500 pounds or less)

Model years 2010 and newer medium-duty diesel vehicles (with a GVWR of 8,501 to 14,000 pounds)

Model years 2010 and newer medium-duty non-diesel vehicles (with a GVWR of 8,501 to 14,000 pounds)

Opacity Test:

Model year 1984 and newer, medium- and heavy-duty diesel vehicles (with a GVWR of 10,001 pounds or more) not subject to an OBD test

OBD Testing

On-board diagnostics (OBD) inspections are an important part of the Massachusetts Vehicle Check Program. No one wants to drive a vehicle that is wasting fuel or polluting. An inefficient engine or emissions control system adds pollutants to the air in our region and reduces a vehicle’s fuel economy.

The OBD test typically takes about three minutes. The inspector connects your vehicle's on-board computer to an analyzer in the station, and then downloads engine and emissions control data. The analyzer relies on the self-checks the vehicle’s OBD system makes of several functions:

Communication. Does your vehicle’s OBD system communicate with the analyzer? If your vehicle’s OBD system cannot communicate with the station’s analyzer, the OBD system must be repaired before the emissions test can be completed.

Readiness. Is your vehicle’s OBD system “ready” to be tested? As you drive your vehicle, the internal OBD system checks the performance of various emissions-related components and systems. If the OBD system has not performed enough of these self-checks, your vehicle may not be ready for an emissions test, and the analyzer will return a “Not Ready” result.

When a vehicle fails or is turned away from the inspection because its OBD system is "not ready," this simply means that at the time it was presented for inspection, the vehicle’s OBD system did not have enough valid data stored to accurately evaluate the vehicle’s emissions control system. Certain common repairs or maintenance procedures can temporarily interrupt power from a vehicle’s battery to its OBD computer, leaving monitors “not ready” for an emissions test because the power loss cleared all diagnostic results from the computer’s memory. After power is restored, in order for the vehicle to be “ready” for an emissions test, the computer needs to monitor various driving conditions long enough to run the required number of checks again, determine whether emissions-related systems or components are performing correctly, and once again properly store this information.

Until the vehicle’s on-board computer is “ready” for OBD emissions testing, the vehicle will fail its initial inspection or be turned away from a re-test. There may be nothing otherwise wrong with the vehicle; the computer simply needs to complete its checks. One week of combined highway and city driving is normally enough to reset the system and provide an accurate reading of vehicle performance.

To pass the emissions test:

2010 and newer model year non-diesel vehicles may have a maximum of one “not ready” non-continuous monitor.

2010 and newer model year diesel vehicles receiving an OBD test may have a maximum of one "not ready" non-continuous monitor.

If the vehicle failed the emissions test with a catalytic converter-related diagnostic trouble code, the vehicle’s catalyst monitor must be “ready” to pass the re-test.

Diagnostic Trouble Codes (DTCs). Why does the OBD system turn on the Check Engine light? Diagnostic trouble codes indicate which vehicle systems or components are not performing as designed. Reviewing these codes is the first step in diagnosing an emissions-related problem. These codes, along with other information in the OBD system, help guide emissions repair technicians to faulty parts and help take the “guess-work” out of the process.

Check Engine Light. Is the Check Engine light (sometimes labeled as “Service Engine Soon”) turned on? When this light illuminated, it indicates that one or more components of your vehicle’s emissions control system is not working as it was designed to work, and repairs are needed. If the light does not turn on when the OBD system tries to turn it on, this problem must be corrected.

Emissions Test Results. The results of your emissions test are printed on the Vehicle Inspection Report (VIR), which the inspector will give you when the inspection is finished. The VIR provides information that a repair technician can use to diagnose and repair your vehicle before it adds more pollutants to the air. This will also save you from more expensive repairs down the road.

If your vehicle passes both its OBD emissions test and its safety inspection, it will be issued a new windshield sticker with a black number indicating the month of expiration. If a problem is detected during the OBD test, your vehicle will fail its inspection and will need to be repaired. It will receive a windshield sticker with a black R. When it passes a re-test, the black R sticker will be replaced with a black number sticker representing the month of expiration.

Common Reasons Vehicles Fail the Emissions Test

The most common causes of emissions test failures include:

Malfunctioning components that regulate fuel/air ratio, such as oxygen sensors

Exhaust gas recirculation (EGR) valves

Engine misfire

Catalytic converters

Evaporative controls, including poor-fitting gas caps

The VIR provides information that a repair technician can use to diagnose and repair your vehicle. This may also save you from more expensive repairs down the road.

Opacity Testing of Heavy-Duty Diesel Vehicles

"Snap acceleration opacity" tests are used for diesel trucks, buses and other heavy-duty vehicles (with a GVWR of 10,001 pounds or more) not subject to an OBD emissions test.

In this test, the inspector uses an opacity meter or “smoke meter” to measure the smoke from the vehicle’s exhaust pipe. The darker the smoke, the more the vehicle is polluting and the higher its opacity reading will be.

Readings from three acceleration “snaps” are averaged. The final average is compared to the emissions standard for the model year and type of vehicle. Newer vehicles have more sophisticated emissions controls, and must meet stricter standards.