NWG Automotive Repair
State Vehicle Inspection
Why do we test?
Gasoline, which generally contains an additive such as ethanol, evaporates easily and is highly flammable. In a gasoline engine, a spark ignites the fuel, but the combustion process is inefficient. About one-quarter of the fuel actually powers the vehicle forward; the rest is consumed by friction and heat, or emitted as exhaust.
Diesel fuel is heavier, oilier, less evaporative and less flammable than gasoline. In a diesel engine, the fuel is ignited through compression of air in the cylinders. Because diesel fuel has a higher energy density than gasoline, vehicles that run on diesel tend to deliver far better fuel economy than gasoline vehicles.
Both gasoline and diesel fuel contain mixtures of hydrocarbons, which are compounds that contain both hydrogen and carbon atoms. In a “perfect” engine, oxygen from the air would convert all of the fuel's hydrogen to water, and carbon to carbon dioxide. But no combustion process is perfect, so both gasoline and diesel vehicles are equipped with emission control systems that reduce (but do not eliminate) pollutants that can be harmful to the environment or public health:
Nitrogen Oxides (NOx) and Hydrocarbons (HC) react in the presence of sunlight to form ground-level ozone or "smog," which can irritate eyes, damage lungs and aggravate respiratory problems. Symptoms include coughing, shortness of breath and difficulty breathing. Hydrocarbons also contribute to global climate change and many are considered hazardous air pollutants.
Carbon Monoxide (CO) reduces the flow of oxygen in the bloodstream and is of particular concern to people with heart disease.
Carbon Dioxide (CO2) is a “greenhouse gas” that traps the earth's heat and contributes to global climate change. Due to differences in their comparative fuel efficiency, diesel vehicles tend to emit less CO2 per mile than vehicles with gasoline engines.
Sulfur Dioxide (SO2) contributes to the formation of acid rain.
- Hazardous Air Pollutants (HAPs) are substances that the U.S. Environmental Protection Agency (EPA) considers dangerous or toxic. Motor vehicles can emit up to 40 of these pollutants, including 15 that are known or suspected to cause cancer. Of greatest concern are acetaldehyde, benzene, 1,3-butadiene, formaldehyde, and polycyclic aromatic hydrocarbons (PAHs). Learn more about air toxics from motor vehicles.
SafetySafety is an equally important part of the Massachusetts Vehicle Check. A broken taillight, cracked windshield or a defective horn might not seem important, but any one of these or many other conditions can make driving unsafe. That's why it's important to make sure your vehicle is always in good repair, not just when you're going to have it inspected. The safety inspection looks for specific criteria.
Medium- and heavy-duty diesel vehicles (with a GVWR of 10,000 pounds or greater) not equipped with OBD systems
The Massachusetts Vehicle Check on-board diagnostic (OBD) emissions test is designed to ensure that your vehicle keeps running as cleanly as it was designed to run, which in turn protects the air we breathe.
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 checks several OBD system 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 your vehicle drives, the 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 is “not ready” for an emissions test.
To pass the emissions test:
- 2002 and newer model year vehicles may have a maximum of one (1) “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 retest.
Diagnostic Trouble Codes (DTCs). Why would the OBD system turn on the Check Engine light? These indicators are diagnostic trouble codes that indicate which 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 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 is turned on, it indicates that one or more components of your vehicle's emission 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.
The results are printed on the Vehicle Inspection Report (VIR), which the inspector will give you when the inspection is finished.
If your vehicle passes both its OBD emissions test and its safety inspection, it is issued a new sticker. If OBD detects a problem with your vehicle (generally indicated in advance by an illuminated "Check Engine" or "Service Soon" light), your vehicle will fail its inspection and will need to be repaired.
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
Evaporative controls, including poor-fitting gas caps
Sometimes, a vehicle will fail or be turned away from inspection because its OBD system is "not ready." This simply means that the OBD system did not have enough valid data to evaluate the vehicle's emissions control system. This may be because the vehicle's battery was disconnected recently, perhaps while repairs were being made to the alternator, starter, electrical system, engine or transmission. Usually, a week of combined highway and city driving will reset the OBD system so that it will be ready for testing.
The VIR provides information that a repair technician can use to diagnose your vehicle's problem, fix it before it causes more air pollution, and spare you from more expensive repairs down the road.
For more detail about emissions inspections, please review the MassDEP Vehicle Emissions Inspection Regulations.
Safety inspections typically take about 12 minutes. In a safety test, the inspector looks for or tests 14 key areas:
- Certificate of registration
- License plate(s): For more information about the license plate inspection requirements, click here. For answers to frequently asked license plate questions, click here.
- Vehicle Identification Number (VIN)
2. Brake Tests
- Sound horn to test for adequate signal
- The horn must be securely fastened to the vehicle
- Windshield wipers and washer
- Window tinting: For more information about the window tint inspection requirements, click here.
- Rear view mirror
- Mirrors (General)
- Tail Lights
- Directional (turn signal lights)
- Head light aim
- Hazard lights/Reverse lights/License plate light(s) and Reflectors
- After Market Lighting
12. Seat Belts
14. Fuel Tank Cap
- Accepted here: