Emissions Testing and Smog Check

Registering a vehicle in many states requires the vehicle owner to obtain emissions testing before vehicle registration can be completed. This is also called a smog check in some areas. States that require this are normally higher in population or have problems with air quality.


Many states provide an exemption for new vehicles during the first five years. Smog testing may be required yearly, in states like Massachusetts and New York, or every two years, in states like New Jersey and California. In some states, only certain counties will have an emissions testing requirement in place. However, falsifying a residential address to avoid testing can result in fines or legal action.


In addition, some areas require a vehicle safety inspection when registering or renewing a registration. To determine what regulations apply to you, contact your local Bureau of Motor Vehicles (BMV) or Department of Motor Vehicles (DMV). As a car buyer, the ability for the vehicle to pass an inspection can be a critical factor in the purchase. Ask the seller if a smog test was performed recently or if they have a smog check history for the vehicle. Sellers do not have to have the vehicle tested, but it can improve the chances of the vehicle selling at a solid price.


Common Smog Testing Failure Reasons


Most smog check or emissions testing stations will give you print out of the possible reasons your vehicle failed the test. You should receive a written of the results. This information can often be provided to a mechanic to determine the malfunction in your vehicle.


Common failures:


  • Missing exhaust system parts
  • Modified exhaust systems
  • Defective catalytic convertors
  • Defective oxygen sensor
  • Vacuum leak
  • Faulty EVAP – evaporative emission control system including poorly sealing gas cap
  • Faulty computer module for fuel to air ratio – rich fuel mixture
  • Carburetor issues in non-fuel injection engines – rich fuel mixture

You must have your vehicle tested at an approved, licensed inspection station. Stations are regulated by the state. If your vehicle fails emissions testing, do get it repaired and reinspected quickly. Most inspection agencies are required to retest for no additional fee for a period of 30 days. This can also vary by state, ask the station what policies apply to your state.


Quick Tip


Many car owners will find that adding a can of fuel line cleaner to their gas tank will improve their vehicle's performance during emission testing. Do follow the vehicle manufacturer's recommendations for fuel additives and the directions for the cleaner you are using.


To obtain benefits, the additive is added to a full tank of gas and the full tank must be run through the vehicle. This will not help you pass a smog check if you have major problems with your vehicle, but can help with borderline cases.