Welcome to the Connecticut Emissions Program

Why a vehicle specifically failed depends on the emissions test required for each vehicle, based on the model year, fuel type, and gross vehicle weight rating (GVWR).

  • Catalytic Converter (Visual Inspection) – All vehicles are subject to the visual verification of the catalytic converter; if one or more catalytic converters are missing from your vehicle, the emissions test will fail.

  • On-Board Diagnostic (OBD) Test – Failing the OBD emissions test can occur for one or more of the following:

    • The OBD system is commanding the Malfunction Indicator Light (MIL) to illuminate while the vehicle is running.
    • The OBD system readiness monitors are ‘Not Ready’, which indicates specific OBD systems have NOT completed their self-evaluating protocols, which can be caused by disconnecting the vehicle’s battery or intentionally resetting the OBD system.
    • The Diagnostic Link Connector (DLC) in a vehicle is missing, damaged or inaccessible.
    • The emissions analyzer cannot communicate with a vehicle (OBD communication failure).
    • Vehicle may also fail the OBD test for the MIL light not working.
    • The inspector performing the emission test must perform a visual verification of the MIL light. The light MUST illuminate with the key-on engine-off; if not, this indicates tampering with the light or a defective bulb or circuit.
  • Pre-Condition Two-Speed Idle (PC TSI) Test – 2007 and older non-diesel vehicles with the GVWR of 8,501 LBS to 10,000 LBS, receive the PC TSI test, which measures tailpipe emissions. Vehicles fail this test, for emitting excessive levels of one or both of the major air pollutants, carbon monoxide and/or hydrocarbons. During the PC TSI test, vehicles are subject to the Gas Cap Pressure Leak Test. If a gas cap fails the leak test, it means excessive amounts of fuel vapors are escaping into the atmosphere.

  • Modified Snap Acceleration (MSA) Opacity Test – This test applies to 1996 vehicles or 2006 and older diesel-powered vehicles with the GVWR of 8,501 LBS to 10,000 LBS. The MSA test utilizes an opacity meter measuring the smoke density emitted from the vehicle’s tailpipe. If a vehicle fails this test, it is emitting excessive levels of particulate matter (smoke).

If you need further clarification on why your vehicle failed, please call the motorist hotline at 1-888-828-8399.