Requirements for Passing CT Emissions

by Johnno CaryUpdated August 06, 2023
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The state of Connecticut is one that requires emissions inspections on most cars, especially older vehicles, in order to receive vehicle registration for the vehicle from the Department of Motor Vehicles (DMV). It is a service that the vehicle owner must pay for, which measures the chemicals and emissions of a car in an effort to regulate air pollution and maintain a level of air quality in each state. The motorist is also responsible for selecting the emissions test center, an auto-repair shop that is certified by the state to perform the Connecticut emissions tests. If the vehicle fails the vehicle inspection report, it must be taken to a certified emissions repair facility, where the repairs must be made and a retest eventually reissued. Fortunately, there are a few things that you can do in order to ensure a passing vehicle emissions test.

The Gas Cap

the gas cap test will determine if gas is escaping the tank through the gas cap. You pass the state emissions test if the cap seals and you fail if it doesn’t. Inspect the gas cap for cracks, damage to the seal, or missing parts. Take the vehicle to an auto-parts store, the dealership you bought it from or a mechanic to purchase a cap that properly fits your vehicle. The gas cap cannot be a makeshift cap from another container, cloth material made to fit the tank opening or any other object that is not an official gas cap.

On Board Computer

This test is done on vehicles manufactured after 1996. The on-board diagnostics (OBD)computer is the component that monitors your car and signals trouble with a light that is visible on your dashboard. Most people know it as a “check engine” light. If yours is on prior to the test, your chances of passing the emissions standards test are greatly reduced. Have a mechanic hook your vehicle up to a diagnostic machine that will tell you what the problem is. Some auto-parts stores will perform the test free of charge.

Mufflers and Tail Pipes

Cars manufactured before 1996 will be put through a treadmill-like test called an Acceleration Simulation Mode. During the test, a sensor is placed within the tailpipe. To pass this test, have your tailpipe inspected for leaks and damage that may affect the emissions reading. Have it replaced before the test if necessary. The Pre-conditioned Two-speed Idle Test is also performed in the same way on vehicles that were made before 1996.

Catalytic Converter

All vehicles must have a catalytic converter present. Without one, the vehicle will not pass inspection. The catalytic converter is commonly located underneath the car, just before the muffler. You may have to ask a mechanic to help you find it. Do this research before you buy a used car as well. In Connecticut, the person who owns the vehicle without a catalytic converter is responsible for putting one on the car before it can be registered. You cannot pass an emissions test until the converter is properly placed.


Connecticut general statutes also allow a few exemptions to the CT emissions test, for example you do not need an emissions or smog test if your car is less than four model years old. Other exempt vehicles from the Connecticut emissions program include diesel-powered school buses (type ii), electric vehicles, motorcycles and agricultural equipment.

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