The "emissions test" is actually a series of tests. A passing result is necessary for most of these, but a few are currently just advisory. In addition to the I/M 240 dynamometer test (for 1982 and newer vehicles) or the two-speed idle test (for 1981 and older vehicles, and heavy duty trucks), elements of the emissions test are as follows:

Pretest Safety Check

As the vehicle enters the building, a brief check around the vehicle is made to make sure there are no visible problems that would make it unsafe to test. The inspector will look for obvious fluid leaks, worn tires, etc. If the vehicle is rejected from testing for safety or other reasons, you will be given a form stating what condition(s) must be corrected before the vehicle can be tested.

Visual Inspection of Emissions Equipment

On 1975 and newer vehicles, the following equipment is checked to make sure it is installed, intact, and in apparent working order:

gas cap
catalytic converter
air injection system
O2 sensor system
fuel filler restrictor
"check engine" light

Vehicles not originally equipped with these items are not required to have them. Vehicles that were originally equipped with any of them must have them in place in order to pass the emissions test. Gray market vehicles and custom built vehicles must have components appropriate to their model year, or must present evaluation paperwork from a state Emissions Technical Center.

Chlorofluorocarbon (CFC) Leak Check

Vehicles 1994 and older that are equipped with air conditioning are checked for CFC leakage from the air conditioning system. This test is advisory only.

Check Engine Light

This is a malfunction indicator and/or maintenance reminder light, depending on make and model of the vehicle. It may say "check engine," "service engine," or "emissions," or may simply contain an image of an engine. A malfunctioning check engine light is noted on the vehicle inspection report each motorist receives at the end of the emissions testing procedure. However, effective April 1, 2003, it is no longer a criteria for failing the emissions test. This is now advisory only.

Opacity (Smoke) Inspection

All vehicles are checked for the presence of visible smoke. More than five percent opacity for a duration of 5 seconds or longer will cause a vehicle to fail. (Smoke failures are not subject to the $75 and $715 repair limit.)

Onboard Diagnostics (OBD)

Beginning with 1994 models, some vehicles have been equipped with standardized computer-controlled OBD. Beginning with 1996 models, the OBD interface (a pigtail plug) was standardized on most models. 1994 and newer vehicles are checked for OBD computer codes. The result of the OBD test is advisory only.

Gas Cap Pressure Test

Gas caps on 1975 and newer vehicles are tested for leakage. The cap is removed from the vehicle and attached to a pressurization device. Gas caps that do not have an adequate seal allow hydrocarbon (HC) vapors (raw gasoline) to escape into the atmosphere. Failing this test will cause your vehicle to fail its emissions test. You will need to replace the cap and return your vehicle to an emissions center for a complete retest, not just a gas cap retest. The state requires a complete retest because a vehicle may perform differently once a properly sealed cap is in place. This is particularly true for computer-controlled vehicles.