Pretest Safety Check
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.
Visual Inspection of Emissions Equipment
On 1975 and newer vehicles, the following equipment can be checked out to make sure it is installed, intact, and in working order:
- gas cap
- catalytic converter
- air injection system
- O2 sensor system
- check engine light
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, emissions, or may simply contain an image of an engine.
Your vehicle will be checked for the presence of visible smoke.
Onboard Diagnostics (OBD)
Beginning with 1994 models, some vehicles have been equipped with standardized computer-controlled OBD. Beginning with 1996 models, the OBD interface was standardized on most models. 1994 and newer vehicles are checked for OBD computer codes.
Gas Cap Pressure Test
Gas caps on 1975 and newer vehicles can be 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.