Cars and trucks stuck in traffic can cause smog, which reduces air quality. For this reason, some states and cities require residents to have their vehicles tested for emissions.
According to the Washington State Vehicle Inspection Program, there are ways you can prepare for your emissions test at home. First, check the levels of engine fluids like coolant and oil. Then, make sure your gas cap is screwed on tightly. All vehicles have their gas cap tested (which can include a visual evaluation). Lastly, warm up the engine by driving the car around before heading to the testing facility, but keep the air conditioning and radio off.
It is unlikely that you could perform the actual emissions tests at home because specialized equipment is necessary. You can, however, know what tests to expect. If your car is year 1996 through the latest models, runs on gasoline and weighs under 8,500 lbs., you will typically get an on-board diagnostic test, or OBD, from your vehicle's computer. The OBD monitors your vehicle's major systems including the emissions control components. It is responsible for the "Check Engine" light that comes on when there is a problem with your vehicle.
If your car is a year 1995 and older, runs on gasoline, weighs under 8,500 lbs. and has two-wheel or part-time four-wheel drive, it will undergo an acceleration simulation mode test. This test employs a dynamometer, a machine the Environmental Protection Agency designates to provide a simulated road test for emissions. It is similar to a person receiving a heart stress test on a treadmill.
Vehicles that were made in 1995 or older, run on gasoline but operate at constant four wheel drive or weigh more than 8,500 lbs., undergo a two-speed idle test. This test requires the vehicle to be in neutral and for the engine to idle at 2500 RPM.
