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Q: What Emissions Tests Are Performed on My Car?

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What emissions tests are performed on my car?

A: The actual emissions testing process varies...

The actual emissions testing process varies considerably from one state to another, as well as with different vehicles. However, your OBD system will definitely be checked. You may also need a tailpipe test, a gas cap test, and a visual inspection of the exhaust system. Check your state’s specific DOT or DMV website to learn more.

Vehicle emissions tests check for several things. First, the actual tailpipe emissions are measured. The actual gases that are measured are hydrocarbons (HC), carbon dioxide (CO2), carbon monoxide (CO), oxygen (O2), and oxides of nitrogen (NOx).

The limits of these gases are mandated by either the federal government or your individual state. A growing number of states, and some countries, are adopting the more stringent emissions requirements similar to those in the state of California.

Basically, here's how your tailpipe emissions test should measure up. HC - low; O2 - low; CO2 - high; CO - low; NOx - low.

HC is fuel. We don't want any unburned fuel reaching the atmosphere where it can become smog.

The same goes for CO, which is a byproduct of the combustion process.

CO2 is a measurement of the efficiency of the combustion process, so we want this measurement to be high.

Oxygen, even though it's not a contaminant, should be low. We want as much oxygen as possible to react with the fuel inside of the engine to produce power. That also means we want as much of the fuel as possible to be converted into heat.

NOx is another byproduct of combustion. Higher combustion chamber temperatures mean more NOx production. NOx is reduced in two ways: catalytic converters and the EGR (exhaust gas recirculation) system.

Other emissions tests check your gas cap for its ability to hold pressure. Specifically, its ability to hold fuel vapors inside the fuel tank as it is being evaluated.

If you have recently failed an emissions test and need some assistance in getting your vehicle back up to snuff, consider having the car inspected by a qualified technician. A good-running car is essential not only for the environment, but for your daily needs, too.

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