How to Pass An Emissions Test

How to Pass an Emissions Test.

Emissions testing, also known as a smog check, is required in many parts of the country. The procedure helps ensure your vehicle meets the emissions standards set by the Environmental Protection Agency (EPA) and/or state governments. Exactly how often your vehicle must be tested depends on the requirements set by the state or local government. The same goes for which model year is exempt or subject to emissions testing.

There are two basic types of emissions tests: tailpipe and onboard diagnostics (OBD II). Which one your car must undergo depends on the requirements in your area, as well as the age of your vehicle.

With an OBD test, a scan tool is plugged into the vehicle’s diagnostic port. That allows the technician to communicate with the onboard computer to ensure it isn’t flagging any emissions-related problems. OBD tests are only performed on model year 1996 and newer vehicles.

A tailpipe test, on the other hand, requires inserting an exhaust gas analyzer into the car’s tailpipe. The analyzer measures the levels of hydrocarbons (HC) and carbon monoxide (CO), both of which are pollutants, as well as harmless carbon dioxide (CO2) and oxygen.

Many locations also check levels of the pollutant oxides of nitrogen (NOx).

Passing an OBD test

You’re in luck if your location only requires an OBD test. There are just a couple of things you’ll need to check before heading to the emissions station.

Make sure the “Check Engine” light is off

Once again, your car will not pass an emissions test if your “Check Engine” light is illuminated. Make sure to address this issue and resolve the problem that triggered before you go in for testing.

Ensure all the monitors have run

Your car’s computer runs self-tests known as “monitors” on emissions-related systems. During an emissions test, a smog technician will check that all (or nearly all, depending on local requirements) of these monitors have “run” successfully.

The monitors are reset whenever the battery is disconnected. Clearing diagnostic trouble codes (DTCs) from the computer’s memory also resets the monitors. If either has been done to your car recently, you’ll want to be sure the monitors have run before emissions testing. If they have not, your car will be given a “not ready” test result, rather than passing or failing.

You can check whether the monitors have run using a scan tool or code reader, if you have one. Otherwise, you’ll want to drive the vehicle at various speeds (both on city streets and the highway) for an extended period of time. That way, you’ll have a better chance of being ready for emissions.

How long does a smog check take?

A smog check typically takes more or less 30 minutes. This can vary depending on the number of vehicles in line and whether or not you were able to schedule your vehicle for an appointment ahead of time.


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