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Summary
  • How long does emissions testing take? You should probably allot 20 to 30 minutes for a smog check. That said, you can finish an emissions test in as fast as 10 to 15 minutes.sta
  • Emissions tests typically involve connecting a computer to your vehicle’s onboard diagnostics and conducting a tailpipe test.
  • This might sound quick, but if your vehicle fails the smog test, then you’ll need to make the necessary adjustments, modifications, or repairs, which will take more time.

Smog checks or emissions tests are mandatory procedures done to verify if a vehicle meets a state’s prescribed emissions standards. New to emissions tests? You might be wondering “How long does an emissions test take?”

You should probably allot 20 to 30 minutes for a smog check. That said, you can finish an emissions test in as fast as 10 to 15 minutes.  You should also anticipate the possibility of queues, especially during peak times. If you can, try to go on a weekday afternoon to save time.

This might sound quick, but if your vehicle fails the smog test, then you’ll need to make the necessary adjustments, modifications, or repairs, which will take more time. Most emissions test centers will give you an emissions report that indicates the necessary repairs. This can be as simple as changing your vehicle’s catalytic converter, spark plugs, or air filter, which usually takes a few hours at the shop.

Emissions Test Steps

An emissions test isn’t as simple as inserting a tube into your vehicle’s exhaust and revving the engine. After filling up the forms, the first thing a mechanic will do is check if your emissions control system is functioning as it should. These include the catalytic converter, the exhaust gas recirculation (EGR) system, and evaporative control system, among other components.

The mechanic will also check your vehicle’s gas cap if it’s properly sealed, since a leaking gas cap can cause fuel vapors to leak, which is a form of emission itself. The mechanic will also check your vehicle’s ignition timing using a specialized tool.

They will also check your vehicle’s check engine light. If this light is illuminated, then it means that your vehicle’s onboard diagnostic (OBD) system has detected an issue, which will immediately cause you to fail the test. Make sure you don’t have an illuminated check engine light before getting an emissions test. If you do, make sure to resolve the issue causing your vehicle’s check engine light to illuminate.

The emissions test personnel will then connect a scan tool to your vehicle’s OBD data link connector, which is typically underneath the steering wheel. This allows a computer to scan the vehicle’s OBD system.

The vehicle’s OBD system can typically detect if the engine has faulty oxygen sensors or other issues. If the scan tool detects that the OBD system has stored codes because of faulty components, then your vehicle is most likely not performing within specification and will cause your vehicle to fail the test.

The data link connector also checks various systems like the evaporative emissions system, ignition timing, and exhaust gas recirculation system, among others. In some states, this is as far as the smog test goes. In other states, however, your vehicle will still need to go through a tailpipe test where a hose is inserted into its exhaust. Vehicles made before 1996 and vehicles that don’t have OBD systems are required to conduct a tailpipe test.

This process typically involves revving the engine for a few seconds while a computer analyzes your vehicle’s exhaust gases. The emissions personnel will also inspect the underside of your vehicle for fuel leaks.

Once your test is finished, you’ll receive a Vehicle Inspection Report. The testing station will also electronically transfer the test information to your local Department of Motor Vehicles (DMV) so you can register your vehicle.

Why Are Smog Checks Important?

The Federal government is vowing to halve the country’s total emissions by 2030 as a response to climate change. The US has been the leading country when it comes to greenhouse gases for many years now. Aside from switching to electric and hybrid vehicles, part of its strategy includes having stricter emissions standards across all vehicle classes.

About The Author
Written By Automotive and Tech Writers

The CarParts.com Research Team is composed of experienced automotive and tech writers working with (ASE)-certified automobile technicians and automotive journalists to bring up-to-date, helpful information to car owners in the US. Guided by CarParts.com's thorough editorial process, our team strives to produce guides and resources DIYers and casual car owners can trust.

Any information provided on this Website is for informational purposes only and is not intended to replace consultation with a professional mechanic. The accuracy and timeliness of the information may change from the time of publication.

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