Skip the auto shop - Our mechanics make house calls

How Is the OBD Used During a State-Required Inspection?

obd test

If you live in an area that requires emissions testing each year, you’ll be required to go through a two-part test. The testing facility will do two things: they’ll measure the gases in your exhaust via a tailpipe test, and they’ll check your OBD (On-Board Diagnostics) system. What role does the OBD system play here? Why is a check of the OBD system needed if the facility conducts a tailpipe test?

Two reasons for a two-part test

There’s actually a very simple reason why the testing facility in your area will require an OBD test in addition to a tailpipe test. Contrary to popular belief, the OBD system does not measure gases produced other than oxygen. A tailpipe test is needed to analyze the different gases being produced and ensure that your car is within limits set by the government.

The second reason is tied to the first. A tailpipe test only checks for gases in your emissions. It can’t assess the health of your emissions control components. That’s what the OBD system does – it monitors your emissions equipment, such as the catalytic converter, oxygen sensor, and EGR valve. When a problem with one of these components occurs, the car’s computer sets a temporary code. If the problem is detected more than once, the computer turns on the Check Engine Light.

What an OBD system does

The OBD system does more than just light up when a part has failed. It’s able to detect progressive deterioration of your car’s emissions control components. This helps avoid potentially serious damage to the car, but also ensures that you’re able to replace failed emissions control equipment before the car begins creating serious pollution.

If the Check Engine Light is on in your dash, your car will not pass the emissions test, as there is a problem that will need to be repaired first. However, your car may not pass testing even if the Check Engine Light is not on, particularly if you fail the gas cap pressure test.

The statements expressed above are only for informational purposes and should be independently verified. Please see our terms of service for more details
Icon-warranty_badge-02

Skip the repair shop, our top-rated mechanics come to you.

At your home or office

Choose from 600+ repair, maintenance & diagnostic services. Our top-rated mechanics bring all parts & tools to your location.

Fair & transparent pricing

See labor & parts costs upfront, so you can book with confidence.

12-month, 12,000-mile warranty

Our services are backed by a 12-month, 12,000-mile warranty for your peace of mind.

Get A Quote

Need Help With Your Car?

Our certified mobile mechanics make house calls in over 2,000 U.S. cities. Fast, free online quotes for your car repair.

GET A QUOTE

More related articles

P0121 OBD-II Trouble Code: TPS "A" Circuit Range Performance Problem
P0121 code definition Throttle Pedal Position Sensor/Switch (TPS) A Circuit Range Performance Problem What the P0121 code means P0121 is a generic OBD-II code which indicates that the Engine Control...
P0240 OBD-II Trouble Code: Turbocharger Boost Sensor B Circuit Range/Performance
P0240 code definition Turbocharger Boost Sensor B Circuit Range/Performance What the P0240 code means P0240 is an OBD-II generic code triggered when the Engine Control Module (ECM) detects the intake boost...
Rules of the Road For Iowa Drivers
Driving on the roads requires knowledge of the rules, many of which are based on common sense and courtesy. However, even though you know the rules in...


Related questions

Q: 2 major issues

The code P0453 is for the purge control valve; it's most likely bad and needs to be replaced. The ticking noise is possibly the oil pressure dropping too low at idle and the camshaft followers are getting noisy. Have the...

Q: How Is the OBD Used During a State-Required Inspection?

State inspections vary from state to state and you should get any detailed inspection guidelines from the state you reside in. This article is for general guidelines of what the inspection of the vehicle onboard diagnostic (OBD) system is used...

Q: Where is the starter on a 2009 Jeep Patriot

On your car, the starter is below the air cleaner box and air tube. You have to remove those, as well as other components to access the starter. Once you have accessed the connections to the starter, test for power...