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

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.


Next Step

Schedule Check Engine Light is on Inspection

The most popular service booked by readers of this article is Check Engine Light is on Inspection. Once the problem has been diagnosed, you will be provided with an upfront quote for the recommended fix and receive $20.00 off as a credit towards the repair. YourMechanic’s technicians bring the dealership to you by performing this job at your home or office 7-days a week between 7AM-9PM. We currently cover over 2,000 cities and have 100k+ 5-star reviews... LEARN MORE

SEE PRICING & SCHEDULING

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

Recent Check Engine Light is on Inspection reviews

Excellent Rating

(8,600)

Rating Summary
8,017
273
65
46
199
8,017
273
65
46
199

Dan

40 years of experience
1080 reviews
Dan
40 years of experience
Plymouth Grand Voyager V6-3.3L - Check Engine Light is on - Lawrenceville, Georgia
Mr. Dan Barber was quite patient, courteous and quite knowledgeable. From my observation, Mr. Barber appears to be quite professional.
Nissan Altima - Check Engine Light is on - Gainesville, Georgia
Dan is a super nice man that listens to your issue and does an easy to understand explanation so that you can truly take in, process and actually feel like you know what is going on with your vehicle and needed repairs. Honesty is what I felt I received. He wanted to make sure I was in a safe operating vehicle. His skill and knowledge level are exceptional. I will never use another car dealership for diagnostics or repairs. Thank You Dan!!!!!

Greg

23 years of experience
624 reviews
Greg
23 years of experience
Toyota Camry L4-2.4L - Check Engine Light is on - Phoenix, Arizona
Attention to detail and provided clear information to his findings. Acted in a Profesional manner throuout
BMW X5 - Check Engine Light is on - Chandler, Arizona
Greg was running a bit late due to business being busy but he comunicated with me very well, and let me know where he currently was and what time to expect him. Also he went above and beyond by showing me some small things that I could do myself to make my older BMW run excellent. Thanks Greg, appreciate your passion for your job

Keven

8 years of experience
187 reviews
Keven
8 years of experience
Subaru Impreza H4-2.5L - Check Engine Light is on - Spanaway, Washington
Very professional courteous respectful knowledgeable explains everything of the aspect of work and what needs to be done on the vehicle. Exceptional awesome amazing friendly and kind. 10+stars. I highly recomend friends and families if they need a experience mechanic is to ho to your mechanic and ask for Keven. Thanks again for an exceptional diagnostic repairs on my daughter vehicle. Very happy and pleased.
Hyundai Veloster - Check Engine Light is on - Tacoma, Washington
He is very informative, professional and friendly. He told us what was wrong with our vehicle in details, and gave us very helpful suggestions.

Brian

19 years of experience
138 reviews
Brian
19 years of experience
Nissan Juke L4-1.6L Turbo - Check Engine Light is on - Hampton, Georgia
Professional, knowledgeable, diagnosed problem very quickly. Provided me with feedback as to probable cause of the defect.
Chevrolet Trax - Check Engine Light is on - Covington, Georgia
Very professional/punctual & knowledgeable. I’d prefer Brian to repair my moms vehicle since I’ve established a rapport with him if at all possible when I’ve gotten my final quote that’s reasonable after choosing services/parts to perform the repair work.

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

Related articles

P0541 OBD-II Trouble Code: Intake Air Heater Relay 1 Low
P0541 means there is a failure on the #1 air intake heater relay circuit, likely due to a faulty wiring connection somewhere in the relay.
How to Troubleshoot a Clutch Pedal Sticking to the Floor
Clutch pedals in manual cars stay on the floor if there's a failed clutch release bearing, slave cylinder, clutch master cylinder, or clutch linkage.
How to Troubleshoot a Clutch That Won't Fully Disengage
A slipping clutch is a clutch that's not fully disengaging, which could be caused by a broken clutch cable, a hydraulic leak, or incompatible parts.

Related questions

Received a diagnostic code P0562.
The code you have indicates that there is low voltage to the powertrain control module. This is likely due to your battery being low on charge due to age. When the engine first cranks over it is a great strain...
ABS light on dash board
Hello. Since this could be a variety of potential issues, I would recommend hooking the car up to an OBD scanner to download any trouble codes that may have registered as a result of the light coming on. I would...
Service Engine Soon light driving problems
Any one, or more, out of a list of thousands of Diagnostic Trouble Codes could have caused your vehicle's Check Engine Light to illuminate. Even given your very well stated description of what occurred, no "one" of these many codes...

How can we help?

Our service team is available 7 days a week, Monday - Friday from 6 AM to 5 PM PST, Saturday - Sunday 7 AM - 4 PM PST.

1 (855) 347-2779 · hi@yourmechanic.com