What Is the On-Board Diagnostics (OBD) System? | YourMechanic Advice

What Is the On-Board Diagnostics (OBD) System?

Your car contains a vast number of different systems, all of which must work in harmony to ensure proper operation. There must be a way to monitor your ignition and emissions systems and the On-Board Diagnostics (OBD) is a computer that keeps tabs on what’s going on with your vehicle.

What the OBD system does

Simply stated, the OBD system is an on-board computer that communicates with other systems, including the ECU, TCU and more. It monitors the performance of your ignition system, engine performance, transmission operation, emissions system operation and more. Based on feedback from sensors around the vehicle, the OBD system determines if everything is working properly, or if something is beginning to go wrong. It’s advanced enough to warn drivers before a serious problem occurs, often at the first symptom of a failing component.

When the OBD system identifies an issue, it turns on a warning light in the dash (generally, the Check Engine Light), and then stores a trouble code (called a DTC, or diagnostic trouble code). A mechanic can connect a scan tool to the OBD II connector under the dash and read this code. This provides the information needed to begin the diagnostic process. Note that reading a code does not necessarily mean that the mechanic knows immediately what has gone wrong, but that the mechanic has a place to begin looking.

As a note, the OBD system also determines whether your car will pass emissions testing. If the Check Engine Light is on, your car won’t pass the test. There’s also a chance that it won’t pass even if the Check Engine Light is not on.


Next Step

Schedule Oil Change

The most popular service booked by readers of this article is Oil Change. 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 Oil Change reviews

Excellent Rating

(21,049)

Rating Summary
19,750
838
175
85
201
19,750
838
175
85
201

Shawn

11 years of experience
121 reviews
Shawn
11 years of experience
Toyota Camry - Oil Change - Lancaster, Pennsylvania
On time. Explained everything that was done and noted an issues that had occurred from a prior oil change that I could take up with the previous garage. I highly recommend Shawn.
Mercedes-Benz C300 - Oil Change - Norristown, Pennsylvania
Arrived on time and was very professional. Helped me diagnose a potential alternator issue. Was very polite and easy to work with.

Pardeep

20 years of experience
812 reviews
Pardeep
20 years of experience
BMW X5 - Oil Change - Santa Clara, California
Pradeep was punctual, informative, knowledgable and professional throughout . I would highly recommend him .
Ford Expedition - Oil Change - Saratoga, California
Called and came much sooner. Did a prompt and neat job. Friendly and very easy to communicate with. Recommend, based on my experience.

Stacy

23 years of experience
281 reviews
Stacy
23 years of experience
Audi A6 Quattro - Oil Change - Atlanta, Georgia
Very, very kind and thoughtful young man! I was very pleased with his demeanor and class! Quite an asset to your Co. Also a good mechanic, thank you for sending him!
Scion xA - Oil Change - Atlanta, Georgia
Quickly rotated my tires & oil change. Let’s me know what is going on with my vehicle during the process. Highly recommended.

Tinashe

12 years of experience
447 reviews
Tinashe
12 years of experience
Mazda 3 - Oil Change - Atlanta, Georgia
I have used Tinashe multiple times for my vehicle service. He is always quick and thorough with his top-quality work. I have never been disappointed!
Ford F-350 Super Duty - Oil Change - Alpharetta, Georgia
Tinashe I feel did a great job as he listened to my request and handled what I needed done. I will be requesting him again.

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

How to Diagnose Your Car Problems If You Know Nothing About Cars
Learn how you can diagnose car problems like engine issues without using diagnostic tools or any prior knowledge about cars.
P1103 OBD-II Trouble Code: Mass Airflow Sensor in Range But Higher Than Expected
P1103 means there is an issue with the mass airflow sensor, likely due to faulty or loose wiring and connectors in the sensor, or an air leak.
P0426 OBD-II Trouble Code: Catalyst Temperature Sensor Range/Performance (Bank 1)
P0426 means there is a problem with the bank 1 catalytic converter, and could be caused be a faulty oxygen sensor or catalytic converter.

Related questions

Need a diagnostic.

Most shops charge an hour of labor for a diagnostic. The price for this hour of labor can range anywhere from $90.00 up to $120.00. If you have your diagnostic performed by a technician from YourMechanic you can get this...

Truck won't turn over

The battery should be load tested by a professional. Load testing can only be reliably performed on a fully charged battery. If the battery passes a load test be sure it is NOT a marginal pass in which case you...

The check engine light is on and it's say gas cap what price range am I lookin at to have it fixed

If you are referring to the warning light for a loose gas cap loose and/or Diagnostic Trouble Code P0442, a loose or defective gas cap is merely one possible reason for the warning light or the Code. You could have...

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