Skip the auto shop - Our mechanics make house calls

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

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.

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

Veteran and Military Driver Laws and Benefits in Idaho
The state of Idaho offers a number of benefits and perks for those Americans who have either served in an Armed Forces branch in the...
Auto Safety Tips
Driving is more than a way to get from point A to point B. Owning and driving a car can also be a highly enjoyable experience. Whether a person is driving...
P0291OBD-II Trouble Code: Cylinder 11 Injector Circuit Low
P0291 code definition When your vehicle’s PCM registers the P0291 code, it means that a voltage reading came from the fuel injector circuit – for cylinder number 11’s fuel injector –...


Related questions

Q: Where is the plug in for the code reader?

Your vehicle's OBD connector is located on the driver's side of the vehicle underneath the dash to the right of the steering column just above the gas pedal.

Q: Cost for transmission replacement

Re-manufactured transmissions for this vehicle cost in the neighborhood of $3,000, not including installation. Prior to deciding to re-build the car's existing transmission (a good, lower cost option) or replacing it with a re-manufactured unit (a higher cost option), the...

Q: Loud bog noise will not excellerate with no codes in computer

Just because the computer does not have any codes does not mean one of the sensors is not reading correctly. If you are using an oil bath type air filter, it may have contaminated the mass air flow sensor with...