How Can I Tell If the OBD System Is Working Correctly?

Today’s cars are far more sophisticated than they once were, and they require a computer to monitor and manage the various systems so that everything works together properly. This also gives you the means to determine if there’s something going wrong with your car. The OBD II system (On Board Diagnostic) is a system that allows a mechanic to communicate with your car’s computer and pull trouble codes in many situations. These codes tell the mechanic where the trouble is, but not necessarily what the actual problem is.

How to tell if the OBD is working

Determining if your OBD system is working is actually very simple.

Start with the engine off. Turn the key to "on," and then run so that the engine cranks. Watch the dash during this time. The Check Engine Light should flash on, and stay on for a brief period. It should then turn off. The brief flash on is the signal that the system is up and running, and ready to monitor your vehicle during operation.

If the Check Engine Light comes on and stays on, then there’s a trouble code (DTC) stored in the computer that indicates a fault somewhere in the engine, the transmission or the emissions system. This code should be checked by a mechanic so that an accurate repair can be made.

If the Check Engine Light does not flash and turn off (or if it never comes on at all), it’s a sign that there is something wrong with the system, and it must be checked by a professional mechanic.

Your vehicle will not pass annual testing without an operable OBD system, and you will also have no way of knowing if something is wrong with the vehicle.


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

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

B1971 OBD-II Trouble Code: Passenger Seatback Rearward Switch Circuit Short to Ground
B1971 means there is an error with the seatback rearward switch. This is most likely due to damaged electrical components or a bad switch.
P1101 OBD-II Trouble Code: Mass Airflow Sensor Out of Self Test Range
P1101 means there is an issue with the mass airflow sensor system. It is likely due to a faulty sensor, bad connectors, or an air leak.
B1915 OBD-II Trouble Code: Air Bag Driver Circuit Failure
B1915 means the air bag driver circuit has failed, likely due to defective wires or a faulty clock spring.

Related questions

Can I Look Up What Trouble Codes Mean?
When your Check Engine Light comes on (https://www.yourmechanic.com/services/check-engine-light-is-on-inspection) or flashes on the dash for you it is indicating there is a problem in one of the vehicle systems and has set a trouble code stored in one of the modules’...
What Types of Trouble Codes Cause Lights to Come On in My Dash?
Different vehicles have a different number of lights on the dashboard to warn you of problems, some with just a few basic lights while others have plenty to distinguish between different issues. This article will cover just the bright yellow...
Why doesn't anyone offer a quote for a compression or CLT test?
In almost all cases, individuals with engine faults are seeking resolution to an "acute" fault and not so much presenting with a "worn out" engine, that is one with low cylinder compression and cylinder leakage. A compression loss that is...

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