The Check Engine light on your car is both useful and infuriating. You know something is wrong (which is good!), but you don’t know what. Rather than taking your car all the way down to your mechanic, you can get a pretty good idea what’s wrong with your car with a simple OBD-II adapter.

Every car sold in the US after 1996 has an OBD-II port that you can use to connect your car to your phone. This is the same port that a mechanic will connect to in order to find out what’s wrong with your car when the Check Engine light comes on. For a long time, you needed special hardware to use it, but cheap Bluetooth OBD-II adapters (and your cell phone) have made it easy to do it yourself.

There are several ways to diagnose your check engine light, but we’re going to use an app called Dash. This app lets you store important information about your car, track your driving and, as a bonus, diagnose check engine lights. It’s available for Android and iOS, so download it before moving on. If you’ve never used an OBD-II adapter before, check out our guide here to get set up.

RELATED: How to Make Your Car Smarter with an OBD-II Adapter

Turn on your car and let your OBD-II adapter pair to your phone. Open your Dash app and tap the car icon along the bottom to open your Garage.

Scroll to find the car you’re connected to right now (if you have more than one), then tap on it.

Underneath the picture of your car (if you have one), tap the Engine Alerts button.

If Dash detects an error code it can diagnose, it will display information about it here. It will also give you an estimate on how much it will cost to fix it. It will even search for mechanic shops in your area that you can take your car to.


Some error codes that a check engine light can throw may indicate several issues, so this isn’t a foolproof method. Some things you may be able to fix yourself—for example, if you lose your gas cap, you’ll get a check engine light, but replacing a gas cap is easy to fix. If it’s a complicated or delicate repair job, you may be better off taking it to a professional. In that case, Dash can at least help you shop around and find a reasonable price for the job.

Profile Photo for Eric Ravenscraft Eric Ravenscraft
Eric Ravenscraft has nearly a decade of writing experience in the technology industry. His work has also appeared in The New York Times, PCMag, The Daily Beast, Popular Science, Medium's OneZero, Android Police, Geek and Sundry, and The Inventory. Prior to joining How-To Geek, Eric spent three years working at Lifehacker.
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