How to Read OBD-II Codes With a Scanner

Reading your own trouble codes takes about a minute and saves a diagnostic fee. Any OBD-II scanner — from a $20 reader to a phone-app dongle — will do it on any car sold in the US from 1996 onward.

What you’ll need

An OBD-II scanner or a Bluetooth dongle with a phone app (see our best OBD-II scanners)
Your vehicle (engine off to start)

Step by step

Find the OBD-II port. It’s a trapezoid-shaped, 16-pin connector — usually under the dashboard on the driver’s side, near the steering column.
Plug in the scanner firmly. For a Bluetooth dongle, also pair it with your phone app.
Turn the key to “on” (dash lights up) without starting the engine — or start the engine if your scanner requires it.
Select “Read codes” (sometimes “Scan” or “Trouble codes”) in the tool or app.
Write down every code, including pending codes. A code looks like P0420 — one letter and four digits.

What the code letters mean

P — Powertrain (engine, transmission, fuel, emissions). The most common.
B — Body (airbags, lighting, comfort systems).
C — Chassis (ABS, brakes, steering).
U — Network (module communication).

Look up what your code means

Enter the code in our code database for the plain-English meaning, a can-I-drive severity rating, the most likely causes ranked by likelihood, and DIY-vs-shop repair costs.

Should you clear the code?

Not until you’ve fixed the problem — clearing it only turns off the light temporarily. When you’re ready, here’s how to clear a check engine light the right way.