OBD ports can be notoriously difficult to find! The OBD port in a 2010 Ford Fusion is under the steering wheel to the left above the foot rest. You’ll probably need to open the driver’s side door and squat down in order to see it.

Some OBD ports have a plastic cover in front of them that says OBD. If your Fusion has this, pull the plastic cover down to access the port. Otherwise, just plug in your Onboard Diagnostics II (OBD-II) scanner.

Turn on the car without switching on the engine to power the scanner tool. Then, press Scan on the device so it begins running diagnostics. You’ll see a Diagnostic Trouble Code (DTC), appear on the screen. Read these codes to see what’s going on with your Fusion. Here’s what each character in the code means:

Ideally, the code will tell you why the Ford’s check engine light came on. If you’re still confused, refer to the scanner’s manual or search for the code online. You can also take your Fusion to a trusted mechanic and explain what code the scanner is throwing out.

MORE: How to understand car OBD codes