A few years ago I bought a Bluedriver obd auto scanner for $50. I used it a few times to diagnose warning codes on various cars. Yesterday on my Subaru Forrester the display lit up with numerous warning lights. Uh oh.
I plugged in the scanner and started the app on my cell phone. The scan identified the probable cause, displayed suggested approach to resolve and listed fixes that other users suggested worked for them.
I followed the recommended trouble shooting process, found the problem, corrected the cause and cleared the codes. All is well.