Basic OBD2 Card Reader, plug it into your car’s OBD2 port and read out all standard error codes (and clear them if you like). Works just fine, but unlike fancier (and more expensive) units, you will need a code reference (easily downloaded from the web, I can print it for you if you like) in order to interpret the codes. A handy item to keep in your glovebox.
$10, cash, in person meetup in Catalina/N Oro Valley.