I'd say PA 3L SVT has it nailed. OBD-II specifies a standard set of engine management related codes, or the P-codes (for powertrains, such as P0171.)
Chassis codes are vendor specific. So when it comes to learning what the ABS, climate control system, or whatever the carmaker has tied up to the computers (yes plural) in the car, your local shop may not be able to read the codes.
And remember, if you are trying this at home, if you get a code, you need to know
why you got that code. The codes don't always just say, replace Bank 1 O2 sensor.
And if you have a mechanic working on your car, don't pay for guessing. Let them know that you are paying for their expertise, not guessing. If you want guessing, come to my house, and I'll start picking parts to swap
TB
