I'm just a girl with a mercedes and don't pretend to know much! My question is simple. I own a 2002 Mercedes C240. Do "fault and or malfunction codes ALWAYS show on the display, or are some, for whatever reason hidden only to be found once a mechanic "plugs you into the computer?"
I was quoted a price of $114.00 to "pull" the codes, but I don't see that I have any showing on my display. I just don't want to pay a mechanic $114 for him to tell me, "you have no malfunctions or fault codes". Duh!!
It's always best not to pretend to know something.
You don't have to go to a mechanic with your car to have codes read. Some auto parts stores will do it as well as Aamco. They will use a regular OBD-II reader that you can buy if you like for about $35 on Amazon (there are lots more expensive ones). When you read the codes you get alphanumeric displays like "P0302" and then you look them up in a table to translate them, the tables are posted on the forum or you can just search for them.
The malfunctions that come up in the display (such as low coolant, lamp malfunction, etc.) are not related to diagnostic codes.
For $114 the mechanic is probably tying into the diagnostic port under the hood and scanning all car systems; this is a broader diagnostic than simply plugging in an OBD-II reader to the little port under the dash. If the car is running fine and the check-engine light is not on, then there is no need to check for codes (or run diagnostics) except to help the mechanic make his boat payment.
Hope that helps. Also, if you click user cp and edit details you can add your vehicle and location to your profile, that's useful and you may find someone near you that would do the scan for free or show you how to use a code reader if you bought one, that's one of the good things about a forum.
Take care and enjoy the ride,