Recurring Check Engine SLK230
 

I have a 2001 SLK230. I have taken my car to the dealer twice because the check engine light was on. The first time they said it was the O2 sensors. The second time, they said it'd be another $1200 and when I said forget it, the comp'd the charges. I didn't even make it home and the Check Engine light came on again. I called to ask what the code was this last time and they told me there wasn't a code. So I'd like to take it to Autozone because they'll read it and check the code so I can educate myself on this before going back to the dealer and getting scr wed because I'm a female. Where is the place to plug in the diagnostic tool on the 2001 Mercedes SKL230? Any assistance would be appreciated.
:gorgeous:

:help:

I beleive by fed mandate it must be either behind the ash tray, below the drivers side knee space or in the engine compartment.

On my 99' E300 it is above my left knee under the drivers side dash.