The codes can be had from the pushbutton controller on most models. I wrote an article describing the technique on a 210 chassis car E320: http://www.continentalimports.com/ser_ic40142.html
They should be similar to yours. If you read the article and want to try I will list the method here for the S420 just in case it is different from the article.
Turn ignition on, Set left display "Hi" set right display "Lo", within 20 secs press the "Rest" button and the "EC" button simultaneously for greater than 5 secs. The LED in the "Recirc" button flashes and the display window reads "Off". Press the right "Auto" for greater than one second. If there are not DTCs (diagnostic trouble codes): "E" is displayed in the left side of the display window and "FF" is displayed in the right side.
If DTCs are stored in memory : Ebl is displayed in the left side and the DTC (e.g. 416) is displayed in the right side.
By pressing "Auto" the next code will appear. Do this till all codes are read.