Well, a few simple facts on your cars CE lamp warning.

First of all, a CE warning lamp activation is to let the driver know that a fault has been detected by the Emmissions control module in your car. The CE lamp does not store a code , it simply alerts you that the Emmissions Diagnostic Module has detected a system fault that will adversly effect the cars emmissions output beyond the Standard DOT legal mandates and that this fault/s has been recorded/stored in the Module and can be retrieved in the form of a Flash Formated code.
Secondly, you do not have to get a scanner or go to the Dealer to get this stored fault code. Your particular chassis has a built-in code access initiation LED/SW right in front of the battery that allows the owner to find out what the offending code/fault is.
SO, you do not have to build a tool or any of that jazz, b/c Mercedes has already done that for you......it is a Standard Feature that comes with the car.
But, how does one do this code access ?????
Simple.... There is a small rectangular Black Box in front of the battery..[ this is the owner access Diagnostic Box]..lift the lid and press /hold the button in for 2 seconds and release it....[ like one would do with setting a clock or any other digital home device ] ....upon release, the little red LED lamp next to that button will Flash back the code for you. You just count the amount of Flashes and post that info and we will tell you what this neat little Detection Device has found to be out of Normal .... do this a couple of times in case there is more than one stored code. Each code will have a different number of Flashes, in sequence.............so, you may find that you have 4 flashes the first try , and maybe 5 on the second try...you will then post for us that you have found the codes to be 4 and 5 in this example.
That's all....simple.

Now , if you had some serious Engine mangement problems [ like skipping and No Start, etc], or maybe an operating system failure, we could also tell you to how to build a Led tool to diagnose those OTHER modules on your car from that same BOX...but they have NOTHING to do with a CE lamp, so we will not go there or do that as your concern is only the CE Warning lamp.
...but if you did have serious other operating problems , we would go so far as to let you know how to do that also. [ with a simple homemade tool]

__________________
A Dalton