O.k.there is a bulletin on this fault for this model here.My guess is your seeing the message "Start Error".The bulletin from Mercedes is bulletin number T-B-80.57/32.Here is what the bulletin states:
Model Year 2000 to 2005 Engine Will Not Start and Fault Message "Start Error" Appears in Instrument Cluster If you receive customer reports in the above model vehicles of the engine not starting and the message "Start Error" appearing in the instrument cluster, the drive authorization module may need to be replaced. The drive authorization module (FBM) listed in the Parts Information section below now contains modified software to correct this condition. Note: This occurs when circuit 15 is truncated after the engine control unit sends a drive authorization system inquiry to the drive authorization module. If circuit 15 is switched off during this inquiry or is interrupted before the drive authorization module can respond, the same variable code is again used for the next circuit 15 cycle, as the drive authorization module has saved the previous inquiry. This results in the engine not starting for this key cycle. To resolve, remove the old FBM control unit as per WIS instruction AR54.21-P-1300GH and replace FBM control unit with part number listed in the parts information section below. Note: Step 6 of AR54.21-P-1300GH checks whether the vehicle can be started with all keys. Ensure that all keys are available prior to beginning this procedure.
The part that needs replaced is the drive authorization module.
I have run across this several times before in the past with this module needing replaced.It is located under the dash and usually takes less then an hour for replacement.
Here is the procedure for its replacement:
Remove/Install 1 Remove Extended-Activity-Module (EAM) (2) 2 Loosen the retaining lugs (3) which hold the DAS control module (5) in the EAM CAUTION: Ensure that the retaining lugs do not break off. NOTE: Use radio removal tools (4) for removal. 3 Remove the DAS control module from the EAM NOTE: - Before installing a new DAS control module, determine in the old DAS control module whether keys are banned and code suitably in the new DAS control module. - The chassis number must be stated when ordering a new control module. 4 Install in the reverse order 5 Move ignition key into position 1 for at least 40 seconds. 6 Check whether the vehicle can be started with all keys.
The part has to be ordered from a Mercedes dealer with your vehicles VIN number as it is VIN specific.
If more help is needed, use the reply tab to continue our conversation. If no further assistance is needed, kindly rate my service.You can rate at any time and we can continue to work on your question as this will not close out your question.Keep in mind in some cases it can be difficult to fully diagnose or help repair your vehicle without seeing it and I work on delivering the best possible answer from what I see to work with.Thanks Pete.