I think that I've found the cause:

"The permanent fualt memory in the diagnostic module has been eliminated and replaced by a fault memory. As a result, faults in the fault memory are erased if the voltage suply is interrupted.

In addition, after the fault memory is erased or after connecting the battery, the pulse display "1" (no fault) does not appear any longer.

The pulse readout "1" is not output again until the diagnostic module has checked all the components and control chains during the subsequent journey and has not found any fault."

Just one question - how many "journeys" does it take for the diagnostic module to check all the systems/control chains?

EDIT: A "journey" has been accomplished if:
- road speed > 4 km/h
- engine speed > 700/min
- engine switch off for 30 seconds

Still don't know how many journeys are required.

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Daily Driver: 02 E430 4MATIC
In the family: '03 E500 // '04 ML500 // 64 220SE