Way back in the dark ages of automotive diagnostics, in 1987, the ECU did have rudimentary blink diagnostics. You will need a blink code reader (basically an LED, resistor, and pushbutton in a pill bottle with 3 banana plug leads).

You need procedure 07.1-1120 to diagnose the system. The MB factory tool has a fancy counter that produces a numeric readout but it is possible to watch the LED and count the flashes.

__________________
The OM 642/722.9 powered family
Still going strong
2014 ML350 Bluetec (wife's DD)
2013 E350 Bluetec (my DD)

both my kids cars went to junkyard in 2023
2008 ML320 CDI (Older son’s DD) fatal transmission failure, water soaked/fried rear SAM, numerous other issues, just too far gone to save (165k miles)
2008 E320 Bluetec (Younger son's DD) injector failed open and diluted oil with diesel, spun main bearings (240k miles)

1998 E300DT sold to TimFreeh
1987 300TD sold to vstech