Common rail engines 648, 642, 651, have a ‘limp mode’ that it enters for faults where full power may cause more damage, but allowing limited operation to get to a workshop is allowable.

It effectively turns the car into a 240D when it happens.

The modern fuel systems don’t seem to be as prone to losing prime as the mechanical engines were. These have a pusher pump in the fuel tank to feed the filter and high pressure pump at the engine.

If you get an iCarSoft or a factory scanner on it there should be stored codes in the power train computer to lend a clue what happened.

Exhaust filter clogging is a possibility but you can read ash load and percent obstruction with the scanner.

__________________
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