Tailgate issues - check your battery - I suspect the pump times out if you have low voltage and it can't build enough pressure.

With all doors closed put the key in I position (just the radio on)
Press the R button 3 times in the center of the cluster
The LCD should show you the battery voltage
Glow and crank the engine and see what the voltage drops to.

Mine was going down to 9 volts on glowing and 6 volts on cranking
W164 battery replacement

Once I replaced the battery last February I have not had any issues with the tailgate since. Even when parked with the rear end up on my sloping driveway. Not sure if it was the better voltage or cycling power that did the trick but it definitely did for me.

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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