That is how it’s supposed to work. On the W166 they used a linear actuator (electromagnetic coils in the shock absorbers) to lift the hatch. This allows infinite adjustment of the opening height. This is designed so that you can set it up to not hit your garage door. When you are in the clear it is permissible to manually raise the hatch the rest of the way by gently pushing up on it.

Contrast this with the W164 system that uses a hydraulic pump. This one you cannot move the hatch yourself.

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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