I have owned this E320 since new, and it always performs excellently, but suddenly a few days ago, it refused to crank. The K-40 unit and all the fuses were checked ok. The starter sounded to have engaged but did not crank. What can be done ? Will any one please advise!

not to ask the obvious, but, dead battery? did you try to jump it? sorry if that's too plebian...just a guess

Tks Cliff,

The battery is new and fully charged, but could not figure out what went wrong.

solenoid could be shot...

i had a problem with starting with my s-class check this forum to see if your problem is the same:
https://mercedesforum.com/m_72057/mpage_1/key_/tm.htm

The solenoid seems to be OK, because I can hear the engagement sound , but only the crank does not happen. I will follow the S-class solution to check it.

I suspect that the starter motor might have poor contact or worn-out brushes. I will try to take out the starter and check it.

Just had this issue on my brand new corvette.Everything worked but car would not crank. Checked the battery and the negative terminal was loose (from factory???) and had subsequently corroded. Cleaned off and re-installed, tightened and coated both terminals with di-electric grease.Everything now ok. Check your cables at the battery.

Latest update: The starter cable was not conducting properly, and not the other possibilities. After changing a new harness, the car is OK.