2004 ML350 - My fuel door won't unlock. I've located the actuator, behind the trim on the driver's side (some ML350s have the door on the passenger side), and it has a lightweight metal tag on top that I assume is the manual actuator. I tried it once and it did seem to unlock the door, but since then I haven't been able to get it to work. I've turn, lifted and pushed down on the tab but nothing seems to work. I'm afraid to use too much force, and its difficult - I can barely get my hand in there. Once since I have had this problem, the door unlocked with the remote, so I don't think it is a fuse. But if it is, where is the specific fuse for the fuel door located? Approximate Kms on the car 170,000.
Am I right about the actuator, and which way should it be moved to release the door?

 

Page 263 in Owner's Manual.

 

Thank you, Maj. Dundee, for the reference to the owner's manual - I must have missed it previously. It worked as per the manual, but the part that is unsaid in the manual is to keep rotating the key/shaft until the pin is withdrawn from the door. Knowing what direction to moved the key (clockwise), was the essential information that gave me the courage to proceed. The key was very stiff at first but then turned easily. With the door open, I can now get fuel. I'll look for the reason why the actuator failed after re-fueling. Possibly a fuse blown. Thanks again.

 

For the sake of people in future who may have a similar problem, here is a photo of the manual release tab on the fuel door actuator. It seems quite lightweight, and as such I was reluctant to use much pressure until I knew what movement (clockwise) was required.