I am pretty sure I am not a dumbass lol

I pressed the gas door and doesn't open. I even tried to press the switch under the driver door and nothing. Is there some sort of trick or release?

 

Is it a PHEV? https://www.mercedes-benz.ca/en/owne...asoline-engine
You said you pressed the button? Did the message pop up?

 

Yeah it is the E53... Yeah I pressed the button.

The dealer stated that on a full tank of gas, the door will not open. It needs to be under certain levels to have it open. This is super odd? I wonder why they did this?

No message pops up when pressed.

 

Very strange

 

What about the light? Is the light on the button flashing?

 

OP says gas cap hatch won't open when pressed. That is by design. Also says pressing switch in driver door storage pocket won't open the hatch. This switch must be pulled to release the fuel hatch door.

 

True, if OP viewed the link I provided, there is a video showing everything at the end. I just thought this can't be OP's first tank of gas on this vehicle right... Or maybe it is.

 

One time I had the situation of getting to the gas door, and it would not pop open, despite the key being in my pocket, and the car being unlocked.

I locked the car using my key, and unlocked it right away, and after that, the gas door opened like a charm when pressed.

 

That is possible but OP has a PHEV so it has to depressurize first.

 

I filled the gas tank on my E53 Hybrid today and then drove the five miles home in EL mode. I tried opening the fuel door flap with a full tank and had no issues. The depressurizing message popped up on the screen and the flap opened. I think your dealer just made up the "feature" about the flap not opening with a full tank.

 

How come theirs doesn't work though?

 

I am not convinced that the OP's fuel flap switch is not working. I suspect that he pulled the switch and the flap opened.

 

True, I never thought of that.

 

Possible explanation....

After the car was parked unlocked for several hours I approached it without the key fob, opened the door, pulled on the switch in the door pocket and the flap did not open. I returned with the key opened the flap, started the car, and closed/opened the flap several times.

A few minutes later I took the key back into the house (150 ft away) and returned to the car without the key. This time when I pulled the switch the flap opened. Not sure if this means the car has to be asleep for awhile before the switch is disabled.

 

I give up...

I tried opening the gas cap flap again today without the key. Unlike yesterday, the red light on the switch flashed, depressurizing noises could be heard, and the flapped open. It would be helpful to understand how the system actually works. I wonder if there is a manual way to depressurize the tank, and open the flap.

 

It says you might need to drive it for 1/3 miles? https://www.mbusa.com/en/owners/manu...asoline-engine