I have a June 2018 build model 3. The other night I was plugging in the charger in the dark and accidentally tapped the charge port door with plug. Not hard mind you. A moderate tap. I heard something fall to the ground so out came my phone flashlight. I found a diamond-shaped piece of black plastic (see photo). I took it inside for the night.
Next morning I removed the charger and the door closed. All seemed normal, but I could hear the door servo motor trying/straining to close the door further over and over. Motor noise....motor noise... In daylight I took a look at the backside of the door and found the diamond-shaped recess that fit the missing piece. I went inside and got some DAP super glue, applied a few dots, and clamped it back in place with a bag clip until dry. I don't know what glue they are using at the factory, but it was definitely not sufficient in this case. I retested the door with the piece/sensor back in place and no more motor straining. It must be a magnetic pickup sensor to detect fully closed position.
Anyway, if you are getting odd behavior from your charge port door, check for a missing sensor piece. If it's missing, there will be a recess. If the sensor is there, it will sit flush with the surrounding plastic on the back of the door.
Next morning I removed the charger and the door closed. All seemed normal, but I could hear the door servo motor trying/straining to close the door further over and over. Motor noise....motor noise... In daylight I took a look at the backside of the door and found the diamond-shaped recess that fit the missing piece. I went inside and got some DAP super glue, applied a few dots, and clamped it back in place with a bag clip until dry. I don't know what glue they are using at the factory, but it was definitely not sufficient in this case. I retested the door with the piece/sensor back in place and no more motor straining. It must be a magnetic pickup sensor to detect fully closed position.
Anyway, if you are getting odd behavior from your charge port door, check for a missing sensor piece. If it's missing, there will be a recess. If the sensor is there, it will sit flush with the surrounding plastic on the back of the door.