The most probable cause is the battery is exhausted.
Yes, they have two batteries... Model CR2025 3v batteries have been changed but still not working
check the battery in the car and the batteries for the fob key
how to reset remote key fob for Mercedes SL 320
On the C280, the trunk is electro-mechanical. It should open either with the key fob, or with the "valet" key that slides out of the fob. The C-Class Mercedes' still have the traditional exterior keyhole. Also, on the C-Class, there is a switch on the center console between the seats that opens the trunk.
No
C200 key fob problem
Weak battery in fob?
Put the key in the ignition and turn the key 2 clicks to the On position and press and release the lock button on the fob. Then press and hold the unlock button on the fob 5 times and then release. This will reset the fob for your Mercedes.
To replace the battery on a Mercedes ml 350 key fob it is probably best to ask the supplier where it is purchased or there may be some instructions online.
I have a Toyota, and my key fob light stayed on also. I called the dealer, and they said the button on the fob was stuck down INSIDE the fob. So, I simply unscrewed the screw on the back of the fob, opened the fob, then put it back together. The fob was fixed. I didn't have to fix anything in the fob.
get a new one :I lol
$250 @ MB according to forum