Assuming you have a key type fob.
I had a similar problem with my Scenic key, it turned out to be the ultrasonic LED in the key had become detaced from the small circuit board inside the key, a quick dab of solder sorted this, it has gone like this twice in 3 years.
The Bit you are looking for looks like a small 5mm black bulb and usually sticks out of the front of the key on two pins, this is fairly fragile and flexing when pressing the key causes a dry jont where it solders to the board, look (very closely) for micro cracks in the solder and prod the pins see if one is loose.
I could get mine to work with the key still together by pushing the LED back gently so it made a contact, which is useful to get you home.
Also check the solder joints to the switch, this also applies to the card type keys, i have repaired dry joints on the switches on these.
hope this helps.
The key is not the problem, I've checked it and it's working fine.