What is this component

MELF diode. Easy to test with a multimeter.

Not doubting your knowledge but someone told me on a rover forum that they replaced theirs with a 10nF capacitor

S5Y is a type of diode. Believe who you want to believe. If you don't like my answer, you're free to ignore it COMPLETELY. IDGAD

According to this datasheet, the S5Y is a 2000 Volt, 5 Amp rectifier diode. I can't imagine why such a part would be found in a key fob.

But I'm skeptical about it being a capacitor too. It just doesn't look like one, but that may be just the picture.

Please post a picture of the part viewed from the side at ~ a 45 degree angle. Also include in the picture a ruler or some object so we can get an idea of it's size. Post another picture of the board with the location of the part marked. Make sure that all pictures are in focus.

H I really appreciate the input off you all. I have discovered what the component is for definite. I searched with duckduckgo instead of Google and found this on a rover site. My car is a land rover discovery 1996.

"The 3TXA and 3TXB fobs use a canister type crystal for the clock signal, ideally this should be glued to the circuit board but it is only held in place by it's two wire leads. It's common for the wire to fracture where it has been soldered to the board"
Mine had snapped completely at the base off the component.
The component in question is the size of a large grain of rice.
I ordered one for tomorrow but I had a look through my collection of broken stuff and found one in a car radio. It didn't have any numbers but I chanced it and my landy is running again.
My immobiliser circuit board was badly water damaged when I got it but managed at the time to bypass traces and replace few resistors
And it worked for 2 years then died. I thought it was worth a last try with it so I swapped all the chips and transponders over. And the alarm and central locking worked but not the immobiliser. My son was swapping a battery in the key and snapped that component off the fob board.

Glad to see that you consulted multiple sources to resolve the problem. The reason the picture rang a bell was because in the early days of SMT (Surface Mount Technology) manufacturing (ca. 1998) we had to use a "MELF" diode and it was certainly an enormous PITA.