Suddenly, my remote key stopped working last night. Thought it was the battery, so changed it but still it doesn't work. Tried re-programming it and it beeps when buttons are pressed but still no joy once out of learning mode. The key still starts the car and unlocks it when done manually in the key hole. It's an OEM flip key, which I bought off ebay from a forum recommended seller. Any ideas? Also, when trying to get it into learn mode, the temp needle is now stuck and won't return to zero, and reads beyond the normal halfway running temp when the car is started so how can I fix this as well?

The temp gauge has fixed itself, so just the key.

I bought a chinese key fob thing to see if it would work with my Focus, turns out it works exactly once before the car believes that it is being stolen and stops the remote locking from working.

This is fixed by rebooting the GEM, which can be done via Forscan. Once you've reset the module verify that the original key works again, then try to get the car to learn the new key.

If that doesn't work then you're out of luck I'm afraid, and will probably have to try a different key/get one ordered from Ford/a specialist auto-locksmith.

The key has worked fine for several months, just decided to pack in on Sunday. It’s not a Chinese knock off, did your key still start the car when the remote locking stopped? If so I’ll get an ELM327 and Forscan and see what’s what.

It's likeky that the circuit board has died.
They're easy to swap out.

Sent from my SM-G965F (S9+)

What’s the procedure for swapping these, and where can I get one?

Tbh, flip key boards don't show up on ebay very often.
Probably best to source a new fob and swap the boards.
I would personally get the current fob tested first.
Most key cutting places keep fob testers that will pick up the signal if the board is transmitting.
I have a handset myself and I have sorted a few keys out in my time.

https://rover.ebay.com/rover/0/0/0?mpre=https%3A%2F%2Fwww.ebay.co.uk%2Fulk%2Fitm%2F191756451822

Sent from my SM-G965F (S9+)

happened on my old old fiesta. Water ingress slowly over the years, got into the sensor in the car above the rear view mirror. I just lived with it but apparently most of these systems are basically the same and a board swap like someone has mentioned can sort it out. However, my Mechanic was also wary of messing around with it as he didnt want to risk messing up the keys &  immobiliser. so it got left.

Contracted the seller and they said they didn’t think it could be the circuit board because the key is recognised when pressed when the car is in learn mode?

If the key was recognised then it would work properly.

Sent from my SM-G965F (S9+)

 I’m going to have it sent back to them for testing, because it recognises when I press a button on it in learning mode but then it still won’t lock/unlock the car when I use the buttons.

So apparently they've tested it and it works fine, I'm wondering if something in the cars packed up or it hasn't learnt it properly after swapping the batteries? What may have gone wrong and how do I test that this is the case?