I lost my last set of car keys a few days, and as I didn't want to pay the rather extortionate amount of money that an official dealership wanted to charge to replace all the locks and immobiliser system, I went to an unofficial locksmith, who cut me a correct key but was unable to program the transponder in the key correctly. A day later I actually found my original key, however when I attempted to start the car with it it came up with the immobliser malfunction message. I've seen some places recommend unplugging the battery for 10/15 minutes to reset the electronics system, however don't know if this will work and also don't know if this will stop my original key from working, just looking for any advice/technical info on what might happen if i disconnected the battery or if I did anything else with the car. 

On 10/12/2016 at 5:28 PM, bbsblackwood said:

I lost my last set of car keys a few days, and as I didn't want to pay the rather extortionate amount of money that an official dealership wanted to charge to replace all the locks and immobiliser system, I went to an unofficial locksmith, who cut me a correct key but was unable to program the transponder in the key correctly.

If I am reading this right, no key (new or original) will now start the car.

Disconnecting the battery should not affect the PATS (immobiliser) system. It should not forget old keys, nor magically accept new ones. It would be useless if that happened regularly.

If the locksmith visited the car, and tried to programme its PATS system, it is possible that he erased all the keys (This has to be done if a key has to be deleted from its memory), but could not then add any. Hence the failure to recognise the original key. Unfortunately, the only way out of this would be the Ford garage or Ford specialist auto-locksmith.

Programming new keys to PATS is intended to be done in the car, not in the key.

The PATS lamp should flash out a code after a minute or so of rapid flashing or steady on. Try Googling PATS flash codes. This would confirm if the system was working, but just did not recognise your keys, or if there was some other failure.

A freely downloadable programme called Forscan can re-programme PATS in many Fords, but the latest year for the FIesta seems to be 2011 (Focus is similar). So it looks like access to the full (official) Ford system will be needed for this 2013 car. I am sorry if this seems bad news, but it is all I can offer.