Ford focus passive key not detected
I own a 2006 Ford Focus sport (56 plate).
It has a keyless entry / ignition system.
The other day, I approached my car as normal, and the car would not unlock despite being in close proximity. I was required to use the unlock button on the fob to gain entry which is unusual. I then sat in the drivers seat and tried to turn the keyless ignition stalk however the stalk would not turn and there was a message on the dash board 'PASSIVE KEY NOT DETECTED'. I then had to remove the key from the fob and use the ignition manually.
I considered that the particular key may have a low battery, or a broken battery so tried my spare which is rarely used- however it did not work.
I then tried to reprogram the keys to no avail.
The ignition system was replaced a year ago, due to a battery drain which was wrongly diagnosed by a ford dealership at around £500!
I was considering replacing the batteries in both keys, however it seemed strange how they both don't work.. So it would seem to be a sensor on the car perhaps?!
Any advice would be greatly received as I am looking to sell this car soon- other than that it is a perfect car.