Pats - Focus 2006 - Fault After Starting Ok - Code 1,3

[ahodgett]

My Focus 2L TDCI Oct 2006 seems to have a strange PATS problem!

Red light goes every two seconds as expected. turn ignition to 2nd position, red light goes steady for about 3 seconds and then goes out, so far so good. However on starting the car, it starts ok, the red light sometimes comes on steady for a second or two and then flashes rapidly for about a minute and then gives the 1,3 code. Usually this happens when cold. Usually after about a mile or so light disappears and all is ok. Any ideas as to what's going on, as I understand it 1,3 means RFID in key not being recognised. Anyone else had this fault? Does the PATS play any part once the engine has started? Could it be the battery beginning to fail just a little, it's nearly 7 years old?

Regards

Arthur Hodgett