P1666 iirc is a syncronization timing error,can be caused by faulty cam sensor on top of rocker cover. (if TDCI)

Ford modified them, and a good tip is to put a 12v ignition feed to the pin that is the 5v reference on the sensor, gives a better signal.

I think the modified sensor is grey and original is black, 90% sure on that. Long time since I fitted one.




sensor on eBay - http://www.ebay.co.uk/itm/ford-FOCUS...item1c15c538d5