My focus tdci 1800 ran fine until recently. I was driving normally on a light throttle & the engine suddenly cut out. On cranking, I noticed the glow plug light flashing, but no start. After a wait of about 5 minutes, the engine started & ran OK, for about a week. Just the other day, the same happened twice. The first time the engine was hot & had been switched off for about an hour. the engine would not start. Again after waiting about 5 minutes, the engine started OK. Later on the same day the engine stopped while driving. After a few minutes, I heard the central locking operate (not by me), & the engine started OK. I have done about 120 mile since, & all OK Your answer would be most welcome Regards Clive Purdom

There are a number of faults I'm aware of with the focus which can cause driveability,cutting out and non start problems.
1 poor earth connections in engine bay, you need to check and clean ALL earth connections in engine bay

2 engine wiring shorts out against EGR valve (but this normally blows fuse F9 (20amp) wiring needs to be repaired and re-routed and secured

3 erratic running and non start (glow plug warning lamp flashes when this fault is present) this is caused by low fuel rail pressure and is expensive to put right you need to check for the following fault codes P0109, P0191, P0251, P1211, P2288, P2291
if one or more of these fault codes are present remove fuel filter and drain contents, inspect for deposits(black with silver particles) if deposits are 11mm you need to remove fuel tank and flush it out.
the following will need to be renewed:
fuel rail, high pressure fuel lines, fuel supply line filter to high pressure pump, fuel return line from high pressure pump to filter, kit protection blanking plugs, kit, leak off pipes, fuel injector clamp bolts, fuel filter, high pressure pump gasket,high pressure pump seal,high pressure fuel pump and timing belt.
I recomed you carry out you diagnosis in this order

Regards
Jim

This is one of them faults thats very difficult to diagnose but if what you say is right then i would change the drivers door lock ,they are repairable as they are a sealed unit on these cars,but i did have a similar problem with a petrol version on one of the first models of these cars about a 99 or 2000 as i remember and it would play up just like this ,open and close the door lock with key three times and it started.then be ok for a week then not start again so i had the key man down with his programmer and he checked it out for the key remote and found nothing wrong with either the master or the spare key and he said try changing the door lock because he had this problem before with other ford focus models and mondeos .Change the lock and it was ok for a week but the owner sold the car for a new car on the scrappage scheme so i never did find out it was ok after that