Focus MK2 2.0tdci weird problem

Hi lads,

I'd need a bit of help to figure out what's wrong with this car.
2009 Ford Focus 2.0tdci Automatic transmission.
Car starts fine but exactly after 30seconds main relay under the bonnet clicks for a split second and engine cuts out. 
I can restart the car no problem but after 30s it dies again.
Same story with ignition on but engine off. I can hear relay clicking every 30s.

I've checked fuses and relays. All seems to be ok. The owner replaced instrument cluster in another garage but it didn't sort out the problem.
I've only one fault in PCM P1622 Immo ID does not match (only comes up after relay clicks).

Any ideas? 

Thanks in advance