If its switching off eventually presumably whatever it is still works. Try resetting the electronics by disconnecting the battery for a few minutes.

Petrol or diesel?any engine warning lights on?You will need a diagnostic check done to get an idea what is going on.

This is a known issue, more common on the 307 than other models, that is rectified by removing the front grille and cleaning the fan relay conenctions that sit there, quite exposed to the elements.

I'm no electrical genius but I wonder if the signal is getting to the relay to activate the fan, but isn't receiving the signal to shut it off?

I've cleaned the connections and mounting point on the relays with electrical contact cleaner on a few 307s and the problem didn't return.

It might not work on your 3008, but as its a simple thing you can try at home for free, worth a go.

Edit: Just read the bit about sparks. You could have damaged your BSI.

Edited by Gibbo_Wirral on 23/01/2015 at 12:54

Leaving the oil cap off plays havoc with the engine crankcase breather/oil system.For some reason when this happens,the engine control unit puts the cooling system into default mode and runs the fan.A good diagnostic scanner would have flagged the code dtcP11aa.A faulty breather valve in the cam box cover will cause the same issue and bring on the fan.