Suspected this wasn't working as the car has just had the engine rebuilt so it's been sitting for a while, anyway i took this off and connected a battery to it to get a circuit but it doesn't move, how can i free it off????
tried cleaning it up and some wd40 but no joy so far, and also to clarify, when it is activated when the engine is cold what should i see it doing????

 

ultrasonically clean it

if that fails buy a new (or S/H) one

 

Cheers, not to worry, seems to be working now
Will put it back on the car and test it again.