Barnyzuki

This might seem a silly question but seeing as my pump is missing completely I thought I`d ask. Does the pump run constantly when the engine is running, or as the name tends to suggest, does it only operate once the engine is shut down ?

My 52 plate 115TDi had the exact same fault when I bought it, I was even told by the seller it was the N/S driveshaft/CV joints. One new unit later and no wobble ! The whole replacement driveshaft with new CVs was around £70.