Oil pressure sensor

I am goin to lift a mates a4 soon as I can pick it up cheap, the problem with it is that the oil light comes on when you rev it over 1500rpm. He says it needs a new oil pump but from what he described I think it could be just the top oil pressure sensor! It has been lyin up for a couple of months so I'm goin to unplug the fuel pump and tick it I've a couple of times and take the rocker cover off to see if the oil pump is still working. Am I right in doin this to see if it's the pump or the sensor? I also have a spare a4 sittin there so can take any parts I need out of it just need to figure out if it's the pump or the sensor. Any help would be greatly appreciated.

There both 1.9 tdis, ones a 90bhp ahu and the other is the 110bhp afn.

Thanks Jason.