Could be the following... Low oil pressure = Lack of oil, lack of oil quality, oil filter blocked, lazy oil pump, faulty sensor = fix is an oil and filter change followed by oil pressure check ( garage job ) if this makes no difference . A garage will then say its the pump or sensor although it may be in your interest to change the sensor anyway as they are cheap plus you get to check the wiring's good while at it --- high oil pressure could also account for an oil light depending on if your van is set up to monitor this. An increase in oil is normally over fueling with fuel passing past the rings, most times its noticed by blowing a gasket or it running like a pile of crap as the crank struggles