Volvo Repair: S60 Low Oil Pressure, oil pressure sending unit, low oil pressure

Question
I recently purchased a 2002 volvo s60 with 68 thousand miles on it, the carfax was clean as far as i could see albeit electrical work and from what ive read about faulty electrical systems in the new volvos, that may be a blessing.  Anyways, as i was driving home from the dealer a "low oil pressure stop car safely" message appeared, which then changed to "no oil pressure stop car safely" I have turned it on 3 times since then, not driving it... and each time it has said "No oil pressure stop engine"  I havent driven it at all for fear of tearing the engine apart and i would like to know what the problem is.  When i test drove it days before there were no lights, i was told the dealership technicians then did an oil change before i drove it off of the lot.  Could it be the oil pressure sending unit, or the oil pan o rings?  Any information that i could take with me to the dealership would be excellent.

Answer
It is one of 2 items.  The O-rings for the oil pan pickup are known to go bad on that car.  It happens enough that they made a service bulletin for it.  That is almost certainly your cause UNLESS your engine is sludged.  Take off the oil fill cap and look at the bottom of the cap.  If it has black or dark brown crusty deposits you have an oil sludge problem and most would then most likely have internal blockages of oil passages.  That would be cause by the previous owner not doing his oil changes frequently enough.  This could be verified by dropping the oil pan and taking a look what buildup there may be.  If you take it to the dealer let them go ahead as if they were going to do the oil pan seals BUT if they find sludge you are most likely going to need a new engine.  Any time I have tried to do an oil flush it usually makes things worse.  Obstructions that were not blocking any major passages get dislodged and then get stuck in a more important channel.  One of the other technicians in my shop seized a motor doing this just yesterday.  I think that this worse problem is more likely in your case because the problem arose right after an oil change but I cannot be certain, get them to check it out.

James