I have a 99 volvo s80, non-turbo and occassionally when my car has been running for a while and I brake a message will pop up in my computer screen that says, no oil pressure stop safetly asap and then it disappears. What do I took it to get a diagnostic check and the printout stated nothing about the oil pressure. What should I get checked?

 

Your engine is filled with carbon from improper oil change frequency. Pull the pan, clean it out, reinstall along with pickup tube and o-rings.

 

bad oil sump/pan o-rings. I just had the same issue and did it on my car. Read the sticky above on Oil Sump O-rings replacement. Keep in mind, this is probably the hardest repair given the engine still on the car. the sub-frame has to be dropped way down. My advise is not to proceed without engine lift/hoist.