Just purchased a 1995 STS, first thing I noticed is that the display says check oil? I checked the dip stick and it says almost full. Is the sensor off? or does it do this when the oil isn't completly full?????
It's most likely the oil level sensor. The Northstar engine has a DEEP oil sump, and holds 7 quarts of oil. If working properly, the oil sensor won't report a low oil level until the sump is down to about 5 quarts or less. If the sump is full (indicated by the dipstick), but the system still says to check oil, it means the sensor is bad, or the wiring to the sensor is damaged, or the connection at the sensor isn't good, etc. The sensor itself is relatively easy to replace -- it's on the front of the oil pan, pointing forward.