Ranger said:
Are you talking about the check oil level message, the change oil message or the oil pressure light? If you are talking about the check oil level message, and the oil level is still on the stick, then I would suspect a faulty level sensor.
The level sensor is a simple float switch. I just replaced mine. The float came off the end of the sending unit on my old one. It was just a small clip that held it in place, and the clip apparently broke and is sitting in the oil pan along with the float. On the new ones, the end is molded plastic that probably has a little better structural integrity than the stupid clip-on thing did. Despite what our old buddy Rob said, I wouldn't replace the sensor with oil in the sump. It sits low enough that you'd have quite a spill unless you have the car at an extreme angle and/or only a few quarts in the pan.
The oil pressure light uses a completely different sensor that's above the oil filter adapter. The oil pressure is normally pretty low at idle, but if it's low enough to trigger the light to come on, the sensor could be bad, the harmonic balancer bolt could be loose, or the oil pump could be marginal. I only remember hearing about one instance of a bad oil pump, so that's a pretty unlikely solution. Rob used to recommend using one of the HDD oils like Delo, Delvac, or Rotella 15W-40 oil to alleviate intermittent oil pressure light issues after the sensor had been replaced with an OEM (AC-Delco) sensor.