Ok..let'* step back a moment.
When you first turn it on??? When you turn on the key or when you start the car?
When you turn on the car...most lights will come on automatically for a moment during the self test of the light.
On the sensor..it'* about $40 and probably not the cause. They are very simple sensors and very reliable. Check the connection at the oil pan, oil leaks or things like that could cause a possible bad connection. Also to keep in mind is that the oil level sensor, MAF and Lean Bank One codes are common signs of corroded or bad battery cables.
In this case..first thing I'd check is the battery cables, remove each one at each end, clean...apply a light amount of dielectric grease and reconnect. As well...when the cables are off the battery, look under the rubber end booties for corrosion as well.