Oil Light is on

So my mom has a 2001 Expedition with 4.6L and in the winter time the oil light comes on and the gauge drops below the "L" and it just stays there. It's not low on oil, where do I start?

 

hook up a mechanical gauge to see what the oil pressure actually is. you can't trust the cluster gauges.

 

if the oil pressure checks out ok, then replace oil pressure sensor.

 

alright thanks.

 

Is the truck making any noises??

 

No sir. It does not do it in the summer, it's only the winter. It did it last winter, and now this winter.