Previa Oil Warning Light
To Dan in Winnipeg
I don't have a Previa, but it's predecessor the Van Wagon. The oil pan in my van has a sensor on the side. You can look at yours to verify. When I changed my pan gasket I found the sensor inside and it is a floater. Most of the floating material was missing and I suspect as happens to mine that when it warms up the viscosity of the oil thins and can no longer support the floating sensor which sinks and the oil light comes on. My sister had a similar problem, had the mechanic hook up the pressure gage to her oil pump outlet and the pressure was good. There are two sensors that feed the computer that signals the light in the instrument cluster. There is the level, which I just described and the pressure sensor.
The first time mine came on I got that sinking feeling that one expects to get when the engine is done. It took time for me to feel ok about the light coming on. If you feel uncomfortable, you could always get a pressure gage that you mounted as an accessory or if it is that floater in your oil pan, you could order the part new or find one at the salvage yard. That is my plan, salvage yard since my van is 1985 and still going strong.