My MIL came on for the same reason. I opened the hood and reached in and worked the EGR diaphragm up and down a few times. After 25 starts the light will go out. If every time you check your oil you do this, the light will stay off.
I suspect the vacuum actuated valve is the culprit. These are known Toyota problems, and are relatively easy to correct. I'm wating for some warm weather.
Musi