Amber oil light issue

I have a 2002 325i w/75000 miles. the amber oil light comes on after 30
seconds and remains on for 15 seconds every time I start the car. This
happens whether the car is cold, warm or whatever. The oil is full and it
indicates that the next service isn;t due for another 9500 miles. My first
inclination is the sensor, but the regularity and indifference to engine
temp might suggest a different issue. What can cause this?

Thanks in advance