Low engine oil light

We just bought a used 2003 Chevy venture. It has 14K miles on it so it's still under factory warrenty. After we got it home we noticed that after it gets warmed up and you shut it off and leave it off for about 30-40 minutes and then restart it that the low engine oil light comes on for about 10-15 secs, before going off. This is the only time that the light ever comes on. I called the dealer and asked them about it and I even took it in and they looked at it and couldn't find anything wrong. They also went ahead and change the oil and it's still doing it. Does anyone else have this problem? Is this just normal because the vehicle thinks that there should be more oil on the engine because the engine is still warm? Like I said it only does this after the car is warmed up and then when we let it sit for around 30-40 minutes. It won't do this on cold starts or on restarts.

Thanks for the help.

These sensors are merely switches, which switch states when oil is up or low. The easiest way to chek it would be to check the resistance when the oil is correct, then check it when the oil is low, (drain enough to expose the switch sensors). If this works, the problem is likely one of software on the ECM or BCM. These vehicles have had their share of software issues. You might ask the dealer to reboot the ECM or BCM, whichever is responsible for the light. Ray