GM Service Manual Online
For 1990-2009 cars only

The PCM controlled lamps are intended to alert the driver to an operating condition which may require immediate attention.

The PCM commands the Low Oil Level Lamp ON if the engine oil level sensor indicates that a low oil level condition exists. The PCM determines whether or not to test for low oil level based on the difference between engine coolant temperature at the last shutdown and engine coolant temperature at startup. This is to ensure that the oil has drained back into the oil pan before testing.