The GM Oil Life System is not a mileage counter. It is actually a
computer-based software algorythm that determines when to change oil based on
engine operating conditions. There is no actual oil condition sensor. Rather,
the computer continuously monitors engine-operating conditions to determine when
to change oil. Over the years, millions of test miles have been accumulated to
calibrate the system for a variety of vehicles. The system was first introduced
in 1988 and is now on more than 10 million GM vehicles.
