This Preliminary Information communication advises the technician about the calculation and operation of the engine oil life monitor. The monitor calculates the percent of oil life remaining, based on 3 pathways. The first pathway for oil life calculation is engine revolutions. The second pathway for oil life calculation is the mileage form the last rest for all General Motors powertrains except the Volt. The third pathway for oil life calculation is the amount of time the oil is in the engine. The Volt uses a 2 year timer instead of 1 year. It also uses the engine revolution counter. It does not use the mileage pathway to count down.