The procedure is to install the drain plug to the
Differential, clean any dirt from around the differential fill plug, remove the fill plug from the differential, fill the differential with 75W90 synthetic axle lubricant, GM P/N 12378261 (Canadian P/N 10953455) or equivalent, inspect the gear lubricant level to ensure it is even with the bottom of the fill plug hole to no lower than 6 mm (0.25 in) below the opening, install the fill plug to the differential, lower the vehicle.