Prizm (Differential)
WARNING: This page is about a different car, the 1989 Geo Tracker and 1989 Geo Prizm. However, it is still accessible from the selected car via links, so may be relevant.
Remove drain plug in bottom of differential cover and drain fluid. See Figure. Install and tighten drain plug. Remove fill plug on side of differential cover. Fill with ATF until fluid runs out of fill hole.