Checking Fluid Level: Differential
WARNING: This page does not describe the selected car, but rather 7 other vehicles, including the 1991 Toyota Tercel, 1991 Toyota Supra, 1991 Toyota MR2, 1991 Toyota Cressida, and 1991 Toyota Corolla. However, it is still accessible from the selected car via links, so may be relevant.
Remove filler plug. Fluid should be level with bottom edge of filler plug hole. If fluid is level with opening, install fill plug. If fluid is low, fill until fluid is level with fill plug opening.