It is not necessary to regularly check rear axle fluid unless you suspect there is a leak or you hear an unusual noise. A fluid loss could indicate a problem. Have it inspected and repaired.

To get an accurate reading, the vehicle should be on a level surface.

If the level is below the bottom of the filler plug hole, located on the rear axle, you will need to add some lubricant. Add enough lubricant to raise the level to the bottom of the filler plug hole.

See Recommended Fluids and Lubricants to determine which kind of lubricant to use.