Brace the vehicle by engaging the parking brake and placing chocks around the front and back of at least one wheel. This ensures the vehicle will not roll while you are underneath the rear axle accessing the differential. If necessary to allow additional access, jack the vehicle and then brace it with jack stands. To ensure the differential and vehicle remain level for optimal fluid level checking, use ramps on a flat surface, or park the vehicle with the rear on a downward slope, then jack the front upward until level.
Locate the rear differential. On the Toyota Tacoma, it is found near the center of the rear axle. The differential has a drain bolt at the bottom and a gear oil fill/check bolt toward the top facing the front of the vehicle.
Place a drain pan beneath the differential to capture any oil that may spill from the gear oil fill/check bolt. Loosen and remove the gear oil fill/check bolt.
When the differential is full, gear oil will dribble out of the gear oil fill/check hole. If no oil is drips out, the oil level is too low. If necessary, add the correct gear oil in the fill/check hole until the fluid begins to dribble out.