2006 Pontiac Montana SV6 Owner's Manual - Page 351

Carrier Assembly-Differential (Rear Drive Module) When to Check and Change Lubricant Refer to the Maintenance Schedule to determine how often to check the lubricant and when to change it. See Scheduled Maintenance on page 6-4. If the level is below the bottom of the filler plug hole, located on the differential, you will need to add some lubricant. Add enough lubricant to raise the level to the bottom of the filler plug hole. A fluid loss could indicate a problem; check and have it repaired, if needed. What to Use Refer to the Maintenance Schedule to determine what kind of lubricant to use. See Recommended Fluids and Lubricants on page 6-11. How to Check Lubricant To get an accurate reading, the vehicle should be on a level surface. 5-47