2003 GMC Sonoma Owner's Manual - Page 316

Four-wheel Drive Lubricant checks in this section also apply to these vehicles. However, there are two additonal systems that need lubrication. How to Check Lubricant Transfer Case When to Check Lubricant Refer to the Maintenance Schedule to determine how often to check the lubricant. See Part C: Periodic Maintenance Inspections on page 6-30. To get and accurate reading, the vehicle should be on a level service. If the level is below the bottom of the filler plug hole, you'll need to add some lubricant. Remove the plug and add enough lubricant to raise the level to the bottom of the filler plug hole. Use care not to overtighten the plug. What tQ Use Refer to the Maintenance Schedule to determine what kind of lubricant to use. See Part D: Recommended Fluids and Lubricants on page 6-32. 5-53