2008 GMC Yukon Owner's Manual - Page 424

What to Use Refer to the Maintenance Schedule to determine what kind of lubricant to use. See Recommended Fluids and Lubricants on page 6-13. Headlamp Aiming The vehicle has a visual optical headlamp aiming system. The aim of the headlamps have been preset at the factory and should need no further adjustment. However, if the vehicle is damaged in a crash, the aim of the headlamps may be affected and adjustment may be necessary. 2500 Series A: Fill Plug B: Drain Plug If the level is below the bottom of the filler plug hole, located on the front axle, you may need to add some lubricant: If oncoming vehicles flash their high beams at you, this may mean the vertical aim of your headlamps needs to be adjusted. It is recommended that the vehicle is taken to your dealer/retailer for service if the headlamps need to be adjusted. It is possible however, to re-aim the headlamps as described. • When the differential is cold, add enough lubricant to raise the level from 0 (0 mm) to 1/8 inch (3.2 mm) below the filler plug hole. • When the differential is at operating temperature (warm), add enough lubricant to raise the level to the bottom of the filler plug hole. 5-56