The transfer case on a 2003 GMC Yukon transfers torque energy from the transmission to the front axle when the Yukon is in four-wheel drive. Like the engine, transmission and differentials, the transfer case relies on lubrication fluid to decrease wear on the internal moving parts. The lubricant can break down over time, so you should replace it regularly. General Motors recommends replacing the fluid every 50,000 miles to ensure a long life and lasting operation.
Place the drain pan underneath the 2003 GMC Yukon's transfer case and remove the transfer case fill plug and drain plug with the socket wrench. Allow it to drain as much as possible and then reinstall the drain plug.
Insert the hose from the fluid suction gun into the transfer case fill hole and use the gun to draw out any remaining fluid. Squirt the fluid from the gun into the drain pan. Repeat until the transfer case is empty. You can purchase a fluid suction gun from your local auto parts store. They look similar to caulking guns and work by manipulating a plunger back and forth to draw the fluid in and eject it back out.
Pour the transfer case fluid into the transfer case through the fill hole. Fill the case until the fluid level rises to the bottom of the fill hole opening. Depending on the engine configuration and style of four wheel drive system in your 2003 GMC Yukon, your transfer case either uses Dexron III fluid or Autotrak II fluid. See your Yukon’s specific owner’s manual or consult with your local GMC dealer for exact fluid specifications.
Thread the fill plug in by hand and tighten it down with the socket wrench. Wipe any spilled fluid off the case exterior with the rag.
