The 6.5L GMC Diesel engine operates differently than a typical internal combustion engine. When the engine is cold, the diesel fuel inside the fuel system can gel, making it difficult to start the engine. To fix this problem, the 6.5L engine uses a series of glow plugs to heat up the fuel, making it usable in the engine. When the glow plugs go out, you'll lose the ability to start your engine in cold weather.
Lift up the front of the truck using the jack and support it on the jack stands. Remove the driver's side wheel using the tire iron. Remove the plastic fender liner using the flathead screwdriver to remove the clips holding it in place.
Unplug one of the leads to one of the glow plugs using your hands. Remove the glow plug from the engine using the 3/8-inch ratchet and a deep-well socket. Discard the old plug.
Install the replacement glow plug into the engine in the reverse method of removal. Plug in the wiring to the glow plug.
Repeat Steps 2 and 3 for the remaining glow plugs.
Reinstall the fender liner using the factory clips, reinstall the wheel with the tire iron, then lower the truck off of the jack stands with the jack.
