Replace the failed Glow Plugs in your 2007.5-2010 Chevy/GMC 6.6L LMM Duramax. Commons symptoms of a bad glow plug can include a check engine light, hard starting, misfire/rough idling, loss of power, white or black smoke, or a decrease in fuel economy. A glow plug is a heating element that heats incoming fuel and air to encourage efficient fuel combustion in a diesel engine. This heat can be necessary for a diesel engine to start, run, and function optimally especially in colder weather conditions. Each cylinder of your engine typically has one glow plug, either in the pre-chamber or in the combustion chamber. When a glow plug fails to work properly, the combustion chamber doesn't have the necessary heat that can be required to help ignite the fuel. Depending on the outside temperature, it may take several attempts at starting the vehicle before achieving ignition. In freezing winter temperatures, it is possible for a diesel engine to not start at all without operational glow plugs. Shop glow plugs, harnesses, and controller/control modules from all the leading manufacturers such as Diesel RX, Dorman, Bostech, Ford/Motorcraft, Dtech, Alliant Power, GM/AC Delco, and Diamond Advantage By Navistar.