Diesels do not use spark plugs (like gasoline engines) as diesels rely purely on compression to ignite fuel. The more compressed the gas is, the hotter it is and the hotter the engine, the easier it is for diesel to ignite.Glow plugs are used to provide heat for the diesel engine and are powered by the battery. When it's very warm outside, their role isn't very important but when the temperature is cold, they are vital.
Replace the glow plugs.
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