At -12 a diesel isn't going to fire up like a gas car. Heck a gas car isn't going to be happy!

Replace the glow plugs, and send the injectors off to be tested if you think you have a problem.

Or just plug it in.

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2006 CL500
1969 280SE
2023 Ram 1500
2026 Genesis GV70
2007 Tiara 3200