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this is a fault with the glow plug control module to pcm communication.
the glow plugs are usually switched on/off by a glow plug control module wich can be controlled by the main diesel engine control unit or the powertrain control module (pcm)
the glow plug control module will receive a control signal from the diesel control unit/pcm then the control module will then switch/regulate the power supply to the glow plugs.
there is a good chance that there is a wiring issue between the glow plug module and the pcm this is the most common issue with these .