The code P0675 tells you that something in the glow plug circuit is faulty causing the glow plug on cylinder #5 to fail to heat up. The entire circuit must be checked to locate the fault. Note: If a P0670 trouble code is present along with this DTC, carry out P0670 diagnosis before diagnosing this code. Nov 2, 2011. #3. The glow plug light is driven by the ECU, and it should come on every time you turn the key on. It will only stay on for 1 or 2 seconds unless it is cold enough to require pre glow for starting. The light is not actually part of the glow plug circuit, so fuses and relay are not the cause. Mrchntmarine. so i haven't picked up the car yet, but the advisor says the glow plug light staying lit was caused by fuel flow issue with the diesel fuel filter. they went ahead and did 35k service early because of that. they are suppose to have saved the diagnostic's for me. think i was about 33k miles. 5NiBUc.