BMW E46 320d 330d glow plug controller unit replacement

I have decided to replace my glow plug control unit after a long time ignoring this diagnostic error on E46. Replacement is straight forward with basic tool and it takes less than 30min. include reinforcement plate removal...



what's glow plugs preheating control unit does?
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It helps preheat glow plugs for certain amount of time so that the car can smoothly start and helps reduce smoke emissions and slightly improve MPG.
After engine starts preheating control unit continue powering glow plugs for 2-3min. to help with cold engine combustion process for a smooth run.


Symptoms of bad glow plugs preheating control unit
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Sometimes there are not any symptoms at all, everything works fine even at the cold weather until one day the car start smoking during the engine start, little rough idle but after while it runs smooth, then next time you start the car and for some reason the battery doesn't have enough power and its finished with difficulties to start the engine to no start at all.


why the glow plugs preheating control unit go bad:
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There a few different reasons for the damage of this control unit. On our E46's is mostly because of the fitted location, imagine control unit connected to the vibrating diesel engine block under the car 10-15" from the road surface at any weather or road conditions, Even that unit is sealed the circuit board inside control unit uses very thin wiring connections and it is covered in silicone filament inside the box, but after the years of the abuse of this control unit wiring loose connections inside the circuit board or get burned by short circuit during the vibration on already damaged connections. Second reason are impatient drivers which doesn't want to wait a few seconds till' the glow plug dashboard light goes away and start the engine anyway or keep restarting engine without waiting.