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Answered in 28 minutes by:
Technician: Colin Vincent
As you probably have an idea it is black toner related as in there is insufficient black toner going onto the drum and the density sensor throws a toner dispenser error as a result. It's not a low toner issue as you said they are new so it has to be a dispenser issue. The toner is taken from the dispenser to the drum via an auger drive which is driven by a motor. Either it is not turning through a fault or more likely it is clogged up with old hardened toner making it bind or preventing insufficient new toner flowing through. (often happens if toner has got damp in storage at some point and it hardens in lumps when it dries)
Because the toner is extremely nasty stuff to breath and servicing the dispenser is messy and requires a toner vac to remove the old toner safely (it has special filters), i strongly recommend you get someone to take a look at the dispenser for you.
Even a technician may not want to repair a fault in the dispenser itself if it is confirmed for the reasons above. They may want to replace the dispenser as a unit.