Brother intellifax 4100 e display says to replace toner but cartridge is not empty. Is there a reset for the toner?

Brother Intellifax 4100e How To Drum and Toner

Open the front of the machine. Lift and pull the whole unit (drum) out. Once you have it out it's pretty simple to remove the old toner from the drum and install the new one.

Please do not be offended by any of the suggestions. I do not assume anything.
Toner can become "caked" slightly hardened, so if you have the opportunity to shake the toner inside its container, do so.
If you have replaced an entire unit, confirm protective strip has been removed from toner before installing into cartride or its proper placement.
These two suggestions are preliminary to comprehensive troubleshooting.
Try that

Open the door where the toner cartridge is, and push the clear key and look at the display where it will say reset no press 1 yes press 2. That should do it.

iy could be that the sensor or board is mal-function

There's no manual for "machine error 7C" in Bro IntelliFax 4100. To fix this issue. You will need to pull out the toner. Note: the toner and drum are connected.....At the left corner of the drum. You will see a blue tab......You will need to slide the blue tab back and forth for 20th times....And put the toner back in its place.....This is just a temp fix but you need to replace the drum to have it working its fullest......

Have you tried a new toner cartridge?

sounds like a defective cartridge, if it's a generic toner the seals may not have been replaced, buy a new one and return the other as defective.

change out the fuser unit!

open front cover, press "clear" and 1, that will clear the change drum soon error