Copy has a white 4" strip down the middle I have a canon k940

Question edited for maker and to make a proper question.
Question moved from Television and Video category.

All question need FULL 'make model (what it is)'. ImageCLASS covers about 40 models of different sizes and features.

The most likely reasons are;
White Out in the document feeder scan strip.
Torn paper somewhere in the paper path.
A bad developer roller.

if its not the cartridge then its the fuser. buy a new copier, cheaper than fixing it.

Hi Ben,
Please Watch This video and fix your issues.

In Case You Still face Problem and Need Online Assistance Then Please Follow Us For On : Canon Printer Support

I suggest You Go to Official Canon Printer Page For You Canon Problem On Below Canon Page URL:
Copy Has Vertical Black Streaks In Case You Still face Problem and Need Online Assistance Then Please Follow Us For On : Canon Printer Support

They are manny cause of black copy.
1.over tone.
2.arching on main charger or dirt on main charger.
In Case You Still face Problem and Need Online Assistance Then Please Follow Us For On : Brother Printer Support

There is something on your scan glass. My guess is you are getting the line on your copies when you run the original through the document feeder. If you get lines through the document feeder but not on copies made off the glass then it is a dirty scan glass. There is a thin glass strip where the document feeder feeds the original. Usually something like white out that did not dry smears off an original and ends up on this thin strip of glass. Scratch it off with your finger nail and use some glass cleaner to resolve the problem. The scan glass is about 1/2 an inch to an inch wide and will be on the same side of the machine that the copier feeds the originals in on.

what your copir model? if your model IR3045 replase the drame unite.

if you are using dadf ? try to clean the small glass on the laten cover

It's hard to say when I don't know what machine you have, but it could be the toner cartridge. If you have a cartridge pull it ou shake it gently and try another copy.
Good Luck

Try replaceing the cartridge the toner has run out.
Any problems please get back to me.
Thank You