How to fix Laser Printer thats printing faded printouts?

Well, it's most probably bad toner cartridges since they're remanufactured and not original manufacturer or new ones, but there is another possibility to verify first.

Did you remove the toner cartridge sealing tape from them when you installed them?

There is usually a plastic tab with a long strip of sealing tape attached, or just a piece of sealing tape hanging out of the cartridge (sometimes it's just a solid platic shield that is pulled out), that needs to be removed completely to allow the toner in the toner hopper to reach the mag roller & drum surface. Often times there's just enough toner on the rollers to print a little, but then it's all used up and starts printing light until that sealing tape is removed.

If you did remove the sealing tape and you still have this problem, then I'd get in contact with the seller where you purchased the cartridges from to get them replaced or refunded.

My first guess here would be you have bad toner cartridges. With remanufactured, you're taking chances because they may have been filled correctly or done badly. Or it could be the sealing tape that prevents toner from spilling out during shipping, etc may not have been fully removed. For example, if it tore and portions of it still attached to the cartridges. Another thing it could be is a bad fuser. Each color, including black, has it's own. And that's what heats up to attach the toner to the paper. If it's not heating up enough, then the toner won't stick to the paper. But these tend to last quite a long time. So that would be my last guess, not at the very top.

So I would say it's most likely bad black toner cartridges. And I would suggest you try to get them to send you replacements. Or have them refund your money. It's not uncommon for people to have troubles with remanufactured ink cartridges for inkjets or toners for lasers. Some places do it right and you don't have problems. But others aren't so careful and you end up with problems. Problems like the one you're having. Or worse ones like toner or ink actually leaking out and getting all over the machine itself! Or the toners / inks not lasting as long as the originals. And even poor output quality due to substandard toner or inks.

Sounds like the imaging unit on your printer is going out or the fuser. either way the its going to be expensive to fix i doubt its the toner cartridges. The best thing you could possibly do is get a clean rag (perferably micro fibre) and clean the imaging unit belt (its green) with alchol or windex use A CLEAN CLOTH though.