Hp laserjet printer one side too light printing.....just like a wide line up to down.....

check the fusing unit in the rear of the printer and check your print cartridge for smudges.

Replace toner cartridge. If problem persist replace fuser unit. P/N # RG5-5559

Generally speaking, any area that is darkened, is receiving less light. This can come from a lamp that is failing (similar to a fluorescent lamp used for lighting developing a dark end) or a mirror or optical lense that is contaminated with toner.
This may require some disassembly to diagnose and cure.
You may also want to visually check the fuser assembly (often accessible behind a door) to ensure there is no toner buildup on the affected side.

try to set the margins

the printer would print but a line with missed ink would be going down the right side of the paper

Change the toner cartridge, refilling will not solve the problem.

Run a half test. Start printing a few pages, as it prints open the cover, remove the toner and look down at the paper. Does it have lines on the right side? If yes - replace the toner cartridge.

try to change the toner first and if the problem is not sloved you can clean the fuser and check again then you can go for a fuser change

your toner drum coating eject
change toner drum

Maybe your transfer belt is damaged. If u have an spare belt replace it for a test. Answer me if it dont work. Maybe i can get an support manual for u. I work in a HP partner company.

Good luck