A clean laser print is a sequence of six things going right: the drum is charged evenly, the laser exposes it, toner sticks to the exposed areas, the transfer roller moves toner onto the paper, the fuser melts it, and the drum is wiped for the next page. A streak or line is one of those six steps failing in a narrow strip. The shape of the defect tells you which step. Work through the checks below in order — most streaks are solved in the first two.
Step 1: Print a clean test page
Print a page with a solid black block and a page with only text. Use the printer's own test page (HP: Reports > Print Quality Page; Canon: Cleaning / Nozzle-free "Print Quality" report on imageCLASS). Note the direction of the defect: vertical means along the direction the paper travels; horizontal means across it.
Vertical streaks or bands
Wide, soft, gray band — toner is low or clumped
Remove the cartridge, hold it level and rock it gently side to side five or six times, then reinstall. If the band disappears you had toner settling to one side; you have a few hundred pages left. If it reappears within a day, replace the cartridge. On HP LaserJet Pro models this is the classic end-of-life pattern for cartridges like the HP 58A and HP 26A.
Thin, sharp black line — scratched or dirty drum
A hairline in exactly the same position on every page is a defect on the drum surface. On printers where the drum is part of the toner cartridge (most HP LaserJet Pro monochrome models and Canon 137/045-class cartridges) replacing the cartridge fixes it. On printers with a separate drum unit, such as HP LaserJet Pro M102/M130 with the HP 19A drum, replace the drum, not the toner.
White vertical gap — something blocking the laser or transfer
A white strip where nothing prints means light never reached the drum or toner never transferred in that strip. Open the printer, remove the cartridge and check the laser scanner window (a long narrow glass or plastic strip above the cartridge bay) for dust, and the transfer roller (the black sponge roller under the cartridge) for a stuck label fragment. Clean the window with a dry lint-free cloth. Never touch the transfer roller with fingers; use the paper edge to lift debris.
Horizontal lines or bands
Bands that repeat at a fixed spacing
Measure the distance between repeats. Each roller in the printer has a circumference; a defect on that roller repeats every circumference. Typical values: drum roughly 75–95 mm on desktop LaserJets, developer roller 30–45 mm, fuser 60–100 mm. Consult the service manual for your model, but the practical rule is: short interval = developer or charge roller (inside the cartridge, replace cartridge); long interval near the top of that range = fuser (fuser kit).
Random horizontal streaks
Random bands, worse on the first page of the day, are usually moisture in the paper. Open a fresh ream, or store paper away from the floor and outside walls. Cheap recycled paper also sheds fibers that build up on rollers.
Smudged streaks that rub off
If the streak smears under a finger, the toner was never fused — see our guide on toner not fusing. This is a fuser or paper-setting issue, not a cartridge issue.
Clean the printer before you buy parts
Run the built-in cleaning page (HP: Tools or Service > Cleaning Page; Canon: Cleaning under Maintenance). Vacuum the paper path with a toner-safe vacuum or wipe with a dry cloth; never use compressed air inside a laser printer, it drives toner into the electronics. Replace the paper. Then print the test page again.
When it is time to replace
If the defect survives cleaning and a cartridge reseat, replace in this order: toner cartridge (cheapest, most likely), then drum unit if your printer has one, then fuser. Buy the exact genuine part for your model — use our printer cartridge finder if you are not sure which cartridge your printer takes.
Genuine cartridges mentioned in this guide
Related guides
Frequently asked questions
Why does my laser printer print a vertical line down every page?
A thin, sharp vertical line in the same place on every page is almost always a scratched drum or a hair or paper fiber stuck on the drum, the transfer roller or the laser window. A wider vertical band is usually a low or unevenly distributed toner cartridge.
Do streaks mean I need a new toner cartridge?
Not always. Rock the cartridge gently side to side and reinstall it; if the streak fades you are near the end of the toner. If the line is sharp and stays exactly in place, the drum or a roller is the cause.
Can dirty rollers cause horizontal lines?
Yes. Horizontal lines or bands that repeat at a fixed interval point to a roller — the interval tells you which one. Bands at random positions usually mean paper dust or humidity.
