Green Line on a Samsung Screen? What to Do

What the line is

Galaxy phones use OLED displays, where each pixel makes its own light. A single vertical line in one colour usually means a column of pixels has stopped being driven properly: a fault in the panel itself or in the fine connections along its edge. Owners of several Galaxy S and Note models have reported lines like this appearing without any drop, sometimes soon after a software update. Others appear after a knock or pressure on the screen.

Whatever started it, the line is in the hardware. Software can't redraw a column of pixels that's no longer connected.

What to try first (it takes two minutes)

Take a screenshot while the line is showing, and look at the screenshot on another device. If the line isn't in the screenshot, the fault is in the display, not the phone's software.
Restart the phone. Rarely, a line that's caused by a software glitch disappears. If it comes back, it's the display.
Install any pending software update, in case it's the rare software case.
Look for damage: a crack near the line, a dent in the frame, or a bulge from the battery behind the screen.

If the line is still there after a restart, plan for a screen replacement.

Is it covered?

Under Samsung's warranty, with no drop or liquid damage: contact Samsung first. A display failure without accidental damage is the kind of fault a warranty is for.
Out of warranty, but the phone isn't old: the Australian Consumer Law expects a phone to last a reasonable time for its price. A display that fails on its own after a short time may still be Samsung's or the seller's problem. The ACCC explains how to ask for a remedy.
Free screen programs: Samsung ran free one-time screen replacement programs for green line faults on some Galaxy models in India. We haven't found a similar program announced in Australia, so don't count on one, but it's worth asking Samsung.
After a drop, or out of time: a screen replacement at a repair shop is the fix.

Can I keep using it?

Usually, yes, for a while. A single line doesn't stop the phone working. But lines often multiply or widen, and some displays go on to fail completely, which makes it hard to get into the phone to back it up. So:

back up now (Samsung Cloud, Google, or Smart Switch to a computer);
don't press on the area around the line;
if more lines appear or touch stops working in places, get it fixed soon.

What a screen replacement involves

On Galaxy phones, the OLED display and the cover glass come as one assembly, often with the frame. The old screen comes off, the new one goes on with fresh adhesive, and the phone's parts move across. Then the screen, touch, the fingerprint reader (on models with it under the display) and the front camera are tested. Your photos and apps stay on the phone.

Replacement screens differ in quality. For a Galaxy with an in-display fingerprint reader, choose an OLED replacement: cheaper LCD screens usually stop the fingerprint reader working and look noticeably greyer.

Sources

Related repairs at Riverlink

Green or Pink Line on a Samsung Screen: What It Means and What to Do