How to fix horizontal or vertical lines on Mac's screen [2025]

My MacBook screen suddenly displayed colored lines—a terrifying sight! After frantic online searches and consultations with Apple repair experts, I discovered overheating was the culprit. A temperature control app saved the day. While not all screen line issues are so easily resolved, here are six troubleshooting steps you can take before resorting to costly professional repairs (up to $800!).

Problem Source	Solution	Steps
Overheating	Monitor & Control Temperature	Use iStat Menus to track temperatures and manage fan speeds.
External Display Issues	Test with External Monitor	Connect to an external display to isolate the problem (internal display or graphics card).
Software Conflicts	Run System Maintenance	Use CleanMyMac to execute recommended maintenance tasks.
Power Management Problems	Reset SMC	Reset the System Management Controller (SMC) – instructions vary by Mac model.
Cable/Connection Problems	Check Connections	Inspect and reseat all cables; try different cables and ports.
Hardware Failure	Run Apple Diagnostics	Run Apple Diagnostics to obtain diagnostic codes indicating hardware issues.

iStat Menus: This app provides real-time monitoring and control of your Mac's temperature and fan speeds, preventing overheating. Available on Setapp.

Why Those Pesky Lines Appear

Vertical or horizontal lines, in various colors (green, purple, black, yellow, or multicolored), can stem from three main causes:

• Physical Damage: The toughest to fix independently. (See the section below.)
• Hardware Problems: Often due to fan failure, overheating, damaged display cables, or faulty soldering.
• Software Issues: May involve power management software, graphics drivers, or software conflicts.

Six Self-Help Solutions

Even if you're a Mac novice, these solutions are worth a try:

1. Check Your Mac's Temperature: Overheating is a frequent culprit. High temperatures (above 192°F) can cause screen artifacts. Use iStat Menus and AlDente Pro (for battery temperature management) to monitor and control temperatures.

   

2. Test with an External Display: Connecting to an external monitor helps determine if the issue lies with the internal display or the graphics card.

   

3. Run Maintenance Scripts: CleanMyMac's maintenance scripts clear system junk, including graphics driver caches, potentially resolving software-related issues.

   

4. Reset the SMC: The System Management Controller (SMC) manages power and temperature. Resetting it can resolve various issues. Instructions vary depending on your Mac model.

5. Check External Display Connections (If Applicable): Ensure cables are securely connected, undamaged, and ports are clean. Try different cables or ports.

6. Run Apple Diagnostics: This built-in tool detects hardware problems and provides diagnostic codes. (Instructions vary by Mac model—Apple Silicon vs. Intel.)

   

Is it Physical Damage?

If the above steps fail, physical damage may be the cause. A crack might not be immediately obvious.

Expert Advice (from Mike, a repair specialist): Replacing a damaged display is possible DIY, but risky unless you're experienced. Costs range from $300-$800 for professional repair.

Should You Tolerate Screen Lines?

Generally, no. Hardware problems can worsen. However, if caused by physical damage, using an external display temporarily might be a viable solution.

Summary of Solutions:

• Address overheating with iStat Menus and AlDente Pro.
• Run CleanMyMac maintenance scripts.
• Reset the SMC and run Apple Diagnostics.
• Thoroughly check external display connections.

Setapp offers these apps and many more for Mac and iPhone with a single subscription. Try it free for 7 days!

FAQ: (Answers provided within the article's body.)

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