External Monitor Not Detected on Mac [9 Solutions]

If your Mac doesn't detect an external monitor, try these steps: 1. Check cables and connections. 2. Restart Mac and monitor. 3. Use Detect Displays in System Settings. 4. Reset NVRAM/PRAM. 5. Try a different port or adapter. 6. Update macOS and firmware. 7. Boot in Safe Mode. 8. Verify display settings. 9. Test with another computer to isolate the issue.

If your external monitor isn't being detected by your Mac, it can disrupt your workflow. Here are several solutions to resolve the issue:

The operating environment of this tutorial: MacBook Pro, macOS Sonoma

1. Check Physical Connections

Ensure that the video cable and power connections between your Mac and the external monitor are secure. Loose or damaged cables are a common cause of detection failure.

• Unplug and reconnect the video cable (e.g., HDMI, DisplayPort, USB-C/Thunderbolt) at both ends
• Inspect the cable for visible damage and replace it if necessary
• Verify the monitor is powered on and set to the correct input source

Use a known-working cable to rule out hardware faults.

2. Restart Your Mac and Monitor

A simple restart can resolve temporary glitches in the display subsystem. Power cycling both devices resets the connection handshake.

• Shut down your Mac completely
• Turn off the external monitor and unplug it from power for 10 seconds
• Reconnect the monitor, power it back on, then restart your Mac

3. Use the Display Detection Feature

macOS can manually search for connected displays. This forces the system to reinitialize the external display connection.

• Click the Apple menu and select System Settings
• Go to Displays
• Hold down the Option key to reveal the Detect Displays button and click it

This function resets the display manager and often detects previously unrecognized monitors.

4. Reset NVRAM/PRAM

NVRAM stores display settings and other hardware configurations. Resetting it can fix incorrect display parameters that prevent detection.

• Shut down your Mac
• Turn it on and immediately press and hold Option Command P R
• Keep holding the keys for about 20 seconds
• Release the keys and allow your Mac to start up normally

5. Try a Different Port or Adapter

If your Mac has multiple video output ports, one may be malfunctioning. Using an alternate port or adapter can bypass hardware issues.

• Connect the monitor to a different Thunderbolt/USB-C port
• If using an adapter (e.g., USB-C to HDMI), try a different one
• Test with another display to isolate whether the issue is with the monitor or Mac

Some third-party adapters lack proper macOS compatibility—use Apple-certified models when possible.

6. Update macOS and Firmware

Outdated system software may lack support for certain monitors or contain bugs affecting display detection.

• Open System Settings and go to Software Update
• Install any available updates for macOS
• Check for firmware updates through System Report > Software

7. Boot in Safe Mode

Safe Mode loads a minimal set of drivers and resets certain system states, which can help identify software-related display issues.

• Shut down your Mac
• Turn it on and immediately hold the Shift key
• Release the key when you see the login window
• Check if the external monitor is detected
• Restart normally after testing

8. Check Display Settings Configuration

Sometimes the external display is active but misconfigured, making it appear undetected.

• Go to System Settings > Displays
• Click on the arrangement tab
• Look for a secondary display icon, even if the screen is black
• Drag the white menu bar to the external display to test functionality

9. Test on Another Computer

Isolating the hardware helps determine if the problem lies with the Mac, the monitor, or the cable.

• Connect the external monitor to a different computer using the same cable
• If it fails to work, the monitor may be faulty
• Connect your Mac to a different monitor
• If the issue persists, the Mac’s video output may be damaged

This diagnostic step is crucial for identifying the faulty component.

The above is the detailed content of External Monitor Not Detected on Mac [9 Solutions]. For more information, please follow other related articles on the PHP Chinese website!