Error 43 on Mac appears when the operating system fails to communicate properly with an external device or peripheral. This stops the device from mounting and can interrupt workflows, backups, or file transfers.
Below you will find a structured overview of the most common causes, quick checks, and stepwise fixes that help resolve Error 43 quickly and safely.
| Trigger | Likely Symptom | Quick Check | Immediate Action |
|---|---|---|---|
| Faulty cable or port | Device disconnects or never mounts | Inspect for damage; try another USB-C or Thunderbolt port | Replace cable and use a different port on the Mac |
| Incompatible drive format | Appears in Disk Utility but cannot be mounted | Check file system shown in Disk Utility | Back up data and reformat to APFS or Mac OS Extended |
| Corrupted file system | Drive shows as grayed out or inaccessible | Run First Aid in Disk Utility | Repair the disk; if repair fails, back up and reformat |
| Software or firmware issues | Intermittent errors after updates | Check System Settings > General > About for updates | Update macOS and firmware; restart the device and Mac |
Hardware Checks and Connections
Cables, Ports, and Physical Inspection
Start by examining the USB-C or Thunderbolt cable for nicks, bends, or damaged shielding. Swap to another cable and try a different port on the Mac to rule out a single point of failure. Also test the device on another Mac or Windows machine to confirm whether the issue originates from the Mac itself.
Drive Format and File System
APFS, Mac OS Extended, and Compatibility
Error 43 often surfaces when a drive uses an unsupported format for native macOS access. Verify the file system in Disk Utility and, when necessary, reformat as APFS or Mac OS Extended. Remember that formatting erases all data, so always move valuable files to a backup location first before making changes.
Software Updates and System Integrity
macOS Patches and Security Settings
Ensure macOS is up to date, since Apple frequently releases patches that refine driver and peripheral compatibility. In System Settings, confirm that the Mac is allowed to access external drives and that any security settings or configuration profiles are not overly restrictive for the connected device.
Drive Utility and Repair Workflow
First Aid, Rebuilding, and Safe Reformatting
Open Disk Utility, select the external drive, and run First Aid to fix directory and permission issues. If First Aid cannot repair the volume, back up any recoverable data immediately, then erase and reformat the drive using the appropriate scheme and partition layout for your workflow.
Reliable Workflow for External Drives on Mac
- Use high-quality cables and verified ports that support USB 3 or Thunderbolt
- Check System Settings for updates and install pending macOS patches
- Verify the drive file system and run First Aid in Disk Utility
- Back up data before any erase or reformat action
- Test the drive on another machine if problems persist
FAQ
Reader questions
Why does my external drive show up in Finder but still throw Error 43?
The drive may be mounted in a limited capacity while macOS struggles with permissions or the file system. Use Disk Utility to run First Aid, verify the file system, and repair the disk to clear the condition.
Can a failing SSD or hard drive trigger Error 43 on Mac?
Yes, when sectors go bad or the controller reports an issue, macOS may block mounting and surface Error 43. Inspect S.M.A.R.T. status in Disk Utility and consider migrating data to a healthy drive as soon as possible.
Will reformatting the drive remove all my data during Error 43 troubleshooting?
Yes, any erase and reformat operation deletes existing content. Create a complete backup with Time Machine or another tool, then reformat only after safeguarding important files.
Is Error 43 ever related to macOS security policies or Gatekeeper?
It can be, especially with newer external drives that require updated firmware or drivers. Updating macOS and confirming that the device is allowed in Security & Privacy settings often resolves policy-related blocks.