Error 21: Hardware Issue Detected
This error indicates a potential hardware issue with your iOS device that is preventing the update or restore process from completing successfully.
- • On Mac with macOS Catalina 10.15 or later: Ensure your Mac is up to date
- • On Mac with macOS Mojave 10.14 or earlier: Ensure you have the latest version of iTunes
- • On PC: Ensure you have the latest version of iTunes or the Apple Devices app
- 1 Hardware errors may indicate physical damage requiring professional repair
- 2 Backup your data if the device is still accessible
- 1 Hardware malfunction in the device
- 2 Issues with the logic board
- 3 Faulty connection between device and computer
- 4 Incompatible or damaged USB cable
Understanding Error 21
Error 21 belongs to the hardware error range (20-56) and indicates a potential hardware issue with your iOS device. Like other hardware errors such as Error 1 and Error 3, it typically points to a logic board or connection problem.
Step-by-Step Troubleshooting
1. Verify All Connections
- Use an original Apple USB cable in good condition
- Try a different USB port directly on the computer
- Ensure the cable clicks firmly into the device’s port
- Clean the device’s charging port if needed
2. Restart Everything
- Quit iTunes or Finder
- Force restart your device
- Restart your computer
- Reconnect and try again
3. Check Security Software
Temporarily disable antivirus and firewall software, then retry the restore.
4. Try Recovery Mode
Put your device into recovery mode and attempt a restore. Choose Update first to avoid data loss.
5. Try DFU Mode
If recovery mode doesn’t work, DFU mode may allow a deeper restore that bypasses some hardware checks.
6. Try a Different Computer
If Error 21 also appears on a different computer, the issue is with the device hardware.
When to Seek Professional Help
Error 21 in the hardware range (20-56) often requires professional diagnosis:
- Logic board issues — the most common hardware cause
- Storage chip failure — NAND flash degradation
- Connector damage — internal flex cable disconnection
Visit an Apple Store or Apple Authorized Service Provider for repair options.
Related Articles
Related Errors
Other Hardware Issues
If you've tried all the steps above and still can't resolve the issue, you may need to contact Apple Support or visit an Apple Store. You can also compare your case against Apple's official iOS update and restore errors page.