Apple Error 21 — Causes & Fix
On Apple devices, Error 21 means the restore failed during the DFU/recovery process, often linked to a USB, security-software, or battery/hardware issue.
- Applies to
- Apple devices
- Time to fix
- 10–45 minutes
What it means
Causes include a faulty cable/USB, blocking security software, a drained battery, or a hardware fault. This is a Apple error; if it persists, Apple's official support has device-specific steps.
Symptoms
- "...error (21)." during a DFU restore
- Restore fails in recovery mode
How to fix it
- 1
Charge, change cable/port, disable security software
1. Charge the device, use a genuine cable/port, and disable third-party security software.
- 2
Retry the DFU restore
1. Retry; persistent failures can point to the battery or other hardware.
Frequently asked questions
What causes error 21?
A restore failure, often USB/security-software related, sometimes a weak battery. Charge the phone, use a genuine cable, disable security software, and retry.
Last updated July 20, 2026
Guidance only — always consult a qualified professional or the official service manual before carrying out repairs.