iPhone 4S Recovery Loop With Error -1 and Error 21
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rabski • July 14, 2013 at 1:13am
My iPhone 4S is stuck in a recovery loop. When I try to restore, I receive error -1, and in DFU mode, I receive error 21. I tried using Redsn0w for a recovery fix, but it did not work. Now the device shows the Apple logo and then turns off. iTunes does not recognize it until I enter DFU mode, but the restore process still fails.
Answers
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iClarified • January 14, 2026 at 3:12am
To resolve iPhone 4S recovery loop errors like -1 and 21, start by ensuring you are using the latest version of iTunes or Finder. Error 21 often indicates a hardware timing issue during the restore process. You can often bypass this by ensuring the device is in a true DFU mode and using a high-quality Apple cable. Error -1 is significantly more difficult as it often points to a hardware failure with the cellular baseband chip. Before assuming hardware failure, try restoring the device on a completely different computer and network. If the restore still fails at the same point with error -1 on multiple machines, the logic board likely has a physical hardware defect.