Fix 16xx and 21 Error during iPhone 3.1 Restore in iTunes
When trying to restore your iPhone or iPod touch in iTunes with iPhone 3.1 firmware, you may see the following message followed by an error code 1601, 1602, 16xx or 21:
The iPhone "[your iPhone]" could not be restored. An unknown error occurred.
To get around this problem, iH8Sn0w has released a handy little tool called iREB (iTunes Restore Error Bypasser) for both Windows and Macs which can help bring your iPhone back to life. The latest version of this program supports iPhone 3.1 firmware running on the original iPhone, iPhone 3G and iPod touch 1G.
Step 1: Start iTunes and put your phone into DFU mode:
Press and hold the Home button and the Power button at the same time. After exactly 10 seconds release the Power button. Continue holding the home button until you iTunes pops up a message telling you that it has detected an iPhone in recovery mode. At this point your iPhone/iPod touch screen will remain black.
Step 2: Now close iTunes and Start iREB on Windows or Mac.
Step 3: Simply select your device and wait for a few seconds until you get white or a red screen on your iPhone.
Step 4: Now open iTunes and click on your phone from the sidebar in iTunes to get to this screen as shown in the screenshot below:
Now press and hold left “alt” button (“Shift” button on Windows) on the keyboard and then click on “Restore” (Not “Update”) button in the iTunes and then release the “Shift” button. Select a custom .ipsw file and restore it. Hopefully you wont get any errors this time around!
One thing to note here is that iREB is not for jailbreaking. It is only used for restoring to custom .ipsw firmware files via iTunes without any errors. Check out my guides posted here and here for jailbreaking and unlocking iPhone 3.1 firmware.