Monday, 27 February 2012

MOBILE --> iphOnE eRrOr 21 aNd SoluTion

iPhone Error 21 and Solution ~~>

iPhones can give you many errors. And, if you are downgrading your iPhone then you might have encountered Error 21. So, do you get this Error 21 frequently?
iPhone Error 21

If yes, then the problem is, instead of landing in Device Firmware Upgrade (DFU) mode you are ending up in Recovery mode.
Now, if you can get back to DFU mode that will solve your problem. Once the iPhone is in (DFU) mode, you can follow the following process to downgrade your iPhone.


When the iPhone is in DFU mode, this mode will bypass the operating system that is currently installed. This process aids in downgrading or upgrading your Operating System in iPhone. Remember, DFU mode is different from the usual Recovery mode.
The difference between the two modes can be spotted below:
iPhone Error 21

Here, you can see there is no backlight and the screen is blank and black. This indicates that the phone is in DFU mode.
In the figure below, you can see a cable connecting to iTunes icon on the screen. This indicates that the screen is in Recovery Mode.
iPhone Error 21

If there is something on the screen, then that means you are not in the DFU mode.
You have a process that can load the iPhone in DFU mode. Check out that process here:
  • First, you need to plug in your iPhone to your Computer.
  • Now, turn your phone off.
  • Now, for the span of 10 seconds precisely, hold the Power and Home buttons together.
  • Now, continue holding the home button and release the power button.
  • This has to be done until you hear a beep sound from your Computer
  • Now you should see a blank screen sans any display. This indicates that you are in DFU mode.
  • Now your restore should work accurately.
If you are having trouble with the 10 seconds time frame, then try adjusting the time to fewer seconds as per your requirement.
So, next time if you have trouble with Error 21, then try restoring the iPhone with this process.


  1. I Had error 21.
    I took my phone to the Apple store yesterday and it actually turned out to be a bad battery connection. The connector was bent, making contact but screwing up the memory. My second battery replacement on my iPhone 4. $89.00 This absolutely and instantly fixed the problem. Please let me know if this helps . I just created an account so I could answer your question.The Apple guy did tell me he had to put it in UDE/UFE mode which doesn't matter a bit if you're not there getting the battery. I see it mentioned on forums a lot, followed by people saying it didn't work.To re-iterate, he said it would have done nothing for me on my own. For me..error 21 was caused by a bad battery

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