Apple has just released iOS 4.3 for the iPhone 4, iPhone 3GS, iPod Touch 3G, 4G, and iPad to developers.If you accidently updated your firmware to the new iOS 4.3, you can use the guide below to downgrade your firmware back to either iOS 4.2.1 or iOS 4.1.
Keys To Be Noted
Guide only works if you have your iOS 4.2.1 or iOS 4.1 firmware SHSH blobs saved
If you are still on iOS 4.2.1, we highly recommend you to save the blobs before upgrading iPhone to iOS 4.3. You can either use TinyUmbrella on Windows and Mac Systems or iSHSHit app on your iPhone.
The steps are as follows:
Step 2: Navigate to the path “c:\windows\system32\drivers\etc\” and open the hosts file in a Notepad or Wordpad. MAC users can navigate to the path “/etc/” and open the hosts file with TextEdit.
If you are Mac user, navigate to GO -> Go to Folder and enter the path “/etc” and open the file “hosts” with TextEdit.
Step 3: Now add the following hostname at the end of the file as shown in the screenshot below. Save the file.
Step 4: Now, open iTunes once again and connect your device with the PC via USB cable and put your device into DFU mode. Here is how you can get DFU mode on your phone.
* Turn off your phone.
* Now press Power button and as soon as you seen Apple Logo, press Home button while keeping pressed Power button too.
* Keep holding down both button for about 10 seconds.
* After 10 sec, release Power button but keep holding Home button until iTunes recognizes your iPhone. You should keep the PC volume high to hear New Device Detection sound.
* Let go the Home button. At this point your iPhone screen should be blank (black in color).
Step 5: From the iTunes sidebar select your device. Now press the “alt” (option) button on Mac or left “Shift” button if you are on Win and then click on “Restore” button in the iTunes.
iTunes will prompt you to choose the location of your ISPW file, navigate to the place where you downloaded the ISPW file (of previous iOS) and choose that.
Now, just sit back and relax while iTunes does the work for you. While the process might complete you might encounter the 1013 error, if you do so, just ignore it as everything is perfectly fine in the background.
At this point your iPhone may be stuck in recovery mode, showing that “Connect to iTunes” screen. To get rid of this recovery mode, download TinyUmbrella and click on “Exit Recovery” option.
That’s it! You successfully downgraded to iOS 4.3 to iOS 4.2.1, 4.1, 4.02, 4.01 firmware.