How to Downgrade iOS 4.2.1 to iOS 4.1 / 4.0.2 / 4.0.1 on iPhone 4, 3G, 3GS, iPad and iPod touch [Tutorial]

iOS 4.2.1 has released for iPhone 4, iPhone 3GS, iPhone 3G, iPod touch 4G, iPod touch 3G, iPod touch 2G and iPad. iOS 4.2.1 contains new baseband for all iOS devices which makes it impossible to jailbreak. Now we are going to show you step by step instructions to downgrade iOS 4.2.1 to iOS 4.1 / 4.0.2 / 4.0.1 on iPhone 4, 3G, 3GS , iPad and iPod touch. If you upgraded to iOS 4.2.1 then you can downgrade back to iOS 4.1 / 4.0.2 / 4.0.1. Follow the steps carefully.

NOTE: You should have SHSH blobs saved for the respective firmware you downgrading to.

INSTRUCTIONS

STEP 1. Download the required old ipsw firmware files. (Download iOS 4.1, iOS 4.0.2, iOS 4.0.1)


STEP 2. Now put your device into DFU mode

• Connect your iPhone to the computer
• Turn off your iPhone
• Start iTunes
• Hold Home and Power buttons together for 10 seconds
• Keep holding the Home button until your computer recognizes a new USB device and release Power button
• Now iTunes will recognize your iPhone

At this time your iPhone screen should be blank
(Skip Step 3 and continue from Step 4 if you are on iPhone 3G or iPod touch 2G (non-MC model))
STEP 3. This step is for iPhone 4, iPhone 3GS, iPod touch 3G and iPod touch 2G (MC model). You should have your SHSH files saved on Cydia for the firmware you downgrading on otherwise you cannot downgrade.

• Navigate to C:\Windows\System32\drivers\etc\ and locate “hosts” file

Mac OS X users can get to “/etc/” directory by going through “Go –> Go to Folder” from Finder.

• Open this “hosts” file in Notepad (for Windows) or TextEdit (for Mac OS X) and add this line

74.208.105.171 gs.apple.com

As shown in the image below:

Now simply save this file.
For Mac OS X: You should have full write and read access on your account when you are saving the host file. If it still shows permission error, simply copy the host file to desktop, make the required changes, and then replace it with the original file in “/etc/” directory.
For Windows 7 and Vista: Start “Notepad” with Administrator privileges by right clicking on “Notepad” app, and click on “Run as Administrator“ option.


STEP 4. Now you will have to restore your iPhone, iPod touch or iPad to the firmware you downloaded in Step 1. Then click on your iOS device icon from the sidebar in iTunes. Now press and hold left “alt” button on Mac (Left “Shift” button on Windows) on the keyboard and then click on “Restore” button in the iTunes and then release this button. (Do not “Check for Update”)





Now iTunes will prompt you to select the location for your downloaded firmware file. Select that ipsw file and click on “Open”.


STEP 5. Now iTunes does the rest for you. Wait for sometime while iTunes installs the requested firmware on your iPhone. A progress bar indicating installation progress will be shown on your iPhone screen. At some points iTunes will throw 1004 or 1015 error. You should ignore this error as the firmware has already been installed on the device successfully.







STEP 6. At this point your iPhone will be stuck in Recovery Mode and shows “Connect to iTunes” screen. To exit your iPhone from Recovery Mode, download TinyUmbrella (Mac / Windows), run it and then click on “Exit Recovery” button. Now your device will restart normally.





That’s it, now you should be able to jailbreak your device on iOS 4.0.x with JailbreakMe and jailbreak your device on iOS 4.1 using Limera1n. After you have jailbroken your device, you can follow our step by step instructions posted here to unlock your iPhone on iOS 4.x, on older baseband using Ultrasn0w. Stay tuned with us for more updates.


STEP 7. Now you must remove 74.208.105.171 gs.apple.com line from the host file so that you are prompted for future updates from Apple via iTunes