How to Downgrade iOS 4.0.2 to iOS 4.0 or 4.0.1

Upgrading to the recently released iOS 4.0.2 to fix the PDF problem brought about by Comex’s JailbreakMe will make you loose the jailbreaking and unlocking you’ve done on your iPhones.

Only iPhone 3G and iPod Touch 2G (non-MC) users can jailbreak and unlock iOS 4.0.2. So if you want to go back to having a jailbroken and unlocked phone, the solution is to downgrade to iOS 4.0 or 4.0.1 then re-jailbreak your iPhone using JailbreakMe.

Before proceeding with the downgrade, ensure that you saved your SHSH blobs for iOS 4.0 or 4.0.1. After checking on this, follow the instructions herein provided to proceed with the downgrade.

1. Download the iOS 4.0 IPSW or iOS 4.0.1 IPSW file required for your iDevice and place it on your desktop.

2. Put your iPhone in DFU mode by:

* Starting iTunes and connecting your device to your PC/Mac with USB cable.
* Turn off your device.
* Hold the Home and Power button for about 10 seconds, then release the Power button but keep holding the Home button until iTunes detect your iPhone in recovery mode. Your iPhone screen should be totally blank by now.

3. Edit Windows / Mac HOSTS file:

For Windows Users:

* Navigate to Start >All Programs > Accessories > Right click on the Notepad icon > Choose Run as Administrator
* Now go to File menu in opened Notepad and choose Open or simply press Ctrl+O.
* Browse to C:\Windows\System32\drivers\etc and open HOSTS file.
* Once HOSTS file is opened, copy-paste the following line at the end of the file:
74.208.105.171.apple.com
* Now, go back to File menu and choose Save or press Ctrl+S.

For Mac Users:

* Click Go > Go to Folder and then enter path /etc
* Open HOSTS file with TextEdit and add the following line at the end of the file:
74.208.105.171.apple.com
* Now go to File and choose Save As, uncheck if no extension is provide, use .txt and save the HOSTS file on your desktop.
* Now replace the original HOSTS file with the one you just saved on your desktop. In case you are prompted for the password, just enter it and click OK.

4. After successfully editing your HOSTS file, open iTunes and click on the name of your device from the sidebar menu.

5. On the summary page, hold down the SHIFT key on keyboard and press Restore button. Choose the firmware file you want to restore, choose the respective(iOS 4.0 or iOS 4.0.1) IPSW file you downloaded in step 1. For Mac OS X user, use the ALT+Restore combo to choose the firmware file.

6. iTunes will now restore the firmware files on your device. Your iPhone screen will show you the restore progress. Just in case iTunes shows errors with code 1015, 1013 or 1011, just ignore them.

7. After the completion of the restore process, download Recboot. Recboot is a free utility for Windows and Mac users which forces an iDevice to exit from recovery mode with a single click. Click on the Exit Recovery Mode button to restart your device.