Downgrade from 4.0.2 to 4.0.1 firmware without SHSH Blobs on iPhone 4 3GS

It is possible for some users that they didn’t save SHSH Blobs on 4.0.1 or earlier firmware which allows them to downgrade from 4.0.2 firmware or any higher version in future so that iPhone 4 3GS 3G remain jailbreakable with JailbreakMe. The users who are getting new iPhone 4 are also out of luck because it is being shipped with 4.0.2 firmware. It means until new tool emerges to jailbreak 4.0.2, they have to stay out of jailbreak community.

Update:It turns out to that solution will work for those who have SHSH Blobs.  It is recommended to avoid.

A method to downgrade from 4.0.2 firmware to 4.0.1 firmware has surfaced in wild which works even if you haven’t saved SHSH Blobs. It can be a big news as Prominent Devs state that it is impossible to downgrade without SHSH Blobs. Apparently, you can downgrade 4.0.2 to 4.0.1 or 4.0 firmware as they are similar. There are some random reports of success using this method to downgrade from 4.0.2 to 4.0.1 firmware. It hasn’t been tested but you can try at your own risk as you are already stuck at 4.0.2 firmware without SHSH Blobs.

Here is how to proceed with Downgrading 4.0.2 to 4.0.1 firmware on iPhone 4 3GS.

1. Download 4.0.1 Firmware and 4.0.2 firmware for iPhone.
2. You have to extract the IPSW file to some folder using a utility like 7-Zip or any other Compressor Handler.
3. Open files buildmanifest.plist and restore.plist with a Text Editor like Notepad. Use Search and Replace feature to substitute 8A306 with 8A400.
4. Open the already downloaded 4.0.2 firmware with 7-Zip or any other utility. You don’t need to extract it.
5. Grab all the files from extracted 4.0.1 firmware folder and drop them in the opened 4.0.2 firmware Window which
6. Then delete all the dmg files that end with 002. Be careful, don’t delete dmg files with 001 at end.
7. Save the iPSW file and Connect your iPhone 4 3GS in DFU mode. [How To]
8. Then restore to the 4.0.2 firmware which has been just saved.

[Via BigBoss and PMI]

If this works out then you can proceed to jailbreak iPhone 4 3GS by using following guides.

Jailbreak iPhone 4 | Jailbreak iPhone 3GS 4.0.1

Jailbreak How to [4.0/4.0.1 firmware] for Other Devices

Jailbreak iPod Touch 4.0 | Jailbreak iPad 3.2.1

The jailbreak guides for current iOS 4.0.2

Jailbreak iPhone 3GS 4.0.2 [Old Bootrom] | Jailbreak iPhone 3G 4.0.2

Our analysis regarding upcoming Jailbreak 4.0.2

Jailbreak iPhone 4 4.0.2 | Jailbreak iPod Touch 4.0.2 | Jailbreak iPad 3.2.2

We also put down some thoughts regarding Jailbreak 4.1 for iOS 4.1 to be revealed on Apple September 2010 Event

Jailbreak iPhone 4 4.1 | Jailbreak iPhone 3GS 4.1 | Jailbreak iPhone 3G 4.1 [Guide]

The tools expected

Spirit Jailbreak 4.1 | Jailbreakme 4.1