Step 1: Download 4.0.1 ipsw
Step 2: Extract it with winrar or winzip to a folder on the desktop. You may need to rename the firmware file from .ipsw to .zip to do this.
Step 3: Open the buildmanifest.plist with the notepad. Search and replace all – 8A306 with 8A400. Save. Repeat the same with the file restore.plist
Step 4: Download 4.0.2 ipsw and open this with winrar or winzip.
Step 5: Take all the files from the 4.0.1 and drag them over to the 4.0.2 zip archive that you have open.
Step 6: Delete all the dmg files that have 002 at the end, leaving only the 001 files left.
Step 7: Save the archive. And rename it back to .ipsw if you changed the name to get winrar/winzip to open it.
Step 8: Optional: (this helps ensure you get an SHSH file request for the future, but should not be necessary to just restore 4.0.1). Add the 74.208.10.249 gs.apple.com line to the host file (you may follow our previous post on how to do this).
Step 9: Put the device into DFU mode, open iTunes and restore the firmware you changed. Wait for a while and it will restore your iPhone to iOS 4.0.1
Note: this only works due to the similarities in 4.0.2 to 4.0.1 and 4.0. This will not be a way to downgrade to 3.1.x and may not work in future firmware updates.
Voila! The downgrade from iOS 4.0.2 to iPhone iOS 4.0.1 is successfully completed. You can now jailbreak your iPhone 3GS with jailbreakMe and carrier unlock with ultrasn0w easily.
The methods works! CodeBlue himself tested it on his iPhone 3GS and iPod Touch 3G MC.
iPhone 3GS (32 gig) WHITE running 4.0.2:While downgrading iOS 4.0.2 to iOS 4.0.1 firmware you might stuck with error 1015 in iTunes. To fix or troubleshoot error you may try the following guides:
I managed to downgrade a fresh iPhone 3GS running 4.0.2 back down to 4.0. How you may ask? honestly, I do not know. Apple, as we all know, stopped signing the 4.0 firmwares which forced you to update your firmware to a higher version. We all know the infamous SHSH or Blobs. Cydia managed to make “your life easier” and backup your blobs along the way through your jailbreaking life. And TinyUmbrella, helps you store your blobs locally or remotely request to store or to receive your blobs.
Story is, I used TinyUmbrella (umbrella-4.01.01) and downgraded WITH NO LOCALLY STORED BLOBS ON MY COMPUTER AND NO BLOBS ON CYDIA FOR THIS DEVICE. And somehow, I managed to get back down to 4.0. Using iTunes Shift and Restore feature.
I have had another beta tester to test his iPhone 3GS with new bootrom and his iPhone was never jailbroken before and he was running 4.0.2. I gave him my steps and at first attempt failed, yet he tried once more and it was successful. He successfully jailbroke his phone also.
iPod Touch 3G MC (32 gig) running 3.1.3:
I was curious and tried my method again for this ipod touch. now this one is my best proof of all in my honest opinion. This iPod never had been jailbroken before nor has it ever seen 4.0. THIS IPOD WAS FRESH. I knew that if I wanted 4.0 firmware, Apple won’t allow me because they stopped signing this, instead they will force me to 4.0.2. So I tried my method again, and first attempt failed again. So i closed iTunes, disconnected iPod Touch, turned off TSS server and rebooted the TSS server and brought up iTunes with my iPod once again plugged in.
Tried my method, and guess what…. it worked….. I avoided the signing rejection from Apple and I’m at 4.0 and jailbroken.
That being said, I want to remind you again that my desktop computer never touched an iPod or iPhone before meaning TinyUmbrella is completely new to this computer and I have no Blobs/SHSH stored on this computer or anywhere else such as Cydia AT ALL.
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