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How To Downgrade iPhone 3GS IOS 4.2.1

by Alvin on December 14, 2010

Accidentally updated your iPhone 3GS to IOS 4.2.1 through iTunes? Although IOS 4.2.1 is still jailbreakable using redsn0w, but the jailbreak for iPhone 3GS with new bootrom is tethered only. Every time it restarts, you need to run redsn0w to boot it again. This can be very troublesome especially when you’re working or studying. You can’t use your iPhone 3GS until you get a PC to run the redsn0w. If your iPhone 3GS has SHSHs on file for iPhone IOS 4.1, you can downgrade it to IOS 4.1 through iTunes and then jailbreak your iPhone 3GS IOS 4.1 using either redsn0w, limera1n or greenpois0n.

Check Your iPhone 3GS has an ECID SHSH on file

Most of the jailbroken iPhone should have the SHSHs on file for iPhone IOS 4.1 or below. If you noticed that Cydia indicated your iPhone 3GS has SHSH IOS: 3.1.2, 3.1.3, 4.0, 4.0.1, 4.0.2, 4.1, then it can be downgraded to any of IOS listed on Cydia.

SHSH IOS: 4.0, 4.1

Check Your iTunes Is The Latest Version

Follow this step-by-step guide to check and update iTunes on your PC  if it’s not the latest version.

Add gs.apple.com To Windows Hosts File

Before you can shift restore your iPhone 3GS to IOS 4.1 through iTunes, you need specific the hostname (Saurik’s server) in order to redirect Apple’s signature server to Cydia. Run c:\windows\System32\drivers\etc\hosts, open with Notepad and add the following entry to last line of the file. gs.apple.com


Restore Your iPhone 3GS In DFU Mode

Download iPhone 3GS IOS 4.1 and follow this step-by-step guide to restore your iPhone 3GS to IOS 4.1. Please select IOS 4.1 when the windows pop up.

Quick Tips: Put Your iPhone into DFU Mode

  • Connect your iPhone 3GS while it’s switched on to your computer
  • Hold both sleep/wake and home buttons simultaneously, release only sleep/wake button (still holding home button) until your iPhone 3GS disconnected from iTunes.
  • While you still holding home button, wait iTunes/computer to detect your iPhone 3GS in DFU mode.

Solve iTunes Error Code 1015

You’ll get iTunes error code 1015 and see the iTunes with USB cable on your iPhone 3GS (in recovery mode) after it has been successfully restored to IOS 4.1. Download RecBoot 1.3 and run it to exit the recovery mode.

Jaibreak Your iPhone 3GS IOS 4.1

Follow this step-by-step guide to jailbreak your iPhone 3GS IOS 4.1 using limera1n.

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