If you downgrade through iTunes back to 4.0.1 (using the saved shsh), you will get your phone locked in recovery mode. Just press the Kick button of TinyUmbrella to continue. But the problem there is that then the baseband will remain on 02.10.04.

To downgrade the baseband back to 01.59.00, just install the latest official firmware from Apple. This is 4.0.2. Don’t install 4.0.1, because for 4.0.1 there are no certificates for the baseband available.

To install 4.0.2, make sure your hosts file is clean and doesn’t contain the Saurik server entry (gs.apple.com). Remove that line, if it is there. Then restart iTunes. If TinyUmbrella was running, close it and check the hosts file again. Make 100% sure that you connect directly to Apple and not to your localhost (127.0.0.1) or to Saurik. If everything is fine, install official 4.0.2 firmware and its baseband. It shouldn’t stop in the middle, requiring the Kick again. If that happens, iTunes probably connected to Cydia and Cydia couldn’t provide the certificate for the baseband.

If you successfully installed 4.0.2 without the need to Kick the device out of recovery loop, then you probably downgraded your baseband successfully also. Activate your phone and then downgrade the firmware back to 4.0.1. Then you can jailbreak and unlock again.

Be aware that this method only works as long as Apple still signs 4.0.2 firmware. They probably stop signing 4.0.2 on September 8, or when firmware 4.1 comes out. So if you are on 4.1 GM and want to downgrade your baseband, do so now. As soon as 4.1 is officially out, use TinyUmbrella (version 4.1.xx, not out yet) to update to 4.1 without updating the baseband.

(Press Thanks button if this helped.)

Related Posts:

• Downgrade baseband with shsh?
• How to downgrade iPhone 3g/3gs/4g baseband?
• UNLOCK – why you SHOULD NOT update FIRMWARE and/or BASEBAND
• 3G Baseband downgrade ?
• NEW iPHONE 3G/3GS UNLOCK – BE VERY CAREFULL!