Okay so the big problem is that when you upgrade to the latest and greatest firmware from apple it updates your baseband in your phone, if you then try and downgrade to a previous firmware (3.1.3 – IPSW file) it will give you a 1015 error and will be stuck in a recovery mode loop.
I have posted the entire process below, and from this you should be able to restore your iPhone 3GS back to 3.1.3.
- Open iTunes
- Attach you’re iPhone or iPod
- Turn Off the device
- Hold the Home Button in and press the On button (hold the Home button in BEFORE you push the the On button)
- Keep pushing those 2 buttons for around 10 seconds
- You will see the Apple logo but you still need to hold the two buttons
- The device will restart again, a few seconds after you see the Apple logo, and will shutdown.
- Now, hold push the On button of you’re device.
- iTunes will alert that a device is attached
- Press alt and click Restore and locate your 3.1.3 firmware IPSW file (download link below)
After the firmware has been installed it will throw up an error, complaining about 1015 or something and the iPhone will be stuck in recovery mode. The OS is actually correct now, but you just need to give it a little nudge, to-do this use iRecovery (download link below)
- Close down the error in iTunes.
- Make sure the irecovery program you have downloaded is in your working directory so you can run it.
- Open up terminal
- Run the following command to get into “iRecovery console mode” and connect to your iPhone :-
./irecovery -s
- Once you are in irecovery console you need to run the following commands :-
(then from the console)
setenv auto-boot true
saveenv
/exit
After this reboot your iPhone with home and sleep and it will now boot into 3.1.3 as normal.
If you took a backup, after the repair iTunes will ask if you want to restore the backup on your device.
Download Links
iPhone 3.1.3 Firmware, google if you need another firmware (CHECK YOU HAVE THE RIGHT ONE!) (Download)
iRecovery for Mac (Download)
iRecovery for Windows (Download)
If this breaks your iPhone, then I won’t be responsible, but I have tried this as well as a few friends and it’s saved our little iPhones 
Bagwaa
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awesome post, you should check out my wp as well http://reallifesdsu.wordpress.com/
thank you so much you helped me out a lot
I’m not passionate about mobile phones. But the knowledge you write here very specific and clear. Thank you so much.
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Thanks for this mate – helped me out of a bind. I’d advise everyone to hold off the 4.0 software for now, it’s buggy for daily use and it’s not really worth it until the app developers update their code anyway.
Thank you, worked like a charm.
I’m back to 3.1.3 and i’m stabble again.
I guess I’ll need another iPhone for development purposes, hehe.
Thanks!
Worked perfectly, thanks very much!
Worked great for me, thanks
You are a legend! Thanks a lot. I have been so frustrated with the bugs in OS 4 hopefully they sort them out soon as the new features are great.
i had never really used terminal before but with these instructions and a quick read through http://guides.macrumors.com/Terminal to know were my “working directory” is was all i needed.
thank you!
question, everyone who has tried downgrading to OS 3.1.3 only on a Mac os? or has anyone been successful downgrading using Windows?? I’ve tried with a Mac and I am getting an error in Terminal.
Thanks heaps,
Don’t bother with OS 4 yet, buggy slow and not worth it especially if you are on a 3G as without multitasking its not that special
I downgraded from OS 4.0 Beta 3 to 3.1.3 as it wasn’t running properly and I couldn’t restore 4.0 B3 again. Any help on going from 3.1.3 to 4.0 B3, I have Xcode as well but it’s isn’t working. My Baseband is on 05.13.04.
Any help is appreciated.
Thanks in advance.
But, how to downgrade baseband to 05.12.01?
I’m on 3G, and I was now on 3.1.3, but my baseband is still 05.13.04 and unlock is imposible for now.
What I can to do?
your awesome man thanks for that , you saved me a lot of time
a big thank you from me too. my battery was suffering with the ios 4.0. i restored phone perfectly with your instructions. only thing is, i couldn’t restore any backups that were made using 4.0. had to restore from a backup which i did just before i upgraded to 4.0. a small price to pay for a stable phone. thanks again!
Hi,
this looks really good. I have an Iphone 3gs on the IOS4.0. Will i be able to get it down to 3.1.3 with this tutorial?
I couldnt add “setenv auto-boot true
saveenv
/exit”
someone please help me
I have error message
The iPhone”iPhone” could not be restored this device isn;t eligible for the rquested build after itunes extracting sofware… what should i do?
Does this keep u jailbroken?