FP4 - bootloader relocking problems

I have got myself probably in quite a bad pickle. I followed the instructions on the iode website to the letter for installing the custom rom coming from the original OS. And in the end I tried to relock the bootloader, which kind of worked. Then I got the same message saying the device is corrupted and now I am in the bootloader menu, with a locked bootloader and seemingly no way to start the devices, as fastboot does not recognize it.
Is there any solution for that or did I just brick my phone?
Help is very much appreciated:)

Did you do it exactly that way?

especially the two points with the recovery and the avb_custom_key?

FP4

  1. Update the stock firmware to the latest
  2. Unlock your phone by following the instructions from Fairphone website
  3. adb reboot bootloader (or press VOLUME DOWN and plug phone while it’s shut down)
  4. fastboot flashing unlock
  5. fastboot flash recovery_a <recovery for FP4>
    fastboot flash recovery_b <recovery for FP4>
  6. In order to relock bootloader: fastboot flash avb_custom_key <avb_custom_key-FP4.bin>
  7. press POWER+VOLUME UP until reboot in recovery
  8. From recovery => Factory reset => Format Data/factory reset
  9. From recovery => Apply update => Apply from ADB => adb sideload <iodéOS for FP4>
  10. fastboot flashing lock

Sorry for not being precise, these are the steps I followed:

  1. Update the stock firmware to the latest
  2. Unlock your phone by following the instructions from Fairphone website
  3. adb reboot bootloader (or press VOLUME DOWN and plug phone while it’s shut down)
  4. (FP3) fastboot oem unlock
    (FP4) fastboot flashing unlock
  5. (FP3) fastboot flash boot [recovery for FP3(+)]
    (FP4) fastboot flash recovery [recovery for FP4]
  6. (FP4 only) In order to relock bootloader: fastboot flash avb_custom_key [avb_custom_key-FP4.bin)
  7. press POWER+VOLUME UP until reboot in recovery
  8. From recovery => Factory reset => Format Data/factory reset
  9. From recovery => Apply update => Apply from ADB => adb sideload <rom.zip> iodéOS for FP3(+) | [iodéOS for FP4]
  10. (FP3) fastboot oem lock
    (FP4) fastboot flashing lock

once again please.

You have entered the command:

fastboot flash avb_custom_key avb_custom_key-FP4.bin

was it ok? without errors? copied without errors? installation without errors?

And you used exactly that files?

  • avb_custom_key-FP4.bin
  • iode-2.3-20220126-FP4-recovery.img
  • iode-2.3-20220126-FP4.zip

Yes, I have used all those files and during the installation process no errors occured. Before the installation I verified all checksums of the files.

I have probably made some mistake during the installation, which I overlooked. I have contacted fairphone support, as I have heard, that they do fix those issues. Thanks nevertheless!

which one?

would be interesting for all of us to know to possibly avoid the same mistakes

I cannot pin point it to be honest. Everything worked fine with flashing the new ROM and Iode started normally and I could use it. Then I restarted into the bootloader and used “fastboot flash lock”, the lock screen appeared and selected lock after which the phone started into a boot loop. There I decided to turn off the phone, which might have been the wrong course of action, but I was not able to force it into the bootloader. And after switching it off, the google message “device is corrupt” appeared (as already mentioned in other posts), but also the bootloader was locked and the booting procedure only to me to the bootloader.
Hope this clarifies it further.

The last message is quite old by now, but since I had the same problem, I post my approach to fixing it:

  1. Press “Volume Down” → it then enters bootlader again
  2. Unlock bootloader again: fastboot flasing unlock
  3. Somehow, the bootloader was stuck in “a”, so I did: fastboot --set-active=b
  4. Next: Erase avb_custom_key-FP4.bin
  5. Next: fastboot flash avb_custom_key avb_custom_key-FP4.bin
  6. Next: adb sideload iode-2.4-20220407-FP4.zip
  7. Reboot and do initial set-up
  8. Update to iode 3 using OTA-updater
  9. Enable USB-Debugging
  10. Restart and enter boatloader again.
  11. Lock bootloader with fastboot flashing lock

Everything runs smoothly for me. One issue though which others might need to comment on: With every restart, there is a warning “Your device is loading a different operating system”
After a few seconds, the warning disappears and iodé boots normally.The warning does make sense given the fact that I installed a different operating system and since it runs perfectly fine, there might be no issue. But maybe someone more knowledgeable than me can comment on it?

EDIT:
a) I forgot to credit @FairphoneHulk. I used two of his posts to figure out my fix: Comment 1 and Comment 2
b) Highlighted commands for better visibility

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That’s absolutly fine and as it must
It means your bootloader is locked but not original android is running.
No need to worry

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