FP4 bootloop after Android 15 update (SREL 15.14.4) — Android 13 factory boots fine

Help Fairphone 4
,
1

I hit a reproducible bootloop on my Fairphone 4 after trying the new Android 15 update. The phone shows the Fairphone boot animation (the “I ⇄ Fairphone” logo), hangs ~30 seconds, then restarts, repeat forever. It never reaches the setup wizard.

Device

  • Fairphone 4 (FP4), model: F4FPHN-1DG-EU1

  • Before this: no modding at all (no root, no custom ROM, no system/fastboot usage). Only stock Fairphone OS + normal OTA updates.

Build that fails

  • FP4.SREL.15.14.4.20251229152255.user-factory.zip

What I tried (all with no flashing errors)

  1. Correct Windows USB/fastboot driver

  2. Bootloader unlocked + unlock_critical (wiped data)

  3. Factory reset / wipe data

  4. Switched slot a/b (no effect)

  5. Recovery wipe (menu accessed via Power + VolUp from “No command”)

  6. Reflashed the Android 15 factory image multiple times

  7. fastboot erase avb_custom_key (OKAY), then reflashed again

  8. Still bootloop on Android 15

Result / workaround

  • Flashed the Android 13 factory image → boots flawlessly and is usable.
    So for me it’s clearly A15-specific (not a general “bad flash” situation).

Fastboot snippet

  • product: FP4

  • unlocked: yes

  • current-slot: a

  • slot-successful:a:no and slot-successful:b:no (never becomes successful on A15)

  • Full fastboot getvar all available if anyone wants it.

Extra note
This started right when the Android 15 update launched and I first tried to install it in-place (OTA) from Android 13. After that, A15 won’t boot even after clean factory flashing.

If anyone else with FP4 sees the same “I/Fairphone logo → reboot” loop on SREL 15.14.4, would be good to compare variants and see if Fairphone acknowledges it / has a fixed build coming.

2

what OS/version was installed when you updated to 15.14.4? Is your fingerprint reader working?Did you try to install the first A15 version or did you skip it and 15.14.4 was your first attempt?

3

  1. finger print reader is disabled / i don’t use it. Should i check? If yes, how? just activate and see if it can unlock my device with it? Can a faulty reader mess up security checksum or something similar leading to this?

  2. First time when it failed inplace was with the first version of Android15 somewhen in 11/2025 i guess: Android13 (FP4.TP31.C.0143) → Android15 (FP4.QREL.15.14.3)
    As device then reverted to Android13 after failed upgrade, i ignored it. Only when i had time (the last days) i tried all the steps i described above to come clean.
    This time: Android13 (FP4.TP31.C.0143) → Android15 (FP4.SREL.15.14.4)
    I though there might be deeper issues with the OS, as i only did inplace upgrades since purchase in 2021.

4

Yes its worth a try to check the fingerprint is working.

You could try this

touch the fingerprint sensor with a slightly wet finger during boot.

Or when it boots with A13 (not sure what your current status is) set-up fingerprint and/or use the internal tests…

1 Like
5

Setting up fingerprint isn’t available in menu.
Sensor self test & board test via internal tests (*# *#2886*# *#) are failing
I guess with some warranty left, I´ll contact Fairphone!
Thanks a lot for your help!

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