Database Users

Bootloop after fingerprint sensor and ROM died

Hello,
problem above, maybe it's a hardware malfunction which would be awful.
I tried:
- whipe everything in the CyanogenRecoveryMenu
- sideload via Minimal ADB / Fastboot
- a lot more commands and helps on this site and on the internet (push,
Details:
- fingerprinter died, then the phone always crashed with blue and green flashing lights on the screen and now a bootloop
- "stock" CyanogenOS installed, but no TWRP
- the phone gets detected by my computer (sound)
- i don't remember if usb debugging is enabled (probably not)
- the command "adb devices" shows my phone when its in ADB mode (recovery menu)
- i sometimes get the error "error:closed" on my computer
Thank you for any help
doebelfish

doebelfish said:
Hello,
problem above, maybe it's a hardware malfunction which would be awful.
I tried:
- whipe everything in the CyanogenRecoveryMenu
- sideload via Minimal ADB / Fastboot
- a lot more commands and helps on this site and on the internet (push,
Details:
- fingerprinter died, then the phone always crashed with blue and green flashing lights on the screen and now a bootloop
- "stock" CyanogenOS installed, but no TWRP
- the phone gets detected by my computer (sound)
- i don't remember if usb debugging is enabled (probably not)
- the command "adb devices" shows my phone when its in ADB mode (recovery menu)
- i sometimes get the error "error:closed" on my computer
Thank you for any help
doebelfish
Click to expand...
Click to collapse
Did you also tried factory reset already?
If you have adb access you can only try to get bootloader unlocked which wipes all if not happened yet. Then you can try installing twrp and another rom and see if boot is OK.
If your bootloader is still locked go to service center if you have warranty!

strongst said:
Did you also tried factory reset already?
If you have adb access you can only try to get bootloader unlocked which wipes all if not happened yet. Then you can try installing twrp and another rom and see if boot is OK.
If your bootloader is still locked go to service center if you have warranty!
Click to expand...
Click to collapse
Thanks for a reply,
After a full reset I have downloaded a twrp.img file for my device
I tried:
- command "fastboot devices" while in fastboot-mode (I pressed reboot to bootloader in the recovery menu to get there)
-> no device detected despite a sound after connecting
- command "fastboot flash twrp.img" -> "waiting for device" without any further reaction
My device is only detected in ADB mode, not in fastboot mode, how can I change that? I must unlock the boot loader in fastboot mode right?

doebelfish said:
Thanks for a reply,
After a full reset I have downloaded a twrp.img file for my device
I tried:
- command "fastboot devices" while in fastboot-mode (I pressed reboot to bootloader in the recovery menu to get there)
-> no device detected despite a sound after connecting
- command "fastboot flash twrp.img" -> "waiting for device" without any further reaction
My device is only detected in ADB mode, not in fastboot mode, how can I change that? I must unlock the boot loader in fastboot mode right?
Click to expand...
Click to collapse
Did you have actually drivers installed for fastboot? See guides like this http://forum.xda-developers.com/zuk-z1/general/guide-how-to-unlock-root-install-twrp-t3394037
Also qfil method can help http://www.androidbrick.com/lenovo-zuk-phones-qfil-roms-unbrick-guide/
But consider service center in case of warranty.

same problem. fingerprint died. then after a empty battery shutdown i face bootloop. but hopefully i have TWRP installed and i could recover my data. but i dont know how to access factory reset menue or install another fresh rom

Stuck in Bootloop

US996 Unlocked, stock rom. I was in XDA Forums and saw there were app updates, one being Play Store. I updated. When I tried to get into Play Store, the message "this version of play store is incompatible with your device, go to settings and disable app update (or something like that). I tried but the app was not listed in settings. I tried to reboot and now the phone bootloops. All I can get is the warning that the software cannot be checked for corruption and then a quick display of the LG logo, then screen off, and then LG logo again and then warning screen, etc. If I try to reboot into recovery I get the Factory data reset screens and I answer both "yes" and the phone goes into adb mode.. From adb mode I can fastboot reboot, which puts me back into the above loop, or fastboot bootloader, which merely returns me to the adb screen. What can I do now?

Maybe try relocking the bootloader. I am pretty sure (someone correct me if I am wrong) that that pop-up of the "cannot check for corruption" usually only shows when the bootloader is unlocked.

XP_1 said:
Maybe try relocking the bootloader. I am pretty sure (someone correct me if I am wrong) that that pop-up of the "cannot check for corruption" usually only shows when the bootloader is unlocked.
Click to expand...
Click to collapse
Is that even possible? Don't know how to do it.

PhoneBull said:
Is that even possible? Don't know how to do it.
Click to expand...
Click to collapse
Try entering
Code:
fastboot oem device-info
into Fastboot on your computer to see if it says it is unlocked when in fastboot mode.

XP_1 said:
Try entering
Code:
fastboot oem device-info
into Fastboot on your computer to see if it says it is unlocked when in fastboot mode.
Click to expand...
Click to collapse
I get "FAILED (remote: unknown command)"

Do you have fastboot installed on your computer? (Something you would have had to have intentionally installed) If not google Minimal Fastboot /ADB and install it, enter the supposed ADB screen you are talking about and see if it makes contact with your phone.

XP_1 said:
Do you have fastboot installed on your computer? (Something you would have had to have intentionally installed) If not google Minimal Fastboot /ADB and install it, enter the supposed ADB screen you are talking about and see if it makes contact with your phone.
Click to expand...
Click to collapse
I have the fastboot on the PC that I used to unlock the bootloader.. I enter fastboot on the PC via the administrative command prompt. With the phone in the fastboot mode, I type "fastboot devices" on the PC and get a proper response (LGUS996ab**** fastboot). If I enter ""fastboot reboot" I get the bootloop. If I enter "fastboot bootloader" I wind up in Fastboot Mode on the phone again. I was hoping there was a "fastboot recovery" command but there doesn't seem to be. I don't know what to do next. I am not all that familiar with what can be done from fastboot. My only experience with it was when I unlocked the phone. I am desperate!

Okay, so if you do not have TWRP installed on your phone, then I don't know if you can save your data. You can try to
Code:
fastboot erase cache
and see if it helps, or if not and just reset the device fastboot oem lock I think. Maybe ask around in the unlocking help threads or perhaps someone with more knowledge will chime in. If none of this works, then there are some instructions on how to get your phone back to stock in the News and Guides section.
EDIT: Maybe try the power+volume down. It may work? I have tried it and never got it to successfully work. But you can try it.

XP_1 said:
Okay, so if you do not have TWRP installed on your phone, then I don't know if you can save your data. You can try to
Code:
fastboot erase cache
and see if it helps, or if not and just reset the device fastboot oem lock I think. Maybe ask around in the unlocking help threads or perhaps someone with more knowledge will chime in. If none of this works, then there are some instructions on how to get your phone back to stock in the News and Guides section.
Click to expand...
Click to collapse
Thanks for your help. I DO have TWRP installed and have used it often for backups. But now the only way I know to TRY to get to it is by the power/vol down until LG logo, then release/repress power button sequence but this just gets me into fastboot mode. II have some recent backups saved on my micro SD card - is there any way to flash one of them through fastboot if I load one onto the PC?

Yeah. My bad. Okay, so how I get into TWRP is through the EasyRecowvery.
Go ahead and download it from Git-Hub (1.3b3).
Now extract it and run the cmd program. Enter 5. which is extras and stuff and then enter 5 again in the sub menu which will let you boot into recovery. When you are in recovery, and plugged into your computer, you should be able to either flash or drag and drop like a flash drive on the the phone. Hope that helps a little bit.

XP_1 said:
Yeah. My bad. Okay, so how I get into TWRP is through the EasyRecowvery.
Go ahead and download it from Git-Hub (1.3b3).
Now extract it and run the cmd program. Enter 5. which is extras and stuff and then enter 5 again in the sub menu which will let you boot into recovery. When you are in recovery, and plugged into your computer, you should be able to either flash or drag and drop like a flash drive on the the phone. Hope that helps a little bit.
Click to expand...
Click to collapse
I don't have T-Mobile. I have Verizon Wireless on the US996. Will that work?

PhoneBull said:
I don't have T-Mobile. I have Verizon Wireless on the US996. Will that work?
Click to expand...
Click to collapse
Since you are only rebooting into recovery and not flashing anything it might. If not, it will just fail and not harm anything. Last thing to try is the
Code:
adb reboot recovery
which is the only thing I can think of and I think you already tried it. Otherwise you will need to just go stock.

Boot loop after Android O DP2 update

I installed Android O DP2 update via OTA yesterday. The phone updated, rebooted to the new build and restarted abruptly and since then has been stuck in a boot loop. The Google logo shows up, goes to the android animation step and then Google logo appears again.
I don't have bootloader unlocked, don't have TWRP and have done OTA updates. I am able to get into the stock recovery mode.
How do I fix this, i.e. make it work in any way without erasing the user data? I don't mind extreme steps (without erasing user data) because I was planning to reflash 7 with unlocking & rooting today.

Try to wipe cache from recovery - in recovery hold volume-down and select "Wipe cache partition". Should do the trick

I tried, didn't work. Had to factory reset in the end. Also opted out of beta

I just read that some people that took the update from certain builds had boot loops due to the update only replacing part of the OS but leaving the 7.x.x system in place causing it to boot loop. I think it was like on android authority or something like that.
Sent from my Nexus 6P using XDA-Developers Legacy app

I have similar problem. Phone became stuck at Google logo and bootloop. I didn't have OEM unlock and debugged enable when phone was working. Now I'm stuck because It cannot flash with any factory image rom. Anyone with solution, please help. Thanks

citifone said:
I have similar problem. Phone became stuck at Google logo and bootloop. I didn't have OEM unlock and debugged enable when phone was working. Now I'm stuck because It cannot flash with any factory image rom. Anyone with solution, please help. Thanks
Click to expand...
Click to collapse
You can unlock your bootloader to flash a stock ROM. Do you need the steps?
---------- Post added at 09:54 AM ---------- Previous post was at 09:38 AM ----------
citifone said:
I have similar problem. Phone became stuck at Google logo and bootloop. I didn't have OEM unlock and debugged enable when phone was working. Now I'm stuck because It cannot flash with any factory image rom. Anyone with solution, please help. Thanks
Click to expand...
Click to collapse
To flash a system image:
Download the latest system image for your Nexus 6p, then unzip it to a safe directory.
https://dl.google.com/dl/android/aosp/angler-n2g47o-factory-dc258043.zip
or Download any of your choice from here
https://developers.google.com/android/images
Connect your device to your computer over USB.
Start the device in fastboot mode with one of the following methods:
adb tool
http://developer.android.com/tools/help/adb.html
Using a key combo: Turn the device off, then turn it on and immediately hold down the relevant key combination for your device.
POWER BUTTON + VOLUME DOWN BUTTON
Click to expand...
Click to collapse
If necessary, unlock the device's bootloader using one of the following methods:
Code:
fastboot flashing unlock
If you are updating an older device, run this command:
Code:
fastboot oem unlock
The target device will show you a confirmation screen. (This erases all data on the target device.)
Open a terminal and navigate to the unzipped system image directory or Open a command prompt from within your System image folder (navigate to where you have flash-all.bat located on your PC, shift + right click anywhere within that folder, select open command prompt here
Execute the flash-all script.
Code:
fastboot flash-all.bat
This script installs the necessary bootloader, baseband firmware(s), and operating system.
Once the script finishes, your device reboots. You should now lock the bootloader for security:
Start the device in fastboot mode again, as described above.
Execute:
Code:
fastboot flashing lock
or, for older devices, run:
Code:
fastboot oem lock
Locking bootloader will wipe the data on some devices. After locking the bootloader, if you want to flash the device again, you must run fastboot oem unlock again, which will wipe the data.

Mavelos said:
You can unlock your bootloader to flash a stock ROM. Do you need the steps?
---------- Post added at 09:54 AM ---------- Previous post was at 09:38 AM ----------
To flash a system image:
Download the latest system image for your Nexus 6p, then unzip it to a safe directory.
https://dl.google.com/dl/android/aosp/angler-n2g47o-factory-dc258043.zip
or Download any of your choice from here
https://developers.google.com/android/images
Connect your device to your computer over USB.
Start the device in fastboot mode with one of the following methods:
adb tool
http://developer.android.com/tools/help/adb.html
Using a key combo: Turn the device off, then turn it on and immediately hold down the relevant key combination for your device.
If necessary, unlock the device's bootloader using one of the following methods:
Code:
fastboot flashing unlock
If you are updating an older device, run this command:
Code:
fastboot oem unlock
The target device will show you a confirmation screen. (This erases all data on the target device.)
Open a terminal and navigate to the unzipped system image directory or Open a command prompt from within your System image folder (navigate to where you have flash-all.bat located on your PC, shift + right click anywhere within that folder, select open command prompt here
Execute the flash-all script.
Code:
fastboot flash-all.bat
This script installs the necessary bootloader, baseband firmware(s), and operating system.
Once the script finishes, your device reboots. You should now lock the bootloader for security:
Start the device in fastboot mode again, as described above.
Execute:
Code:
fastboot flashing lock
or, for older devices, run:
Code:
fastboot oem lock
Locking bootloader will wipe the data on some devices. After locking the bootloader, if you want to flash the device again, you must run fastboot oem unlock again, which will wipe the data.
Click to expand...
Click to collapse
Thanks for your reply..But you can only do this only if you have an unlocked bootloader and debugged mode on. I didn't have either so it won't allow to flash with locked bootloader.

citifone said:
Thanks for your reply..But you can only do this only if you have an unlocked bootloader and debugged mode on. I didn't have either so it won't allow to flash with locked bootloader.
Click to expand...
Click to collapse
Exactly why i posted that. You can unlock your bootloader without turning USB debugging ON. Just Boot up with the POWER + VOLUME down Combination and use the bootloader unlock command in my previous post.

FAILED (remote: OEM unlock is not allowed)
Mavelos said:
Exactly why i posted that. You can unlock your bootloader without turning USB debugging ON. Just Boot up with the POWER + VOLUME down Combination and use the bootloader unlock command in my previous post.
Click to expand...
Click to collapse
What I think he is telling you and the same problem I have, when We try the unlock command we are getting this error :
FAILED (remote: OEM unlock is not allowed)
any suggestions ?
Regards.

Lord Aguacate said:
What I think he is telling you and the same problem I have, when We try the unlock command we are getting this error :
FAILED (remote: OEM unlock is not allowed)
any suggestions ?
Regards.
Click to expand...
Click to collapse
Yes, I got the same error. Again, it's because of bootloader locked and debug is off. Any other ways to unlock or flash this phone?

citifone said:
Yes, I got the same error. Again, it's because of bootloader locked and debug is off. Any other ways to unlock or flash this phone?
Click to expand...
Click to collapse
To unlock you first need to have ticked the allow OEM unlock from developer menu within the OS. It won't work otherwise.

Lord Aguacate said:
What I think he is telling you and the same problem I have, when We try the unlock command we are getting this error :
FAILED (remote: OEM unlock is not allowed)
any suggestions ?
Regards.
Click to expand...
Click to collapse
You'll have to use a Rescue OTA
Download the latest Nexus 6P OTA from here https://dl.google.com/dl/android/aosp/angler-ota-n2g47o-ec3f4df1.zip
STEPS TO FOLLOW
To apply an OTA update image:
Download the appropriate update image for your device below.
https://dl.google.com/dl/android/aosp/angler-ota-n2g47o-ec3f4df1.zip
Boot into your recovery from fastboot
use the key combination for your device
Code:
POWER + VOLUME DOWN
and then select the Recovery option from the bootloader menu. The device is now in recovery mode and an Android logo with red exclamation mark should appear on screen.
Hold the Power button and press Volume Up once, and a menu will appear. Select the option Apply update from ADB.
Run the following command on your PC:
Code:
adb devices
and check that your device shows up with "sideload" next to its name.
Run the following command:
Code:
adb sideload ota_file.zip
where ota_file.zip is the name of the file you have downloaded and verified.
Once the update finishes, reboot the phone by choosing Reboot system now.

Mavelos said:
You'll have to use a Rescue OTA
Download the latest Nexus 6P OTA from here [="https://dl.google.com/dl/android/aosp/angler-ota-n2g47o-ec3f4df1.zip"]https://dl.google.com/dl/android/aosp/angler-ota-n2g47o-ec3f4df1.zip
STEPS TO FOLLOW
To apply an OTA update image:
Download the appropriate update image for your device below.
="https://dl.google.com/dl/android/aosp/angler-ota-n2g47o-ec3f4df1.zip"]https://dl.google.com/dl/android/aosp/angler-ota-n2g47o-ec3f4df1.zip
Boot into your recovery from fastboot
use the key combination for your device
Code:
POWER + VOLUME DOWN
and then select the Recovery option from the bootloader menu. The device is now in recovery mode and an Android logo with red exclamation mark should appear on screen.
Hold the Power button and press Volume Up once, and a menu will appear. Select the option Apply update from ADB.
Run the following command on your PC:
Code:
adb devices
and check that your device shows up with "sideload" next to its name.
Run the following command:
Code:
adb sideload ota_file.zip
where ota_file.zip is the name of the file you have downloaded and verified.
Once the update finishes, reboot the phone by choosing Reboot system now.
Click to expand...
Click to collapse
Dear Mavelos,
I already tried that and the installation was successful, but my first problem still there, when I installed the Android O Beta, the touch of my screen stop working after the 2nd day of installation.
Now I don't know if this is a problem with Android O or just a coincidence and the hardware its broken.
I went to a lot of forums but nobody its talking about that (Touch Screen not working)
Did You guys hear anything about it?

Mavelos said:
You'll have to use a Rescue OTA
Download the latest Nexus 6P OTA from here https://dl.google.com/dl/android/aosp/angler-ota-n2g47o-ec3f4df1.zip
STEPS TO FOLLOW
To apply an OTA update image:
Download the appropriate update image for your device below.
https://dl.google.com/dl/android/aosp/angler-ota-n2g47o-ec3f4df1.zip
Boot into your recovery from fastboot
use the key combination for your device
Code:
POWER + VOLUME DOWN
and then select the Recovery option from the bootloader menu. The device is now in recovery mode and an Android logo with red exclamation mark should appear on screen.
Hold the Power button and press Volume Up once, and a menu will appear. Select the option Apply update from ADB.
Run the following command on your PC:
Code:
adb devices
and check that your device shows up with "sideload" next to its name.
Run the following command:
Code:
adb sideload ota_file.zip
where ota_file.zip is the name of the file you have downloaded and verified.
Once the update finishes, reboot the phone by choosing Reboot system now.
Click to expand...
Click to collapse
I have the same problem as others, stuck in a bootloop and had not enabled unlock in dev options. I can get to bootloader but not recovery mode (bootloops when I select this). I would love to try this OTA side load, but I can't see my device in adb. I can see it however in fastboot. Not sure how to get it up in adb....
Any help would be much appreciated.

scorneil said:
I have the same problem as others, stuck in a bootloop and had not enabled unlock in dev options. I can get to bootloader but not recovery mode (bootloops when I select this). I would love to try this OTA side load, but I can't see my device in adb. I can see it however in fastboot. Not sure how to get it up in adb....
Any help would be much appreciated.
Click to expand...
Click to collapse
If you get a bootloop when selecting recovery, try rebooting to recovery with fastboot
Code:
fastboot reboot recovery
if that doesn't work, then i think your device is bricked.
---------- Post added at 06:19 AM ---------- Previous post was at 06:16 AM ----------
Lord Aguacate said:
Dear Mavelos,
I already tried that and the installation was successful, but my first problem still there, when I installed the Android O Beta, the touch of my screen stop working after the 2nd day of installation.
Now I don't know if this is a problem with Android O or just a coincidence and the hardware its broken.
I went to a lot of forums but nobody its talking about that (Touch Screen not working)
Did You guys hear anything about it?
Click to expand...
Click to collapse
If your touch screen isn't working, it might be related to the Android O Beta you flashed. Can you boot the phone up? If you have an OTG cable, connect a mouse to your phone. Turn on OEM unlocking in developer options. Do a factory reset.

i have the same problem with this, and i cannot unlock it too, is there anyway to unlock this phone?

OTG works Perfect! But.....
Mavelos said:
If you get a bootloop when selecting recovery, try rebooting to recovery with fastboot
Code:
fastboot reboot recovery
if that doesn't work, then i think your device is bricked.
---------- Post added at 06:19 AM ---------- Previous post was at 06:16 AM ----------
If your touch screen isn't working, it might be related to the Android O Beta you flashed. Can you boot the phone up? If you have an OTG cable, connect a mouse to your phone. Turn on OEM unlocking in developer options. Do a factory reset.
Click to expand...
Click to collapse
So I Follow your suggestion and I bought the OTG adapter, works perfectly I unlocked the bootloader from the developers options, did a factory restore with a previous image, etc.... Touch still not working, I'm starting to believe this a hardware problem with the screen.... Bad Luck maybe, I don't know! ..... I will have to buy that expensive screen ($140).
Anyway thanks for the help...
Regards

Lord Aguacate said:
So I Follow your suggestion and I bought the OTG adapter, works perfectly I unlocked the bootloader from the developers options, did a factory restore with a previous image, etc.... Touch still not working, I'm starting to believe this a hardware problem with the screen.... Bad Luck maybe, I don't know! ..... I will have to buy that expensive screen ($140).
Anyway thanks for the help...
Regards
Click to expand...
Click to collapse
You're welcome. Get your phone fixed and return to the flashing community.

last night i my phone inside my freezer hehehe and this morning i tried to turn it on, and it pass the google logo boot normally but it only lasted for a few minute and then turn off and bootloop again. so i guess my 6p has a hardware faulty

re-locking boot loader & restore

How can I relock the boot loader and restore my Stylo 2 to factory default? Provider is T-mobile.

fastboot flash oem lock.
Note however if you used twrp this will brick your device unless you flash the original recovery first. Provided you got the kdz or LG bridge you should be able to just lock put in download mode and use the repair recovery option.I'm not responsible if you brick your device. Good luck

Frosthaxx said:
fastboot flash oem lock.
Note however if you used twrp this will brick your device unless you flash the original recovery first. Provided you got the kdz or LG bridge you should be able to just lock put in download mode and use the repair recovery option.I'm not responsible if you brick your device. Good luck
Click to expand...
Click to collapse
I had used LG Bridge to reflash my phone so I believe that I have original recovery on the phone. How can I verify?

When I enter fastboot flash oem lock I get < waiting for device> on my terminal screen and thats it?

Once you have the phone wiped completely back to default (including recovery) with the LG tools. Enable developer mode, and then enable USB debugging. While it is plugged into your PC navigate to the folder where you have the ADB applications in CMD or add the location to your Environment variables. The latter will allow you to launch ADB/fastboot commands from any location in CMD. I definitely suggest this. With your phone connected run "adb devices" to make sure that it sees your device. Then run "adb reboot-bootloader" to reboot into the bootloader. While on that screen run the command "fastboot flashing lock_critical". It should prompt OKAY then give the time it took and also that all of the user data was deleted. Then finish up by typing "fastboot reboot". That will put the phone back into a normal mode. Boom, you are done.

Help
When I use the fastboot oem lock, at the moment when I power on the phone in the screen appears the text "Your device has failed a routine safety check and will not boot.
This may be a temporary problem.If this message occurs rerepeatedly, visit this link on another device and refer to the Red case: g.co/ABH
I have two days looking for the solution, and I didn't found anything

Back to stock, relock bootloader problem waiting for device

Hi,
i used Miflash in edl mode to get back to stock rom. after flash and reboot I used the recovery mode to do a factory reset.
It seems to work. It shows Android Recovery, but the bootloader is still unlocked.
What mode do I need to enter to use the "fastboot oem lock" command? I always see "waiting for device" and nothing happens
When I type "adb devices" I can see the phone. I saw there is a command "fastboot devices", too. but it shows me no result.

Stevie123 said:
Hi,
i used Miflash in edl mode to get back to stock rom. after flash and reboot I used the recovery mode to do a factory reset.
It seems to work. It shows Android Recovery, but the bootloader is still unlocked.
What mode do I need to enter to use the "fastboot oem lock" command? I always see "waiting for device" and nothing happens
When I type "adb devices" I can see the phone. I saw there is a command "fastboot devices", too. but it shows me no result.
Click to expand...
Click to collapse
Reboot to fastboot using
adb reboot fastboot
Click to expand...
Click to collapse
Then, try to use fastboot cmd

Thanks, before I can try that I have to solve another problem.

That doesn't work. The phone isn't entering a special mode. I can choose fastboot from the bootmenu, too. But nothing happens. The phone does a restart, shows the bootmenu again and boots android after 5 seconds.

@Stevie123
You need to enable fastboot (bootloader) mode since it is disabled by ZTE, so that the selection from menu to be effective (after enabling it, in fastboot mode, your command "fastboot devices" (to check) and "fastboot oem lock" (to lock bootloader) will be accepted).
You can use Axon 7 EDL tool to unlock the bootloader.

It's already unlocked. I have to make another unlock procedure again to get access to fastboot? The EDL Tool tells me that I have to wipe and reset the phone after it. So it seems I can't keep my data and just lock the bootloader.

Either Lock or Unlock will wipe your data. And yes, the unlock procedure by Axon 7 EDL tool includes the enabling of fastboot. So you have to re-unlock if you want to relock.

I think this EDL tool doesn't work very good. It flashed something to make fastboot available, but I had a green ZTE Logo screen and this screen also had errors like white spots. The original ZTE logo is in cyan. But the fastboot worked and I could lock the phone. But I couldn't do anything else anymore. I couldn't reach Android and reflashing also didn't work. So I tried to use the EDL Tool to unlock my bootloader again. It said success, but it didn't work. It was still locked.
Well, I had to wait until the phone was empty. Luckily I could reach EDL Mode again. I used the MiFlash again to Downgrade to Android Nougat B12. I read somewhere that the fastboot is included there. So I had the right ZTE Logo back and it worked. I could leave the Bootloader locked. The final update I did with a SD Card to the lastest Android Software for Axon 7. Luckily without a brick. It's a pity that they don't offer any Updates anymore.