No Sound issue on Moto G4 (Amazon edition)

[Android Central Question]

Hi!
My phone is a Moto G4 running Nougat. For the last few hours, I've been having an issue with the sound. I can't get the speakers or any plug-in earbuds to play any sound. I've checked that the system sound is not muted, and the earbuds I'm using work fine with other devices. There's neither message tone nor app sound despite both of those channels being non-zero (I've tried different levels).
Further, there is some odd behavior. Video will not record, though photos are fine. Whenever I try to play music, both players I've tried (Google Play Music and Musicolet) simply skip from track to track, even though I'm either trying to play files I'm sure are on my phone, or using the Google Play radio function. Several other apps that require sound crash before loading.
Finally, some of these issues stop when the phone is paired with a bluetooth audio device. This is the case both with a pair of bluetooth headphones and with my car's bluetooth stereo. If I'm paired with bluetooth audio, I can listen to music and apps with sound stop crashing. However, I'm still unable to record video.
Any idea what might be wrong, or what I can try? I've tried a factory reset to no avail, and there aren't any system updates available. Thanks very much in advance!

More phone specs:
Chipset Qualcomm Snapdragon 617 MSM8952
Graphics Adreno 405
Processor Octa core, 1.5 GHz, Cortex A53
Ram 2 GB
Android 7.0

 

[B. Diddy]

Welcome to Android Central! Does it also happen in Safe Mode? https://motorola-global-portal.custhelp.com/app/answers/indevice_detail/a_id/111313/p/30,6720,9686

 

[artrexdenthur]

Thanks very much for the reply! I couldn't figure out how to do safe mode before so I hadn't tried that.
But yes, exact same issues persist in safe mode.

 

[B. Diddy]

I'm guessing that the firmware got corrupted somehow. Factory reset wouldn't fix that, since it's using that corrupt copy of the firmware. You could try reinstalling the firmware -- here are a couple of guides:

https://www.techdroider.com/2016/05/guide-how-to-install-stock-firmware-on-moto-g4-4th-gen.html
https://www.thecustomdroid.com/restore-stock-firmware-on-moto-devices/

 

[artrexdenthur]

Yeah, that would be the next step. Unfortunately, I went for the cheapskate option and this is the Amazon Prime Exclusive version which is ineligible for bootloader unlocking (I tried going through the process just the other day on Motorola's site to make sure, since they did remove the lockscreen ads, but still no dice).
I did try the flash just now, following the Techdroider. Every flash line except for flash modem and flash fsg that tried to run gave the error "Invalid signed image," which I read is associated with a locked bootloader.
So the result of flashing modem and fsq, along with erasing, seems mostly to be that the phone seems mostly just to be factory reset again.

HOWEVER

I pulled up Google Play Music and the speakers worked. I then attempted a phone call, BUT on neither end could I hear anything out of the other's microphone. I then dowloaded a voice recorder, which showed sound being recorded but could not play it back on the onboard speakers. I then tried each of these things again with an earbud headset, and everything seems to work fine from the earbuds and their microphone, including phone calls. This had previously only worked with bluetooth devices, and even then I could not talk/hear with phone calls.

So now the usability/app crash issues I was having seem to have gone away, leaving the only issue being the onboard speakers not working, and the microphone not working for calls. I did double-check at various points that this is not an issue of the volume being turned down.

Any further thoughts? My feeling is that, given the inconsistent behavior of the microphone (functions for the recorder but not the phone) that this still might be a software issue. Does this make sense? If so, do you know of any way to force the bootloader to unlock, or to make the flash work without an unlocked bootloader? I'm still working under the assumption that the flash failures were the locked bootloader's fault.

Thanks again!

 

[B. Diddy]

From what you're describing, I agree -- it does sound like a software/firmware issue. But that gets us back to the problem of how to reinstall the firmware, since as we discussed above, a factory reset will just use the same corrupt firmware. Unfortunately, I don't have any real experience with this kind of in-depth tinkering with a phone. I'll see if any of the other Ambassadors or Mods have an idea. It also might be worth posting your question at the xda-developers.com forums, since they tend to be more technical.

On other small thing to try -- see what happens if you uninstall updates to Chrome. Sometimes, updates to Android System Webview can cause glitches with certain devices, and in Nougat and above, Android System Webview is handled by Chrome.