Galaxy S4 not connecting via phone bluetooth

[AC Question]

About 3 weeks ago, my otherwise perfectly working S4 lost the phone Bluetooth function on all headsets and car systems. It still pairs and connects just fine, and transmits music via the A2DP system to the Bluetooth devices. However, when I make or receive a phone call, the phone call does not get transmitted (neither my voice nor the other side's voice).
I have spent several hours on the phone with ATT tech support. They were stumped, as were the folks in the store and the Samsung rep at our local Best Buy store.
A hardware factory reset did nothing, nor did updating all apps. OS is latest available: 5.0.1. Installing SoundAbout, suggested by some on this forum, also did not fix this. I took it to a local repair shop where they ensured that the antenna was connected (they had recently replaced the power switch and I had suspected that they might have inadvertently disconnected the antenna - but apparently not). The repair shop believes it's a software problem. I suspect the same, but need ideas on what to check.

 

[B. Diddy]

Welcome to Android Central! You've probably checked this already, but when you connect to the Bluetooth device, go to Settings>Bluetooth​, tap the device, and make sure Phone Audio is checked on.

 

[HolgerC]

Yes, that was one of the first things I checked.

 

[B. Diddy]

Did you also completely forget the pairing in the car and other Bluetooth devices, then go through the whole pairing process again?

How about trying to pair in Safe Mode?

 

[HolgerC]

After the factory reset, all my BT devices needed to be paired again, but that did not change anything. At one time, I did start the phone in Safe Mode, which then again did not make a difference in the BT functionality. I have not actually gone through the process of forgetting the devices, then pairing in Safe Mode. Could try that, I guess.

 

[B. Diddy]

Did this start after a system update? You might try reinstalling the firmware using either Samsung Kies or Smart Switch. If neither of those work, try reflashing the firmware using Odin: http://forums.androidcentral.com/am...w-flash-stock-rom-via-odin-new-interface.html

 

[HolgerC]

Interesting you might suggest that. The Samsung rep told me that flashing would be doing less than the factory reset did - which produced no change. I truly don't know enough about it to have an opinion on whether that might work. I also see on the site you suggest that there were several entries by people stating that the process did not work for them and left their devices useless.
At this point I am contemplating buying another S$ with a broken screen, and swapping out the insides so that I have at least one functioning phone. That option might take care of software, firmware and hardware issues..

 

[B. Diddy]

I'm not sure why the Samsung rep would say that. If the firmware is corrupt, doing a factory reset won't do anything to fix that, since it's still the same firmware on the phone. Reflashing the firmware can potentially fix that problem. I've seen many people attest to this on these and other forums.

But flashing firmware via Odin requires that you select the exactly correct firmware for the device--flashing the firmware for a different model (and this could be a different regional variant of the same phone) can cause problems. So that might be one of the reasons why some people run into problems.

 

[Golfdriver97]

Did this happen after an update? The update may not have properly installed and reflashing the ROM may help. Keep in mind that it may be an issue with that version of the software. What was given via OTA may be the exact same as reflashing via Odin.