Bluetooth audio codec missing?

I've now unpaired the headphones and performed an SMC reset, but unfortunately I'm still getting the same behaviour as before.

Below is the Bluetooth Explorer Event Log; the headphones automatically disconnect approximately 15 seconds after connecting. It is during these 15 seconds that "Active Codec: Not active" shows up in the Bluetooth context menu and the headphones are listed in System Preferences -> Sound -> Output.

My initial guess was that the disconnecting is just a consequence of an underlying problem that also causes the inability to play sound through the headphones, but I'm not sure.

I'm having the same problem with Bose QC 35 headphones and a MacBook Air (Early 2015, macOS Sierra 10.12.6). Anyone knows what "Active Coded: Not active" means?

The headphones do show up as an output device in System Preferences -> Sound.

Music does not play through the headphones, however, and the headphones disconnect automatically after 10 seconds.

Can you please clarify what you mean by playing a test sound? I can't find a test sound option in System Preferences -> Sound. I wanted to try playing the test sound through the Audio MIDI Setup built-in utility, but the headphones do not show up in the device list there (even though they do show up in System Preferences -> Sound -> Output).

Yes, thanks. When clicking the speaker icon on the Sound Effects tab, the test sound plays through the internal speakers, even though "Selected sound output device" is chosen in the "Play sound effects through" combo box, and I had selected Bose QC35 II as the sound output device on the Output tab. There is no option to select the Bose QC35 II headphones directly in the "Play sound effects through" combo box on the Sound Effects tab.

No, I've unpaired the headphones from all other devices and cleared their own device list, in order to debug connecting to the MacBook Air in isolation.

Yes, the QC35 headphones are supposed to have NFC as well, but I've never used it.

Un-pair the QC35. Run a SMC reset - How to reset the System Management Controller (SMC) on your Mac - Apple Support - pair the QC35 and test.

Daresay you've solved this now, but – daft as it might sound – have you tried playing music (via iTunes, Spotify, whatever) and then repeating the exercise with the music playing?

After the device has been paired, do you see it as an output (or input) device in System Preferences -> Sound?

The device is paired but is not an active destination for the output stream. What is the source of Music when you test them? Can you hear the music on internal speakers?

Thanks for your response. I tried playing the music from both VLC and Google Chrome, and in both cases it continues to play on the internal speakers.

Without any of the sources, if you play a test sound, does the QC35 play any sounds when set as the output?

Do you have a Sound Effects tab in System Preferences -> Sound?

Is the QC35 paired to more than one other device? Does your QC35 have NFC and BT, both?

Do you have another BT headphone with which you can test the Mac side? If you have a Windows PC, can you try pairing the QC35 to that and see if it needs additional drivers.