How to select Hands-Free Profile (HFP) mic?

So, I have an app which, when connected to car's HFP, needs to use the car's mic. It works fine without BT, it works fine with a BT headset, but not with HFP - when it is connected to my car's BT it uses HFP speakers but not the mic.

What am I doing wrong? Is it an Android bug?

private static boolean isBluetoothHeadsetConnected() {
    BluetoothAdapter mBluetoothAdapter = 
    BluetoothAdapter.getDefaultAdapter();
    return mBluetoothAdapter != null && mBluetoothAdapter.isEnabled()
        && 
    mBluetoothAdapter.getProfileConnectionState(BluetoothHeadset.HEADSET) == 
    BluetoothHeadset.STATE_CONNECTED;
}

private boolean checkBlueTooth()  {
    if (!isBluetoothHeadsetConnected()) {
    return false;
    }

    return true;
}

private void useBluetooth() {
    AudioManager audioManager;
    audioManager = (AudioManager) getSystemService(AUDIO_SERVICE);
    audioManager.setMode(AudioManager.MODE_IN_COMMUNICATION);
    audioManager.startBluetoothSco();
    audioManager.setBluetoothScoOn(true);
}

protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    if (checkBlueTooth()) {
    start();
    } else {
    BroadcastReceiver scoReceiver = new BroadcastReceiver() {
        @Override
        public void onReceive(Context context, Intent intent) {
        if (intent.getIntExtra(AudioManager.EXTRA_SCO_AUDIO_STATE, -1) ==
            AudioManager.SCO_AUDIO_STATE_CONNECTED) {
            start();
        }
        }
    };
    IntentFilter intentFilter = new IntentFilter();
    intentFilter.addAction(AudioManager.ACTION_SCO_AUDIO_STATE_UPDATED);

    this.registerReceiver(scoReceiver, intentFilter);
    useBluetooth();
    }
}