To enable & disable Bluetooth using below adb commands needs your device to be rooted or if you are working on android development, your android should be userdebug build with root access.,
Enable Bluetooth
$ adb shell service call bluetooth_manager 6
Disabled Bluetooth
$ adb shell service call bluetooth_manager 8
Open Bluetooth Settings
$ adb shell am start -a android.settings.BLUETOOTH_SETTINGS
If you are using only user build during development or you don’t have root access, you can still enable bluetooth as mentioned in our another post “adb shell command to Turn ON Bluetooth & make it discoverable”