Bluetooth not available: Mojave 10.14.2
It may be necessary for the Bluetooth demon to be stopped when deleting the file. Here's what worked for me (some of this may be unnecessary or redundant):


Turn off bluetooth, e.g. from the toolbar icon.
Run this command (you'll probably be prompted for your password):

sudo pkill bluetoothd \
    &amp;&amp; sudo rm /Library/Preferences/com.apple.Bluetooth.plist \
    &amp;&amp; sudo pkill bluetoothd

Go to the Bluetooth System Preferences pane and click the "Show bluetooth in menu bar" checkbox twice (to remove and then re-show it).
In the Bluetooth System Preferences pane, delete the device you want to connect to.
Turn on bluetooth.
Turn that device on and in pairing mode.
Pair with it.


It was not necessary for me to do anything with the SMC or NVRAM, or restart the machine.