Chosen Solution
Eek! A few weeks ago (right after I discovered the data-& energy-saving “tether via bluetooth” function on android, sigh..) I found that my MBP showed me the “bluetooth unavailable” symbol in the icon bar: A greyed out icon with a sawtooth wave on front of it. I could not connect to any device, no submenu is shown. But: this does occur randomly! So I guess this is some hardware defect? Additionaly, recently when I opened the MBP, the screen would flicker initially (not the green-stripe flicker, but some flashing, then grey/white noise, then the standard screen, with the “BT not available” symbol. Is the BT antenna somewhat connected to the screen cable? Is there something I can do to fix the BT issue and to prevent things getting worse?
Bluetooth and screen cables share the same pathway where the LVDS display cable as well as the Bluetooth/WiFi antenna cables pass on their way to the lid assembly. Your issue might indicate the plastic clutch cover has been bumped at some point and/or cables inside might have been partly damaged or dislodged. Check the clutch cover for signs of impact. You might just have to replace the cables as well. Review this IFIXIT guide MacBook Pro 15" Unibody Mid 2012 Display Replacement
