Hello!
My car has an original firmware Z120BT to which an old iPhone was paired and working. I upgraded to a newer phone and am trying to pair again as per the Z120's quick start guide but it's just not happening. The phone sees the PIONEER-NAVI as something to pair to, but when I try it fails. The Z120 will eventually say registration failed and Bluetooth is then off until I restart the car.
Assuming it's just crappy decade old firmware I looked through the updates on the Pioneer USA site and the most recent I can find for the Z120BT is 2.003 which doesn't appear to be any newer.