I downloaded the 5.1 firmware from pioneer's website (currently, I have 4.6) and tried to update the unit following the instruction, the update went through and shows complete, but the unit didn't do automatic reboot, so I manually restarted the car, when in program force write, it does show the ucom version of 8.5, however, in system setting, the app version is still 4.6.  Do I need special tool to be able to update to 5.1 firmware?

Thanks!

I didn't do the 5.1 update but had the same issue with 4.6. I had to disconnect my batteries in order to remove the card. I removed the firmware update from the folder so it was by itself on the card Installed once more repeated the battery step removed card and restarted the system, and it updated itself and rebooted

The same thing happened to me doing the 4.6 update installed using a USB flash drive. It didn't automatically reboot (although stated complete). None of the buttons on the unit worked. I unplugged the USB drive, nothing happened. I shut off my car, nothing happened (the unit stayed on and was basically frozen). I had to unplug my car battery, wait 5 minutes then turned my car back on. The HU started normally again but the version still states its 4.0.

Thanks for the tip from Clandest1ne.. I will try it again but next time i'll use an SD card.