I have an AVH4400NEX that has suffered the boot loop/failed internal SD card issue. 

After a few hundred power cycles, these units will clear the boot loop and go into a mostly functional state. Wireless CarPlay won’t work, and the USB database has to be built every time it’s connected or power cycled. 
 

Without doing any research, I tried updating from 1.0 to 1.02 to see if that would help. The update failed after a few dozen looped attempts. 

I read about the SD card fix here:

Unfortunately, upon doing this it goes back to the update screen, and instead of saying “updating 1.0——1.02” it says “updating 0.0——0.0,” which is the same behavior as having no USB plugged during the update screen. 
 

If I replace the original SD card, and plug the update USB back in, it will go back to the original “update failed” loop. 
 

I direly need some help. I’ve burned 2 SD cards and still am stuck with a disassembled pile of Pioneer. I have a spare and can get more if needed, but I’d like the third time to be a charm. 
 

Thanks in advance! 

This is just my experience with a 4500. I tried putting the image on an SD card using windows and it failed, the unit still didn’t work. Then I used a Linux machine to put the image on a card and it worked. I believe there is a 4400 file here somewhere. If you have it then try using a different image burner, or like I did a Linux machine. 
Just my experience.