For reference, I thought I would share my experience of upgrading my modem on my 2016 Ford Fusion Energi. To start off, I think if you have done the Sync 3 upgrade, you should be able to do the 4G upgrade. They are of similar difficulty and not very hard to do at all if you follow the steps.
I initially installed the HJ5T-14G087-UF variant of the 4G modem. Upon installation it provided a DTC of U3000:04-0A. This is an internal code described as "System Internal Failures". I attempted to reset the modem as well as flashing the firmware to the newer version -UM firmware. This did not solve the problem. The modem would not work and never showed a signal or anything indicative of it being operational. This something that is not super common, but it does happen (as seen on the f150forum).
Luckily, I had bought a second one (also HJ5T-14G087-UF) as it was only $50 on eBay. I installed this modem and it worked perfectly. Right away it showed as being ready for authorization. I changed the first two blocks to the appropriate values for my vehicle. Then I began flashing the -UM firmware. It took just under an hour to complete and I was able to finish on the first attempt. I did this with the OBDLink EX connected through a USB 2.0 hub. I also had an 8 amp charger hooked up to the 12v battery, though it is listed that the charger should be 6 amps at minimum. After the firmware was flashed, I attempted the activation process on the FordPass app but since the app is somewhat buggy, I used the ConnectedCar site to start the activation. This seemed to get everything in order and the app started treating my vehicle properly. Almost instantly, I was able to use remote start, lock/unlock, and view charging status. While the connection seemed to stutter at first, with FordPass only receiving "partial data", everything got better over a couple hours. I still am unable to toggle the charge status notification. I am presented with a long loading screen until it eventually times out. I will wait a couple more days to see if anything changes.
