Very bad sign. so Modem Firmware is located on BB_CPU and if you are not getting the firmware its a few of the following that can affect this
# BB_PMU is not working right therefore you may not be getting voltage to power the BB_CPU
# There is a issue with WTR and it is messing with the voltages of PMU
# BB_CPU needs reballed due to corrosion
# BB_CPU has a internal short
Either way this is a Motherboard that will need a Microsoldering Tech to repair.