With current pfSense 2.3.2 and APU2C4 it's not possible to read the CPU temperature of. The problem isn't new but it's not solved in official images.

I found a solution for the problem in this forum (Thanks to Stephan).

It wasn't tricky, but if you want the short story:

1. Download the changed kernel module
2. Extract the archive and copy the amdtemp.ko file to your box, to /root
3. Execute following commands:
   kldunload amdtemp
   cp /root/amdtemp.ko /boot/kernel/
   kldload /boot/kernel/amdtemp.ko

After this steps, you'll see the current temperature in the Dashboard view.