[CplJonlan]

Thanks, that did it. I got 3913 as a temperature for -18.3 degrees Celsius. When converted to hexadecimal, that's 0x0f49 and when sign-extended to integer it's 0xff49 ie. -0x00b7 which is -183 in decimal.

I put my findings here with some extra notes in case someone wants to use the sensor modules in their project.