Theory Of Operation
WARNING: This page is about a different car, the 2015 Fiat 500. However, it is still accessible from the selected car via links, so may be relevant.
The Powertrain Control Module (PCM) stores a copy of the vehicle's module build configuration in its EEPROM. If the stored information in the PCM does not match the information sent over by the BCM of what modules are active on the CAN Bus, the DTC will set.