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 L-UP (Lock Up) Linear solenoid is used to control the TCC. The Transmission Control Module (TCM) monitors the Solenoid current load and resistance. If a fault is detected, the transmission will go into limp in mode, the Torque Converter Clutch (TCC) will be disabled, and the MIL will be illuminated.