If your car is displaying this U0100 error code in your OBD scanner, then there is a communication problem within the vehicle's network, CAN Bus:
It is usually displayed as U0100 error. Description: Lost Communication with ECM/PCM "A"
Related Systems: Network Communication.
The Controller Area Network also called CAN bus, is the communication network that links all the control units and modules in your car including the E-C-U's and the PCM.
The E-C-U or ECM is the major part of the brain behind the engine operation, SRS, ABS, body chassis, and even PCM. While the PCM on the other hand, is the brain behind the trasmission functions and all the sensors there in.
The CAN Bus is a two-wire system; CAN-High and CAN-Low that allows data to be transmitted between E-C-U's. The CAN bus is used for real-time communication and plays a key role in ensuring the various systems work together harmoniously.
This error code issues could be likened to neurological problem in human.
And just the as man will suffer severe seizure and spasm when suffering a neurological problem, same way your car will suffer jerking, stalling and all the seizure like issues when having this problem.
When this code appears, it usually means that there's a breakdown in communication between the various E-C-U's and the CAN bus. The specific issues that can trigger a U0100 error code includes all that is discussed in this video.