The CAN bus (Control Area Network) is a serial communication line or network for vehicles in real-time. Data regarding vehicle operation is transmitted through this communication network at the right speed. Take into account this network has a high error detection capacity.
The control modules installed in the vehicle share information with each other, and link with other control units during operation time. During the information exchange, the units are connected with 2 communication lines. The CAN H line and CAN L line allow a high speed of information transmission with a smaller number of cables. Although each unit transmits and receives data, it uses a required selection process to read the data.
When the U1001 OBDII fault code is set, it is because the ECM (Engine Control Module) is not receiving or transmitting the OBDII communication signal related to the emission system for more than 2 seconds.