In vehicles equipped with control modules, a communication protocol known as CAN bus (Control Area Network) is implemented. It is through this circuit that the controllers are able to communicate and send operating information from the different systems of the car. For the CAN bus, there are two wires known as CAN high and CAN low, through which the data transmission process is carried out.
When the Control Area Network is not working, its two lines have 2.5V but when data transmission begins, the high line becomes 3.75V and the low line drops to 1.25V. Between the two lines, a difference of 2.5V is maintained, which results in avoiding problems for the CAN bus from electric fields or noise.
The establishment of fault code U0426 OBDII occurs when it is detected that the Vehicle Immobilizer Control Module has presented problems when communicating with another controller through the CAN bus, sending information considered invalid.