Possible causes

– Harness or connectors (CAN communication line is open or shorted)
– ECM

Tech notes

Nissan has release service bulletins for this problem. A common cause with Nissan vehicles is the poor harness ground connection at the engine compartment and the ground connection behind the dash. Clean and resecure harness ground connection and reset engine light.

When is the code detected?

When ECM is not transmitting or receiving CAN communication signal of OBD (emission related diagnosis) for 2 seconds or more.

Symptoms

– Engine Light ON (or Service Engine Soon Warning Light)

U1001 NISSAN Description

CAN (Controller Area Network) is a serial communication line for real time application. It is an on-vehicle multiplex communication line with high data communication speed and excellent error detection ability. Many electronic control units are equipped onto a vehicle, and each control unit shares information and links with other control units during operation (not independent). In CAN communication, control units are connected with 2 communication lines (CAN H line, CAN L line) allowing a high rate of information transmission with less wiring.
Each control unit transmits/receives data but selectively reads required data only.