Possible causes

– Controller Area Network (CAN) communication harness is open or shorted
– Faulty Engine Control Module (ECM)
– Poor harness ground connection.

Tech notes

Usually the problem is poor harness ground connection.

There is a service bulletin for the following Nissan models with U1000 code:

2002-2006 Nissan Maxima
2004-2006 Nissan Titan
2004-2006 Nissan Armada
2002-2006 Nissan Sentra
2005-2006 Nissan Frontier
2002-2006 Nissan Altima
2005-2006 Nissan Xterra
2005-2006 Nissan Pathfinder
2004-2006 Nissan Quest
2003-2006 Nissan 350Z
2003-2006 Nissan Murano
Nissan Factory Service Bulletin Code U1000

The service bulletin suggest cleaning engine and body harness ground connection to repair problem.

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)

U1000 NISSAN Description

Controller Area Network (CAN) 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.

NISSAN Technical Service Bulletins for U1000 code