Trouble code u1000 on nissan titan - 2005 Nissan Titan

DTC (Diagnostic Trouble Code) U1000 is a problem with the CAN communication line.
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

This DTC sets under the following conditions:

The ECM (Engine Control Module) has lost communications with one or more of the onboard control units for a specified amount of time.

To diagnose this code you must scan all the other modules to see if they can communicate with the scanner. If all the modules are able to communicate with the scanner then the problem is intermittent and can be very hard to find. If you have one or more modules that fail to communicate then the problem is the data line to that (those) module(s).

The trouble code u referring to is a great feature here which helps in managing faults in different components of the car.