This is a manufacturer specific network code. Specific troubleshooting steps will vary depending on the vehicle. The trouble code U1000 is a vehicle specific code primarily found on Chevrolet, GMC and Nissan vehicles. It refers to a Class 2 communications failure..Generally, this code will precede an additional code that identifies the module or area of the failure.The second code may be generic or vehicle specific.The electronic control unit (ECU) which is the primary computer on the vehicle is unable to communicate with a module or a series of modules.enerally, this code will precede an additional code that identifies the module or area of the failure. The second code may be generic or vehicle specific. The electronic control unit (ECU) which is the primary computer on the vehicle is unable to communicate with a module or a series of modules.