U1000 – CAN communication line – signal malfunction (Nissan)

Reinier

By Reinier (Contact Me)
Last Updated 2018-07-09
Automobile Repair Shop Owner

Trouble CodeFault LocationProbable Cause
U1000 CAN communication line – signal malfunction Wiring

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What Does Code U1000 Mean?

OBD II fault code U1000 is a manufacturer specific code that is defined by carmaker Nissan as “CAN Communication Line – Signal Malfunction”*, and is set on Nissan applications when the PCM (Powertrain Control Module) detects a break in communication over the CAN bus system for a period of longer than 2 seconds. Note that code U1000 on Nissan applications is a Class 2 communication malfunction, and therefore may or may not be accompanied by other generic or Nissan specific codes that identify at least the area in the CAN system where the fault occurred.

* Note that some resources list code U1000 as “SCP (J1850) Invalid or Missing Data for Primary Id”, while others do not list code U1000 as applying to Nissan at all. Therefore, this guide will discuss code U1000 as it applies to Nissan with the definition ““CAN Communication Line – Signal Malfunction”.

All modern vehicles are equipped with a CAN (Controller Area Network) serial communication system that interconnects all the control modules on the vehicle. Generally, CAN bus systems allow for extremely fast communication between all control modules, as well as communication between all control modules and the PCM, which acts as the “clearing house” for all communications between control modules. Put in simple terms, the purpose of the CAN bus system is to allow all control modules on the application to exchange information and data that controls, regulates, monitors, and verifies all aspects of that application’s operation.

All CAN bus systems consist of two interdependent circuits, one being the Can High circuit, and the other being the Can Low circuit, which allows not only for increased communication efficiencies, but also for increased fault detection capability. However, and as a practical matter, while all control modules on a CAN bus system can transmit and receive data some types of data carry a higher priority than other types of data. This is so because some faults are more serious than other faults, which means that data is exchanged between control modules on a strictly maintained priority basis, with higher priority data always enjoying priority over data with a lower priority.

In the case of code U1000, the fault involves a less-serious failure or malfunction, in the sense that the fault is unlikely to increase emissions, or cause damage to other systems and/or circuits if it is not resolved immediately. However, the trouble with this code is that it is not always accompanied by other codes that identify the area or system in which the communication failure had occurred, which can make it very difficult to isolate the communication failure.

In practice though, if there are no additional codes present, there are often also no symptoms present, apart from a stored trouble code. However, if other codes are present, the symptoms are often related to the codes, although some symptoms that might be present are often nebulous, in the sense that there is often no clearly discernible connection between the symptoms and the additional codes. Typical examples of this might be a hard, or no start condition, frequent, and unpredictable engine stalling, fluctuating idling speed, and varying degrees of power loss, when no codes that are directly indicative of these issues are present.

Where is the U1000 sensor located?

The image above shows a simplified representation of how a CAN bus system interconnects a multitude of control modules and systems on a typical Nissan application. In practice, a typical CAN bus serial communication system consists of several miles of wiring, thousands of circuits, and even more thousands of connections that link several dozen control modules together. For this reason, it is almost always easier and more cost effective to seek professional assistance when dealing with CAN bus related codes.

What are the common causes of code U1000?

In cases where code U1000 is present without additional codes, the code may merely be the result of a momentary glitch in this incredibly complex system, or sometimes for no apparent reason-especially when there no symptoms of any kind are present.

Nevertheless, some common causes of code U1000 could include the following-

  • Loss of ground integrity almost anywhere in the CAN bus system
  • Unlike most other faults, the failure of the PCM or one or more other control modules is a distinct possibility
  • Damaged, burnt, shorted, disconnected, or corroded wiring and/or connectors almost anywhere in the CAN bus system

WARNING: Due to the complexity of the CAN bus system, attempting to diagnosing and/or repair code U1000 is NOT a recommended procedure for non-professional mechanics. Lack of expert level knowledge of CAN bus systems, or ill-considered diagnostic methods could cause fatal damage to the affected vehicles’ electrical system, so play it safe, and refer the affected vehicle to the dealer or other competent repair facility for professional diagnosis and repair.

BAT Team Discussions for U1000

  • 03 grand am no start
    The MAP is reading in inches of mercury. I went and had a 100. 00 scan done. Codes in the memory were : U1000-U1016-B1374-U1088 and U1128. Think I should put a MAP sensor in?...
  • 2011 Nissan Maxima CAN lines
    I do NOT see NTB 10066 listed for a 2011 missan maxima S 3.5L. USA the U1000 is attached (useless) - will add if I find something thinking a starter circuit MAY be helpful...
  • QX56 Tach & speedometer problem
    A U1000 code is a CAN line communication network problem. If it indicates a U1001, it will not illuminate the check engine light....
  • link test
    P0010 P1020 P2030 P3040 hiyap0010go U1000 C1000 B1000 X0100...
  • 2004 chevy cavalier
    [I]Please fill out the following to ask a question.[/I] [B]MAKE[/B]: chevrolet [B]MODEL[/B]: cavalier [B]YEAR[/B]: 2004 [B]MILES[/B]: 209000 [B]ENGINE[/B]: 2,2 ecotech [B]DESCRIBE ISSUE[/B]....suddenly lost reverse, 1st 3rd and 4th gears (auto trans) dtc set with codes p0756 p0730 p0530 u1000 u106...