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U1000 Code – What Does It Mean & How To Fix It

This is one of the most frequent OBD2 trouble codes. Read the full article below to know what it means, how to fix it, and what other codes may show related to it.

Definition

A U1000 trouble code is a code mainly occurring in Chevrolets, GMCs and Nissans, though this article will focus primarily on the code as it relates to Nissans. A U1000 is commonly referred to as CAN Communication Line - Signal Malfunction, and is registered by a car’s OBD when it detects a 2 second or more break in communication in the CAN bus system.

A CAN bus communications network allows fast communication between a car's various modules, and has appeared in almost every car made since 2008. Each module in a car has its own identification code which it uses to send messages to the Engine Control Unit (ECU) through the CAN communication line. However, when this communication line fails, it causes a U1000.

A U1000 is a Class 2 communications malfunction, which means that there may not be any other symptoms present. However, if there is another symptom, that may actually help, as it could pinpoint where in your CAN bus system the communication failed. If a U1000 code stands alone, however, that means there are no other observable problems, and the CAN bus itself is simply faulty.  

Causes

Because the CAN bus system has modules all over the car, the problem can be located almost anywhere. Finding what is wrong may take time.

One of the most common reasons why a U1000 shows up is because of faulty wiring somewhere in the cars CAN bus system. It will take extensive searching to locate the damaged, shorted, disconnected or eroded wire, so be patient.

Of course, it could also be nothing at all--just a minor glitches. For example, a U1000 code could register if the ECM and modules don’t shut down soon enough after the car is turned off. After the key is removed from the ignition, the ECM and module go to sleep after five seconds to save battery power, however, if they do not turn off within that period of time, a U1000 code will be noted by the OBD. 

Symptoms

As a Class 2 communication malfunction, a U1000 does not have to come with any external manifestations. However, if the U1000 is responding to the failed message of some other code, the symptoms could include anything from improperly functioning headlights/air conditioner to poor engine performance to engine stalling. In Nissans particularly, symptoms of a U1000 have been known to present as engine stalling, low power, and an inability to turn on.  

Diagnosis

To diagnose a U1000, several steps should be taken. First, clear the U1000 code and check to see if it returns. If it doesn’t return for some time, then it was probably just a glitch in the system.

If it does return, though, you’re going to need to perform a visual inspection to look for broken/loose wires and connections. If no problem can be detected, a technician will need to check the control module to see if it’s working properly.

Finally, if none of the modules are having any problems, it is probably the network itself. This will need to be checked with a digital multimeter (DMM). After a DMM is hooked to the diagnostic port, it will send signals throughout the car to search for network shorts.

Common mistakes

While many people may be tempted to diagnose a U1000 on their own, it is not advised. The Can bus system is extremely complex, and tampering with it without proper knowledge of car repair procedures could cause permanent damage to a car's internal wiring and computational systems. Have a trained professional handle this for you.

How serious is this?

On its own, a U1000 trouble code is not serious, however, a break in communication between your car's OBD modules could prevent it from alerting you of something more problematic, like an ignition failure or a cylinder misfire. Therefore, a U1000 should not be ignored for very long as it is often accompanied by other symptoms.

What repairs can fix the code?

As there are many things that can trigger a U1000, there are also many different ways the problem may need to be remedied.

As stated above, if it is just a temporary glitch, if you clear the code and restart the engine, the problem may disappear on its own.

If that doesn’t work, the next step is to do a roll call of the various modules using a diagnostic scan tool. This scan tool addressed each module in your car one at a time. If one of the modules does not respond, it will have to be repaired or replaced.

Finally, if it is not a specific module at fault, then the network itself may be the problem. If the DMM detects a short somewhere in the network, you’ll know it’s a wiring problem. These wires can be quickly replaced once you know where they are.

Related codes

Another code like the U1000 is the U1001 which indicates the ECM cannot send or receive communication signals. And a U1002 means that it is the BCM which is at fault.

Conclusion

The U1000 trouble code is not like many other codes, as it refers to a problem with the car's OBD itself, rather than its mechanical functions. Although a U1000 does not automatically mean your car is in danger, if the cars modules are not communicating properly, it increases the risk of other problems in the future. 

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