U1000 – Is Your Car’s Communications Network Down?

Within most modern vehicles, there’s a vast array of computers, sensors, wires, and a bunch of other miscellaneous electronics working in unison. Sensors transmit data through wiring harnesses, which a central command module or computer can analyze, react to, and actuate. In doing so, cars today are much more efficient and performant than ever before… Until a U1000 error code appears.

While all these gadgets do increase the risk of failure (thus, the need for constant repairs), we can at least count on your car’s onboard diagnostics. It’s just that simple to identify faults, including issues that pertain to the wiring itself. This is where a U1000 diagnostics trouble code might pop up if your car’s been acting up lately. So, what does ‘U1000’ mean, and what can you do to solve it?

It throws you off-guard just a tiny bit since you’re likely used to error codes starting with the letter, P. Indeed, U1000 is a manufacturer-specific code that’ll only relate to vehicles made by a select group of automakers. Nonetheless, they all point towards issues with your vehicle’s Communications Area Network (CAN) bus system. Defects in the latter can cause serious conflicts with your car.

How Do Your Car’s Electronics Work, Anyway?

Before we can learn more about U1000, we should take some time to understand more about what a ‘Communications Area Network‘ is. With that in mind, let’s remind ourselves of the intricate nature of modern car electronics. Most key components, from individual parts of the engine to the working of the brakes and even tire pressure status, are all monitored by a myriad of sensors.

These sensors relay data back to central modules or computers for analysis. For example, the engine has an ‘Engine Control Unit‘, which can sometimes be referred to as the ‘Powertrain Control Module‘ or the ‘Engine Control Module’. That’s ECU, PCM, and ECM, respectively. This one computer alone is responsible for keeping the engine in check, by monitoring temperature, airflow, timing, and more.

Altogether, the ECU ensures that your engine will always be in peak condition. If certain parts fail to perform well enough, the ECU will try to compensate and diagnose. Or, it’ll throw a warning light to let you know that something’s amiss. It practically runs the engine. For instance, the ECU will decide how much fuel to pump into the engine for combustion, depending on how much oxygen there is.

This occurs nearly instantaneously, as soon as you press the throttle pedal. Your car also has other, similar computers. For example, the ‘Transmission Control Module‘ or TCM. It works alongside the ECU to determine the right time to shift gears. Or, there’s the ‘Body Control Module‘ or BCM. This is the computer responsible for monitoring your air conditioning, headlights, wipers, and so on.

What Is A Communications Area Network (CAN), Then?

With all that being said, how do all those sensors communicate seamlessly with the modules? Not to mention, being able to do so swiftly and reliably, ensuring that your car can drive perfectly? It’s thanks to the CAN bus system that this is possible. Also known as ‘Communications Area Network’, it functions as a message-based protocol, passing along electronic signals and input within your car.

For instance, how can a tire pressure sensor’s input on PSI readings be transmitted and read through your car’s ECU to warn you that the tires are running a bit flat? This is done via the CAN bus system, by creating a standardized communications interface for all of your car’s electronics. Data is passed around throughout your car using a complex series of wiring harnesses and connectors.

This then ends up communication with CAN microcontroller chips, which transmit data to relevant vehicle subsystems. Remember, your vehicle can have as many as 70 or more electronic subsystems, each performing similar roles to the ECU. All subsystems within a single car must be able to maintain interconnectivity. This is to the benefit of fuel economy, emissions control (to learn more, check out our explainer on what is the catalytic converter), and safety.

Among others, like improving performance, enhancing driveability, or additional features such as managing autonomous driving. Therefore, we could now begin to see the benefits that a CAN bus system provides to a vehicle. In short, enabling differing electronics subsystems, computers, as well as sensors, all of which are made and programmed by different companies, to speak with one another.

What Benefits Do CAN Bus Systems Provide?

Besides being a platform for effortless and speedy data transmission between your car’s electronics, a CAN bus system features an abundance of benefits over traditional protocols, too:

  • Low Cost And Simple – In the old days, data flow between components had to be hard-wired through complicated analog signals. In stark contrast, a streamlined CAN bus system is simpler, cheaper, lighter (it doesn’t require as much heavy cabling), and works more reliably (data error reduction).
  • Centralized Control – With a CAN bus system, data transmission is centralized within its microchips. This ensures that data can be processed and sent out accordingly at speeds much faster than older protocols. Plus, it makes the diagnosis, data collection, as well as input configuration much easier.
  • Durable – Compared to the old methods of heavy, insulated wiring, a modernized CAN bus system is far more robust. It’s less susceptible to wear and tear from heat or vibrations. In addition, it won’t be as easily impacted by electromagnetic interference or other electrical gremlins.

  • Modularity – Older analog messaging protocols are hard to program and are rudimentary at best, which limits their functionality. Meanwhile, a CAN bus system is heavily customizable, and is as ubiquitous and widely supported within the car industry, just as USB is for computers.
  • Fast – Despite having, at times, over a mile’s worth of wiring, old analog systems are terribly slow. All the while, CAN could transmit data as quickly as 1Mbps. Additionally, it’s able to optimize the speed of data transmission by automatically prioritizing certain traffic over others.
  • Fault Detection – All CAN bus systems have built-in error detection. This ensures that problems with data transmission can be found on the fly. Moreover, CAN bus systems are also able to correct these faults in real-time, by reconfiguring or retransmitting the correct information.

What Does A U1000 Error Code Mean, Exactly?

While CAN bus systems mark a massive leap forward in technology compared to relatively ancient tech, it’s not invulnerable. Sometimes, the entire CAN module itself might be faulty, or it might be down to bad or compromised wiring. In either situation, a U1000 error code will appear if you plug an OBD diagnostics tool into your car. As we mentioned, this error is manufacturer-specific.

This means that it doesn’t conform to a standardized definition, as is determined by the Society of Automotive Engineers or SAE. Usually, you’ll find this error code appear on cars made by General Motors (which includes its subsidiary brands like GMC or Chevrolet), Nissan, Infiniti (a luxury sister brand to Nissan), as well as Isuzu. Depending on your car, the definition may vary slightly:

  • General Motors – “Class 2 Communications Malfunction Conditions”
  • Nissan – “CAN Communication Circuit”
  • Infiniti – “CAN Communication Line – Signal Malfunction”
  • Isuzu – “Class 2 Communication ID Not Learned”

CAN Bus Network

As we can see, at least, they all point to the same point of failure, your CAN bus system. This trouble code comes up if your OBD scanner finds there is a 2 or more second break in data transmission within the CAN controller. This is its cue that information flow between your car’s electronics might have been compromised. In other words, modules or sensors aren’t communicating properly.

Without a sufficient high-speed information flow over the CAN network, it might begin to affect how certain parts of your car may perform. The inability for modules to transmit input to each other can handicap your vehicle’s driveability, performance, efficiency, among others. Worse, a faulty CAN or wiring might also prevent serious problems from being reported, such as issues with the engine.

What Causes A U100 Error Code To Appear?

There could be numerous reasons why your car’s CAN bus system isn’t working well, hence popping up a U1000 error code. We have to consider the fact that U1000 is specific to each automaker, and it’s subsequently difficult to nail down what the root cause might have been. Among the most common causes of why you’re seeing a U1000 error code, in general, include:

  • Bad wiring or connection within and around the CAN bus system.
  • Loose or damaged connectors to and from the CAN module.
  • Corrosion or visible signs of damage on wires’ connector pins.
  • Short-circuiting or a bad ground connection.
  • Certain subsystems are running on old, incompatible software.
  • Faulty ECU (aka ECM or PCM) module, or a similar module.
  • Faulty CAN microcontroller chips or around the bus.


When conducting a diagnosis, it’s helpful to look at secondary OBD error codes. This helps to pinpoint the precise cause of the U1000 code, and what component or subsystem is at fault. Nissan-branded cars, for instance, can trigger a U1000 code because of a broken wiper. It’s important to understand that one brand’s U1000 may not be triggered for the same reasons as that of a different brand.

In certain marques, the way a U1000 code is detected also differs. With the ignition turned off, your car’s ECU and other modules go into sleep mode. This is to prevent overloading the battery. Their sleep mode should be activated within seconds (depending on the brand). For example, if the pre-set sleep mode timing is 5 seconds, and your modules sleep 6 seconds later, a U1000 code will appear.

What Are The Symptoms For A U1000 Error Code?

Besides seeing that U1000 error message on your OBD scanner tool, are there any other ways that’ll enable you to identify it? Well, if you’re only seeing a U1000 error code on its lonesome without any secondary codes, it might be hard to notice alternative symptoms. In some cases, it might appear as a result of a momentary glitch in the software, which should clear itself out in time.

Otherwise, you might be able to sneakily sense adverse changes in your car’s driveability owing to a fault in the CAN bus network. We’ve also discussed the communications network in our guide on the U0073 code. If we look at Nissan (where U1000 error codes commonly come up), a few of the symptoms that you might notice include:

Remember, U1000 is specific to manufacturers. The abovementioned symptoms apply commonly to Nissan-branded cars. Elsewhere, the symptoms will vary with GM or Isuzu-made vehicles, as U1000 is tied to other issues that are more particular within your car’s electronics. These symptoms might otherwise include (but aren’t limited to):

As a whole, a CAN network failure or fault isn’t the most serious issue to impact your car. However, this notion does differ based on what vehicle you drive. With a Nissan, U1000 could gravely affect a car’s driveability and performance. As for the other brands where U1000 applies, it’s not always as urgent to fix, and it may merely represent an inconvenience rather than permanently damaging.

How Can You Diagnose Or Test A U1000 Error Code?

Unfortunately, we don’t recommend a DIY solution for diagnosis, and it’s best to leave this down to the professionals. This is simply due to the complex nature of a CAN network. We’re talking about a mile’s worth of wiring or more. Between that, there are thousands of circuits and connectors, which link nearly 70 modules together. As such, improper diagnosis could lead to more harm than good.


If you’re sending your car off for a check-up at the local workshop, there are several techniques that they employ to more easily diagnose U1000:

  1. Identify accompanying trouble codes (if any, besides U1000), that might more specifically point to a component at fault.
  2. Analyze and refer to Technical Service Bulletins (TSBs) issued by the automaker, which could outline the right diagnostics to proceed with.
  3. Inspect and consult wiring diagrams specific to the make and model of your vehicle, with a particular focus on the connection points.
  4. Check and clean out all ground connections, pins, and connectors that link up the wiring to the rest of the CAN network.
  5. Look at the wiring harnesses and cables for visible signs of damage, such as fraying, short-circuits, burn marks, loose connectors, or corrosion.
  6. Clear the U1000 error code stored in your car, and see if the code returns, as it can sometimes come up as a temporary glitch.
  7. Hook up a multimeter to the CAN network to ensure that the ground connection is good, as well as make sure there’s sufficient resistance, without a drop in voltage readings.
  8. Trial and error by disconnecting the CAN bus network from individual modules, connectors, wires, or sensors to help isolate the issue.
  9. Refer to a make or model-specific service manual to determine if it’s a fault with the CAN network, or if it’s a module-related problem.

How Can You Solve A U1000 Error Code?

Given the wide variety of underlying issues that could trigger a U1000 error code, what you may do to solve it varies significantly. If it’s merely due to a momentary glitch, you need only clear out the error codes, and restart the engine. After that, the U1000 code should no longer appear. If it does, then you’ll have to worry about fixing or replacing the compromised components.

On occasions, you’re able to solve a U1000 error code by re-flashing or resetting the ECU. A detailed reprogramming of the car’s central computer module is fairly simple and costs you between $100 to $200 on average. Another typical reason why you’re seeing a U1000 error code might be pinned on faulty wiring. The solution is highly dependent on the section of wires that it’s affected by.

If it’s merely one or a few wires or connectors, it shouldn’t cost much. However, if the entire wiring harness needs to be replaced, it can cost you upwards of $1,000 to do. In some cases, nearly $2,000, seeing how complicated the wiring on your car is. Then, we’ll have to think about the possibility that one or more modules are damaged. In such a scenario, these modules will have to be replaced.

A new ECU isn’t cheap and could set you back between $500 to as high as $3,000 with some cars. If the modules controlling your air conditioning or automated headlights are broken, they’re typically in the range of $100 to $400 each. Only after a thorough diagnosis is complete, and your mechanic has identified what is at fault, can you realize the necessary steps and costs towards solving it.

Should You Have A U1000 Error Code Addressed Right Away?

As we’ve highlighted already, a U1000 error code may or may not be consequential. In some cars, a U1000 trouble code is tied to significant issues with your car’s driveability. Refusing to have it fixed in an instant may lead to poor performance, hesitant acceleration, or problems with even starting the engine. If this is the case for you, then a bad CAN network should definitely be fixed ASAP.

Alas, if you happen to drive a vehicle whereby U1000 is marked as a less-than-serious alert by those who manufactured it, then you needn’t worry right away. It’s not likely to cause that much trouble out of the gate. For example, causing long-term damage to your car, increasing fuel economy, raising emissions, and so forth. If this is so, then you may think about putting off fixing for a little while.


Nevertheless, we don’t recommend this, given the complex nature of the CAN network, and how this interacts with the rest of your car’s electronics. Our top tip, upon seeing a U1000 trouble code show up with a quick OBD scan, is to look at what other error codes appear alongside it. This can provide you with context as to the seriousness of what you’re dealing with, whether it’s merely the CAN.

It’s still best to head over to a local mechanic as soon as U1000 appears. Even if it turns out to be a fairly small issue, after all, letting your electronics run amok is a terrible mistake. Doing so may alter how your car behaves. Furthermore, and without the modules (ECU, TCM, BCM, etc.) working in an optimized manner, there’s a heightened risk of you accelerating wear onto your car.

Facts about Fixing the U1000 Code in Vehicles:

  1. The U1000 code is a manufacturer-specific OBD-2 Trouble Code that indicates problems with a vehicle’s communication system.
  2. The code is triggered by a failure in the car’s Controller Area Network (CAN) Data Bus System, which affects the car’s performance over time.
  3. Symptoms of a U1000 code error may include the Check Engine light, engine stalling, hesitation, or failure to start, and inoperable HVAC system, among others.
  4. The severity of the U1000 code varies depending on the manufacturer, with Nissan cars describing it as a potential threat to drivability.
  5. The CAN-bus system is a communication interface that relays data through complex electrical connections from one point to another in the car.
  6. The CAN-bus system consists of multiple modules with specific functions, such as the ECM, TCM, and BCM, that collect and relay data to monitor engine performance and control shift timing, among others.
  7. The U1000 code can be triggered by faulty control modules or circuits, damaged/corroded wiring, or a bad connector contact at the module junction/wiring harness.
  8. Fixing the U1000 code requires proper diagnosis to identify and fix the specific cause, and replacing a module requires manufacturer-specific software for “flashing.”
  9. Diagnosis involves scanning the code, recording all other active DTC, and inspecting the connections and clear all ground connections to the CAN-bus system.
  10. The cost of fixing the U1000 code varies depending on the shop and the vehicle model, with an ECM replacement costing around $800 to $2000, including labor costs and other fees.

Final Thoughts On CAN Network Problems And U1000

That then is a great place to round up our look at a U1000 diagnostics trouble code. The first production vehicle to featured it came about in 1991 with the Mercedes W140. But since then, the CAN bus system has evolved rapidly over the years. Practically every production vehicle since 2008 has had one. It’s not only present on passenger cars, commercial trucks, and other road-going vehicles, either.

CAN messaging protocols are being deployed in industrial machinery and aviation equipment. As well as in escalators or elevators, medical instruments, shipping and maritime gear. And, so much more besides that. This highlights just how reliant we are on electronic devices. Not to mention, their ability to speak to and interconnect various modules, sensors, actuators, and other gadgets together seamlessly.

They may present a win-win-win case against old-school analog, but faults do exist. Primarily, it could be the case that the CAN microcontroller chips or module might have been corrupted. Or, the wiring that connects to it isn’t in the best shape. That’s beside the possibility of individual parts that you’ll find communicating with the CAN network breaking or going offline entirely.

The lack of standardization for a U1000 error code can make it challenging to diagnose the cause of why it appears. Ultimately, impacts how easy or difficult it’ll be when it comes time to fix it, and how much it’ll cost you. Your car’s entire wiring harness might need an overhaul, or it might require a simple software reset. It’s never a good idea to put it off for long, though.

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