How to Fix U1000 Code: CAN Communication Line Signal-Malfunction

OBD2 Scanners is reader-supported. When you buy through links on our site, we may earn an affiliate commission.

If your car's warning light illuminates and you see the U1000 code, that is something to take seriously. It is trying to tell you that an issue needs to be addressed. However, don't panic because there are several fixes you can do to repair the problem.

This blog post will discuss the common causes of U1000 errors, symptoms, and how to fix them. So, if your car's engine has been giving you trouble, read on for help!

What is Code U1000?

Code U1000 is a diagnostic trouble code for Controller Area Network (CAN) Communication Line Signal-Malfunction. This error code triggers when the Powertrain Control Module (PCM) detects a 2 second or more break in communication in the CAN bus system. This means that a faulty module affects the communication signal between different modules in your car.

The code u1000 is commonly found in Nissan cars but can occur in other makes and models, such as Chevrolet and GMC. There are various control modules in your vehicle that communicate with each other, and one of those is the Transmission Control Module (TCM). When the TCM cannot communicate with the other modules, it will throw this code.

Symptoms of Code U1000

When the control modules are not communicating, it will cause different problems in your car. Some of the symptoms are:

  • The Check Engine light is on.
  • The vehicle will not start.
  • There is a loss of power.
  • The transmission shifts hard or does not shift at all.
  • Engine stalling

Causes of Code U1000

Now that you know what this code means and its symptoms, you may be thinking of fixing this issue, but hold off because you will need to know the cause to fix this. The most reasons for this code are:

  • Damaged wiring in the CAN bus system
  • Bad ground connection
  • Corroded wiring
  • Faulty Engine Control Module (ECM)
  • Poor engine performance

How to Diagnose Error Code U1000?

Now that we have narrowed all possible causes for this code, it is time to diagnose your car, so we can do possible fixes to remove it. If you have some knowledge of vehicles and how they work, you may be able to fix this problem yourself. Let’s start by doing this:

Note: The CAN bus system is quite complicated, and tampering with it without adequate knowledge of automobile repair procedures may result in long-term damage to a vehicle's internal wiring and computational systems.

Check the Manufacturers (TBS) Technical Service Bulletins 

First and foremost, you want to check the manufacturer's TSBs or technical service bulletins. These are instructions on how to fix common problems that have been reported. Often, the U1000 error code will be listed here with a solution.

Use a Diagnostic Code Reader

If there are no TSB s for your specific car, you can try using a diagnostic code reader. This device plugs into the computer in your car and reads the error codes. It will then tell you what the problem is.

Using the OBD scanner, check for additional codes that triggered along with the U1000 code. If there are other codes, they need to be fixed before addressing the U1000 code. More often than not, these codes are related, and fixing one will also fix the others.

Check Wiring

If you're still having trouble fixing the U1000 error code, the wiring may be the issue that is especially common in older vehicles. Check the wirings to ensure it's not damaged or frayed. If it is, you'll need to replace it.

Inspect the related wiring harness and connectors. Check for damaged components and look for broken, bent, pushed out, or corroded connector pins. If any damage is found, replace or repair it. 

While you're inspecting the wiring, also check for loose connections. Make sure all connectors are securely fastened and connected correctly. Also, check for ground connections and make sure they are clean and tight.

How to Fix Code U1000?

If, after diagnosing all the possible causes and taking the appropriate corrective actions, the U1000 code persists, then you may have a defective transmission control module. Changing the TCM is simple since it's right behind the battery on most cars. 

Finding it, on the other hand, might be difficult. In addition, because a new component will need to be calibrated, this job is typically best suited for an expert mechanic. However, if you feel comfortable undertaking the task, it's a job that you can do at home with the right tools and instructions. To perform it:

  1. Disconnect the negative battery cable.
  2. Then remove the cover panel over the TCM.
  3. Locate the TCM. It's a black box with several plugs coming out of it, and it's mounted on or near the                firewall.
  4. Unplug all the connectors from the TCM.
  5. Remove the two bolts holding the TCM in place, then carefully remove it from its mount.
  6. Now you can access the TCM's internal workings. Using a small screwdriver, gently pry the top off the              TCM. 
  7. Install the new TCM in the reverse order of removing the old one.
  8. Reconnect all the plugs and connectors, then bolt the TCM back into place.
  9. Reconnect the battery, start the ignition, and test your vehicle for proper operation.

Your engine should now be running correctly again if you've successfully repaired the TCM. But if the problem persists, you may need to replace the PCM. If you are unsure of doing this, you may check our guide on replacing a PCM.

Common Mistakes When Diagnosing the U1000 Code

Now that you know how to fix the code U1000, there are a few common mistakes that you should avoid when diagnosing and repairing this issue.

  • Not checking for any other related codes that may be stored in the vehicle's computer.
  • Not checking the wirings before replacing components.

Code U1000 FAQs

1. Is the U1000 code serious?

Since the root of this error code issue is the CAN bus (controller area network) within the network of wires and modules in your car, it is considered severe.

2. Is it safe to drive with this code? 

Although the U1000 code does not automatically mean your car is in danger, it is still not safe to drive. Because if the car's modules are not communicating correctly, it increases the risk of other problems in the future.

3. Can a bad battery cause the U1000 code?

Yes, a bad battery can be one of the causes of this error code. It is crucial to have a healthy battery to prevent any electrical issues in your vehicle.

4. How much does it cost to diagnose the U1000 code?

The average cost to diagnose and repair a U1000 code is between $80 and $100. But as always, prices will vary depending on the severity of the issue. If replacing the TCM is necessary, that cost will be between $500 to $900, including the labor.

5. Is it safe to repair the wires, or it's better to replace them?

In most cases, repairing the wires is a safe and affordable option. However, if the damage to the wiring is too extensive, it may be necessary to replace them.


If your car's Check Engine Light illuminates and you see the U1000 code, don't panic! There are several fixes you can do to repair the issue. However, you must take this seriously and address the problem as soon as possible.

We hope this guide has helped fix your problem with the code U1000. Have any other questions? Feel free to reach out to us for more help.