How to Fix U0100 Code: Troubleshooting and Repairing

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

laptop screen showing u0100 code

If you are driving and see the Check Engine Light come on, it can be a scary experience. You may not know what is wrong with your car or how much it will cost to fix. The same thing can happen when your OBD scanner shows the error code U0100.

But, don't worry, as this blog post will discuss the symptoms, causes, and how to fix the U0100 code. Let's get started!

What is Code U0100?

The U0100 is a diagnostic trouble code defined as Lost Communication with Powertrain Control Module (PCM). This means there is lost network communication between your Electronic Control Module (ECM) and one or more modules. There is a strong possibility of a problem with the CAN bus wiring disrupting the communications.

The Controller Area Network (CAN) bus is responsible for communication between all of the modules in your car. So, when there is a problem with it, it can affect how different systems in your car work, and the code U0100 will be set.

Symptoms of Code U0100

Some people may have been experiencing signs and symptoms related to the U0100 code, but they were not taking it seriously until their warning lights illuminated. If you're experiencing any of the symptoms below, don't think twice to diagnose the issue:

  • Check Engine Light is on
  • Vehicle stalling
  • Engine not starting

Causes of Code U0100

The U0100 code can be caused by communication errors, hardware failures, and software issues. Here are some of the causes you should be aware of:

  • Faulty connector or wiring issue
  • Incompatible performance computer chips installation
  • Defective pin terminal in one of the connectors (bent or pushed out)
  • Loose ground to the computer
  • Faulty PCM

How to Diagnose Error Code U0100?

Whether for hardware or software, every repairing process starts with a diagnosis. The same goes with this issue; it is essential to know what caused the error Code U0100 to fix it. To perform the diagnosis:

  1. Before you start diagnosing the U0100 code, it is crucial to scan for any other fault codes that may be present. This will help you identify the issue more efficiently. You can use a typical OBD scanner, but an advanced scanner is better.
  2. Inspect the wiring harness and connectors that lead to and from the PCM powertrain control module. Look for damaged, burnt, or loose wires and terminals. If damage is found, repair or replace it.
  3. If you find corroded connectors, use a wire brush to clean them and apply dielectric grease. Make sure the connector is completely dry before reconnecting it.
  4. Ensure the battery is charged so the PCM has a power supply to function.
  5. Check the C bus connector for damage. Then check for shorts on the (+) and (-) CAN C circuit using a multimeter. If everything looks correct, it's time to inspect the PCM.
  6. Check the (+) and (-) connections on your PCM with your multimeter. If there's no voltage, the PCM is likely bad and will need to be replaced.
  7. If you've replaced any parts or repaired any wiring, clear the codes and test drive the vehicle to make sure the problem has been fixed.

How to Fix Code U0100?

Now that you are done diagnosing all the causes of this error code, you probably know where the issue is coming from. If you find a problem with the CAN bus wiring, you can fix it yourself.

Step-by-Step Guide to Fixing the CAN bus Wiring

  1. Locate the CAN bus on your vehicle. The CAN bus location may vary depending on your vehicle manufacturer. (Check your manual)
  2. Once located, check all the particular module connection points on the CAN bus and ensure no loose or damaged wires.
  3. If you find damaged wires, cut them off and strip the ends. Then, twist the wire together and solder them.
  4. After soldering the wires, tape them up with electrical tape to insulate them.

If replacing or repairing the CAN bus did not solve the issue, don't worry, as you still have the last card! As mentioned above, the PCM is what communicates with the CAN bus. If you have a U0100 code, there is a communication error between these two parts.

The good news is you can replace the PCM yourself. However, if you are unsure where and how to start, you can visit our guide on replacing the PCM.

Common Mistakes When Diagnosing the Code U0100

As we have always said, diagnosing is very important when fixing an issue. So there is no room for misdiagnosis. However, if this is your first time fixing the U0100 code, there are some mistakes that you might make.

But don't worry, as we will list some of the common mistakes people make when diagnosing this error code so you can avoid them.

  • Thinking that the problem lies with the PCM without inspection of the CAN bus wirings.
  • Another is when they replace parts without running any tests first.
  • Some people forget to check for other codes related to the U0100 code.
  • Not diagnosing all the possible causes.
  • People often try to replace the ECU or TCU unit when replacing the PCM instead.
  • Not thoroughly diagnosing other module communication-related system codes. 

Code U0100 FAQs

1. Is the U0100 code serious?

Yes, because the vehicles with the U0100 error code may experience sudden halts while in operation. They might also refuse to restart, so it is considered severe and should be addressed immediately.

2. Can I drive with this error code?

It is recommended not to drive while having this issue because it will be hard to drive the car without communication between modules.

3. What should I do to prevent this code from coming back?

The best way to prevent this is to have regular check-ups and proper repairs.

4. How much does it cost to repair the code U0100?

The repair cost will depend on the severity of the symptoms and the exact reason to repair. If you're replacing the PCM, the ideal cost will be $500 to $1000.

5. Will this issue affect my emission test?

Yes, the issue will most likely affect your emission test because this can manifest drivability issues and trigger Check Engine Light.


The U0100 code is a serious issue that you should address as soon as possible as it may lead to more severe drivability issues.

So, if you have any symptoms related to this error code, don't think twice to fix it with the help of our guide. But if not mechanically inclined, take it to a reputable mechanic for further diagnosis and repairs.

Have you ever dealt with the U0100 code? What other tips do you have for troubleshooting and repairing this issue? Share your thoughts, comments, and suggestions below! Thanks for reading!