How to Fix U0073 Code: Control Module Communication Bus A Off

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When your Check Engine Light illuminates your car dashboard, it is something you should not ignore, especially when your OBD scanner is throwing the U0073 Code. So what is this code? 

Is it something you need to address as soon as possible? If you have this error code on your scanner, don't worry, as we will walk you through diagnosing and fixing this yourself! Let's get started!

What is Code U0073?

The U0073 is a diagnostic trouble code for "Control Module Communication Bus A Off." This code typically applies to domestic and import fuel injected engines manufactured since 2004, including Chevrolet, Cadillac, Ford, GMC, and Honda.

This trouble code indicates a communication problem with the Controller Area Network (CAN) bus and control modules. When the CAN bus is "off," the car's computer system cannot communicate with various modules, including the (PCM) Powertrain Control Module, transmission control module (TCM), and an anti-lock braking system (ABS) controller.

Symptoms of Code U0073

When your vehicle has this error code, the Check Engine Light will come on. Aside from that, you may all experience all these symptoms below:

  • Lack of engine power
  • Not starting
  • Poor fuel economy
  • The indicator of all instrument clusters is "on."
  • Vehicle stops while driving
  • Not working HVAC

Causes of Code U0073

Just like any transmission-related trouble code, this code is caused by the following reasons:

  • Loose ground wire connection of the transmission control module
  • Shorted circuit "A."
  • Damaged CAN bus
  • Open or shorted harness
  • Damaged TCM

How to Diagnose Error Code U0073?

Diagnosing this error code may vary depending on several things, such as your car manufacturer, number of wire colors, and type of communications system. Also, make sure that you have experience reading wiring diagrams and using a digital multimeter, as it will be part of the process. When you are ready, let's start!

Consult your Technical Service Bulletin (TSB)

Before you start, it is best to consult your TSB or Technical Service Bulletin. This document can provide you with the diagnostic procedures and causes of a particular trouble code. You can find the exact steps to repair the issue if you are lucky.

Check for Other Trouble Codes

Scanning for other codes is the second step in this process. If you only have the U0073 code, there may be another issue, so it is best to rule out other causes. So, use your OBD scanner to look for additional codes and jot them down before moving on to the next steps.

Look for Broken or Damaged Wiring

One possible cause of the U0073 code is broken or damaged wiring and harness. Electrical shorts can cause issues and should be repaired as soon as possible. Locate all CAN bus communication wires and inspect for damage. If you find any issues, repair them, then continue to the next steps. 

Clear the Codes

If you have made any repairs or replaced any parts, it is always good to clear the diagnostic trouble codes and scan them again. This will help you determine if the repairs successfully fixed the U0073 code. 

If the code does not return, you know that the repairs were successful, and you can move on. But if the code returns, proceed to advanced repairs.

How to Fix Code U0073

If you have made any repairs and replacements, but the U0073 code is still present, then it is likely that the problem is the CAN bus controller itself. In this case, you will need to replace the controller to fix the problem.

If you're not confident in fixing this issue, take your car to a professional mechanic, but If you are, let's proceed!

Step-by-Step Guide to Cleaning the CAN Bus

Like any transmission problem, a dirty CAN bus is one of the most common causes of the U0073 code. Luckily, this is one of the easiest problems to fix. Here is the step-by-step guide.

  1. Disconnect the negative battery terminal to prevent any electrical shorts.
  2. Locate the CAN bus wires coming from the controller. These will usually be two thin wires running side-by-side.
  3. Gently wipe down the CAN bus wires using a clean rag and some isopropyl alcohol. You can also spray compressed air into all of the connectors on the CAN bus. Be sure to get in between all of the pins.
  4. Be careful not to damage the wires or disconnect them from the controller.
  5. Reconnect the negative battery terminal and start up your car. The U0073 code should now be gone.

Step-by-Step Guide to Testing the TCM Voltage

Another way to fix the U0073 code is by testing the voltage of the TCM. You can do this with a multimeter.

  1. First, locate the TCM on your vehicle. It is usually located near the battery. Once you have found it, remove the cover and locate the voltage terminal.
  2. Next, set your multimeter to the DC voltage setting and touch the black lead to the ground terminal. Then, touch the red lead to the voltage terminal.
  3. You should see a reading of around 12 volts. If you do not see this reading, there is an issue with the TCM, and it will need to be replaced.
  4. Once you have verified that the TCM has the correct voltage, you can move on to the next step.

If the code persists, there may be a more severe problem like a faulty TCM. In that case, you need to replace it with a new one.

Step-by-Step Guide to Replacing the TCM

Replacing the Transmission Control Module (TCM) is a pretty straightforward process if you are mechanically inclined; however, it is essential to follow these steps carefully to avoid damaging the new TCM.

  1. First, disconnect the negative battery terminal to prevent any accidental short circuits.
  2. Next, remove the TCM from its mount and disconnect all electrical connectors.
  3. After that, remove the bolts that hold the TCM in place and take it out.
  4. To install the new TCM, reverse these steps.

Common Mistakes When Diagnosing the Code U0073

There are a lot of causes that can trigger the U0073 code making it difficult to pinpoint the exact problem. So, what are these common mistakes you must know to avoid?

  • Not checking the battery voltage.
  • Ignoring other codes that may have been stored along with the U0073 code.
  • Not checking for loose and damaged wires and harnesses
  • Bypassing important steps along the way
  • Not having the proper tools and equipment to diagnose and repair the problem correctly.
  • Replacing parts that aren't the exact issue.

Code U0073 FAQs

1. Is the code U0073 serious?

It is considered serious because it is about the communications circuit between the vehicle's control modules. It could lead to a more severe problem if left unaddressed.

2. Is it safe to drive while having this diagnostic trouble code?

Driving with this error code on your car is unsafe because you may experience drivability issues and even make your car stop in the middle of the road.

3. Is it safe to diagnose it myself?

The answer will depend on your mechanical skills. If you are not confident in your abilities, it is best to take it to a professional mechanic.

4. What if the code returns after the TCM replacement?

There is a possibility that the code will return after the TCM replacement, primarily when you didn't diagnose the causes thoroughly. Always remember to scan for other codes before replacing any parts.

5. How much does the repair of code U0073 cost?

The cost to diagnose the code U0073 will depend on your location and the mechanic you take it to. However, most mechanics charge an hourly rate for their services. This means that you will have to provide a detailed description of what is happening with your car for them to give you an accurate estimate.

Conclusion

It may seem daunting at first, but fixing the diagnostic code U0073 is doable. By following the steps outlined in this blog post, you should be able to diagnose and fix the problem in no time. Consult your vehicle's owner's manual for more specific information on servicing your car. 

Have you fixed the code U0073 yet? We want to hear about your experience!