U0073 Code: Control Module Communication Bus “A” Off

What Does the U0073 Code Mean?

Diagnostic trouble code (DTC) U0073 stands for “Control Module Communication Bus “A” Off.” OBD code U0073  is a communication system DTC that applies to most vehicles. Usually, this code is triggered when communication is lost intermittently or fully between your vehicle’s control modules.

U0073 is a communication system diagnostic code related to your CANbus. This code can register in a variety of modules, including the PCM, TCM, anti-lock braking system (ABS), or body control module (BCM).

An In-Depth Look at Code U0073 

Your vehicle’s data network is much like a human body’s nervous system, as it connects various modules. For example, a 2019 F150 (depending on its equipment package) may have 40 modules, all of which communicate with each other. Many vehicles have far more modules than 40, and there are switches embedded in modules that send the switch signals over the network on some of them. 

Pro Tips are nuggets of information direct from ASE-certified automobile technicians working with CarParts.com, which may include unique, personal insights based on their years of experience working in the automotive industry. These can help you make more informed decisions about your car.

Pro Tip: There are high and low-speed networks, one-wire and two-wire networks, and modules on the vehicle network that act as translators. They receive input from the various networks and send them out to the modules that need the information.

The U0073 code doesn’t apply to all newer vehicles. It mostly applies to vehicles equipped with the faster network referred to as the CAN bus, of which there are different speeds. CAN bus speeds are determined by the importance of the information the CAN bus is expected to deliver. 

The U0073 code doesn’t apply to all newer vehicles. It mostly applies to vehicles equipped with the faster network referred to as the CAN bus, of which there are different speeds. CAN bus speeds are determined by the importance of the information the CAN bus is expected to deliver.

–Richard McCuistian, ASE Certified Master Automobile Technician

The fastest CAN busses do the most time-sensitive work on vehicles, particularly powertrain (engine/transmission) control, vehicle dynamics, etc. More recently, engine control modules (ECM) and transmission control modules (TCM) are separate modules rather than being concentrated in just one powertrain control module (PCM). Thus, some of the more important information exchanged between modules are the messages between the ECM and TCM during normal driving.

With that in mind, just about any issue a vehicle may have can be network-related, thus the bevy of Uxxx codes that can be set in modern vehicle systems.

Unexpected issues can cause network codes. For instance, a 2007 Cadillac Escalade can have a flashing traction control light and a stored network code due to extremely high fuel pressure from an in-tank pump with a bad fuel pressure regulator. With that in mind, note that Uxxx codes aren’t typically DIY serviceable beyond checking fuses, examining module connections, or looking for chafed or damaged wire harnesses. Moisture intrusion on vehicles with body water leaks can be an issue as well, and just about any module that has to be replaced must have some programming done.

What are the Possible Causes of the U0073 Code? 

Here are some of the possible causes that could trigger the U0073 code: 

• An issue with one of the control modules
• A data network problem
• A circuit problem, such as damaged wiring or a poor connection 

What are the Common Symptoms of the U0073 Code? 

Common symptoms associated with the code include the following: 

• Illuminated check engine light
• Loss of engine power
• Reduced fuel economy
• A possible no-crank or no-starting condition
• A driver information message (DIC) message is displayed
• Transmission won’t shift
• Various other symptoms too numerous to list 

How to Diagnose the U0073 Code

Resolving code U0073 can be challenging. It is usually best to leave the job to trusted professionals with the tools to isolate the concern and repair it. 

However, if you’re confident about your DIY repair skills, here is a video you can watch to help you learn more about code U0073 diagnosis:

How to Fix the U0073 Code 

Fixing the U0073 code can be tricky, especially since solutions can vary depending on your vehicle’s make and model. With that being said, a few things you can attempt include:

Battery Check

Do a quick check on your vehicle’s battery to see if it’s still running strong. Low power can lead to the U0073 code being flashed.

Other DTC Logs

Using a code reader, you can check for other DTC logs that might be linked to the U0073 code. Addressing the other logs might also solve U0073.

Visual Inspection

Do a quick visual inspection of the CANbus area. Any broken wires or loose connectors can trigger the U0073 code. Replacing or repairing these parts might be the simple solution you need to fixing U0073.

Technical Service Bulletins (TSBs)

Keep an eye out for any TSBs from your vehicle’s manufacturer about your vehicle’s model and year. These bulletins will often let you know if there’s a specific problem linked to your vehicle’s model that needs addressing and how to get it fixed.

Seek Professional Assistance

The CANbus module is an especially complex system that you need to be familiar with before making any type of repair. We recommend contacting a licensed mechanic for their assistance rather than attempting further repairs by yourself. Here are the steps a professional might need to do:

• Check the battery level and all the connections to the CANbus unit to ensure everything is clean and tight.
• Using a scanner, a professional can read any diagnostic trouble codes that the system memory has stored. This allows them to compare the codes to the manufacturer’s diagnostics codes and identify the problem faster.
• Using a different scanning tool to confirm the continuity in all CANbus ‘A’ modules.
• Test-drive the vehicle and test that each module is communicating with the diagnostic computer.
• Troubleshoot the different components to test if any parts are prone to failure.
• Once they identify the issues, they can replace the problematic components, including the ECM, with parts using identical configurations and vehicle identification numbers (VIN).
• Test-drive the vehicle a final time after replacing the components.

Products Mentioned in this Guide

Body Control Module Engine Control Module Transmission Control Module