U0073 code solution: Control module communication bus A off

Last Updated on March 27, 2025

One of the most common yet confusing issues vehicle owners face is the U0073 trouble code. Many drivers are unaware of its cause or potential consequences. In this guide, we’ll explain everything you need to know about the U0073 code, including its meaning, causes, and symptoms.

What Does the U0073 Code Mean?

The U0073 code is a Diagnostic Trouble Code (DTC) that indicates a loss of communication in the Control Module Communication Bus “A”. This code is commonly triggered when your vehicle experiences a communication failure between critical modules such as the Powertrain Control Module (PCM), Transmission Control Module (TCM), Anti-lock Braking System (ABS), and Body Control Module (BCM).

The communication failure occurs within the Controller Area Network (CAN) bus, which acts as the central nervous system of your vehicle, allowing multiple control modules to share and transmit information.

The CAN Bus and Network Speed Modes

Most modern vehicles are equipped with more than 40 interconnected modules that communicate via the CAN bus system. These modules function like neurons in a human nervous system, constantly exchanging data for seamless vehicle operation.

There are two types of communication lines within the CAN bus:

• CAN High (fast speed)
• CAN Low (slow speed)

Additionally, the network may use single-wire or dual-wire configurations, depending on the system design. These modules act as translators—receiving input from one part of the vehicle and transmitting data to others.

Is the U0073 Code Common in Modern Vehicles?

Interestingly, the U0073 code is more frequently found in older vehicles, especially those where separate control modules (ECM and PCM) require higher-speed communication. In newer vehicles, these functions are often combined into a single Powertrain Control Module (PCM), which can reduce the likelihood of this specific code but increase the complexity of other Uxxxx network communication errors.

Possible Causes of the U0073 Trouble Code

Several factors can lead to a U0073 error code, including:

• Faulty or malfunctioning control modules
• Loose, broken, or corroded wiring connections
• Poor electrical grounds or open/short circuits
• Issues with the data network (CAN bus faults)

If you’re experiencing control module issues, also check out our guide on the C0800 Code: Control Module Power Circuit.

Symptoms of a U0073 Code

Here are the most common symptoms that may accompany the U0073 code:

• Loss of engine power or sudden engine shut-off while driving(These symptoms are also common in codes like the C0300 – Rear Prop Shaft Speed Sensor Issue, which may affect engine and drivetrain behavior.)
• Illuminated check engine light or ABS warning light
• No crank condition (engine won’t start)
• Reduced fuel efficiency
• Dashboard warning messages or error prompts
• Transmission shift issues or erratic gear changes
• All instrument cluster lights stay on simultaneously

These symptoms can severely affect your vehicle’s performance and safety. If you see the U0073 code displayed on your OBD2 scanner, it’s crucial to address the issue as soon as possible.

🔍 Diagnosing the U0073 Code

Properly diagnosing the U0073 trouble code requires a structured and methodical approach. Follow these steps for accurate diagnosis:

1. Check the Battery and Connections:
   Ensure the vehicle’s battery is fully charged. Inspect all battery terminals and electrical connectors for corrosion, looseness, or damage. Clean and tighten as necessary.
2. Use an OBD-II Scanner:
   Scan the vehicle using a reliable OBD-II diagnostic tool to retrieve stored Diagnostic Trouble Codes (DTCs). Compare the retrieved codes against the manufacturer’s specifications.
3. Scan All Modules on CAN Bus “A”:
   To confirm the issue, use a scan tool that can access all modules on CAN Bus “A”. Check if each module is communicating properly.
4. Inspect CAN Bus Communication:
   Verify the integrity of the communication between all control modules. Sometimes, a road test can help replicate the issue and reveal intermittent faults.
5. Component-Level Troubleshooting:
   Test individual components for failures. Use identical modules from the same vehicle type (same VIN) when comparing. The ECM (Engine Control Module) may need to be reprogrammed or replaced.
6. Clear the Code and Test Drive:
   After repairs, clear the DTCs using the scanner. Take the vehicle for a test drive to verify if the code reappears and ensure the system is functioning properly.

❌ Common Mistakes in Diagnosing the U0073 Code

Avoid these frequent errors when diagnosing communication issues related to U0073:

• Relying on only one scan tool or module to check for communication errors
• Using outdated or previously stored DTCs as reference without current verification
• Replacing or repairing parts without confirming compatibility via the manufacturer’s specification list
• Failing to notice or improperly reconnecting plugs and connectors
• Removing components without checking for communication faults on CAN Bus “A”
• Delaying diagnosis or ignoring minor symptoms
• Overlooking related sensors like the transmission speed sensor or oxygen (O2) sensor
• Skipping crucial steps such as voltage checks and resistance tests during diagnosis
• Ignoring analog gauge readings during component testing
• Randomly replacing parts without verifying the root cause(This is a common mistake also seen in diagnosis of U0002 Low-Speed CAN Bus Code — where rushed repairs often cause more harm than good.)

Always follow each diagnostic step thoroughly to avoid misdiagnosis and unnecessary repairs.

🔧 How to Fix Trouble Code U0073

Resolving the U0073 code involves targeted troubleshooting and may include the following steps:

• Replace faulty modules such as the PCM (Powertrain Control Module), ECM, or other affected units
• Repair or replace damaged CAN High/Low communication lines(To understand more complex CAN communication errors, also see our in-depth write-up on U0001 – High-Speed CAN Bus Communication Fault.)
• Re-flash the affected module if recommended by the manufacturer
• Replace malfunctioning sensors after verifying they impact communication
• Check and restore proper communication between all modules before clearing codes

⚠️ Why It’s Important to Fix the U0073 Code Immediately

The U0073 OBD-II code is a critical communication fault that can severely affect your vehicle’s performance. It disrupts signals between control modules, potentially leading to:

• Power loss
• Starting issues
• Dashboard warning light malfunctions
• Erratic transmission behavior
• Decreased fuel economy

Depending on the severity and affected module, repairs may cost anywhere from $100 to $1000. Prompt action can prevent further damage and help restore safe driving conditions.

More OBD2 Error Codes:
Explore related communication codes:
➡️ U0001 Code – High-Speed CAN Communication Bus
➡️ U0002 Code – Low-Speed CAN Communication Bus