In the complex world of modern vehicles, the Controller Area Network (CAN) bus system acts as the central nervous system, enabling various control modules to communicate and coordinate functions seamlessly. When your vehicle’s diagnostic system flags an EOBD/OBD-II error U0073, it indicates a disruption in this critical communication network, specifically on Bus “A”. As an automotive repair expert at autelfrance.com, I’m here to break down what this error means, its potential symptoms, causes, and how to approach diagnosis and repair.
What Does the U0073 Code Signify?
The OBD-II diagnostic trouble code U0073, technically described as “Control Module Communication Bus ‘A’ Off,” points to a malfunction within the vehicle’s communication circuit. This circuit, commonly known as the CAN bus, is essential for modules like the engine control unit (ECU), transmission control unit (TCU), anti-lock braking system (ABS), and others to exchange data. Without a properly functioning CAN bus, these modules can’t communicate effectively, leading to a range of drivability issues and potentially preventing your scan tool from connecting to the vehicle’s systems. It’s crucial to understand that U0073 specifically refers to Bus “A,” distinguishing it from similar codes like U0074, which pertains to Bus “B.”
Symptoms Associated with U0073 Error
When the U0073 code is triggered, you might observe several symptoms, signaling communication problems within your vehicle:
- Malfunction Indicator Lamp (MIL) illumination: The check engine light will likely be activated on your dashboard.
- Reduced Engine Power: The vehicle may experience a noticeable decrease in power and performance.
- Poor Fuel Economy: Inefficient communication can affect engine management, leading to increased fuel consumption.
- Illuminated Instrument Cluster Lights: You might see a cascade of warning lights on the instrument cluster, as various systems report communication failures.
- No-Crank or No-Start Condition: In severe cases, a complete communication breakdown can prevent the engine from starting.
Potential Causes of U0073
Several factors can lead to the U0073 error code. Pinpointing the exact cause is crucial for effective repair. Common culprits include:
- Open Circuit in CAN Bus + Wire: A break or disconnection in the positive wire of the CAN bus “A” circuit.
- Open Circuit in CAN Bus – Wire: Similarly, a fault in the negative wire of the CAN bus “A” circuit.
- Short to Power in CAN Bus Circuit: One of the CAN bus wires may be short-circuiting to a power source.
- Short to Ground in CAN Bus Circuit: Conversely, a CAN bus wire could be shorting to ground.
- Faulty Control Module (Rare): Although less frequent, a malfunctioning control module can sometimes disrupt CAN bus communication.
Diagnostic Steps and Repair Procedures for U0073
Diagnosing the U0073 error requires a systematic approach. Here’s a step-by-step guide to help you troubleshoot:
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Check for Technical Service Bulletins (TSBs): Always begin by checking for TSBs related to your vehicle’s make and model. Manufacturers often release bulletins addressing known issues, which can save you valuable diagnostic time. For instance, General Motors issued bulletin # 08-07-30-021E for many 2007-2010 GM vehicles regarding communication issues.
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Scan for Additional Diagnostic Trouble Codes (DTCs): Use an OBD-II scan tool to retrieve all stored DTCs. If you find other codes related to module communication, address those first. Misdiagnosing U0073 before resolving other communication-related codes is a common mistake.
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Visually Inspect Connectors and Wiring: Locate all CAN bus communication connections in your vehicle’s wiring diagrams. Once identified, carefully inspect the connectors and wiring for any signs of damage. Look for:
- Chafing or Rubbing: Wires rubbing against chassis components can wear through insulation.
- Bare Wires: Exposed wires increase the risk of shorts.
- Burn Spots or Melted Plastic: Indicating overheating or short circuits.
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Examine Connector Terminals: Disconnect the connectors and inspect the terminals inside. Look for:
- Corrosion: A buildup of oxidation, often appearing as white or powdery residue.
- Burning: Signs of heat damage or electrical arcing.
- Green Coloration: Often indicates copper corrosion.
If terminal cleaning is necessary, use an electrical contact cleaner or 91% isopropyl alcohol with a soft plastic bristle brush. Allow the terminals to air dry completely before applying dielectric silicone compound to ensure good contact and prevent future corrosion.
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Clear DTCs and Retest: If your scan tool can now communicate or if you resolved any module communication-related fault codes during the connector inspection, clear all DTCs and re-scan. If U0073 does not return, the issue likely stemmed from poor connections.
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Module Isolation (If Communication Remains Impossible): If communication is still not possible, or if U0073 persists, you can attempt to isolate the faulty module by disconnecting one control module at a time.
- Disconnect Negative Battery Cable: Always disconnect the negative battery cable before working on electrical components.
- Disconnect Module Connectors: Unplug the electrical connector(s) from a single control module.
- Reconnect Battery and Retest: Reconnect the negative battery cable and try to communicate with the scan tool again.
- Repeat for Each Module: If communication is still unsuccessful, repeat this process for each control module, one at a time.
If communication is restored or the codes clear after disconnecting a specific module, that module or its associated wiring is likely the source of the problem.
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Seek Professional Automotive Diagnostic Assistance: If you are unable to restore communication or pinpoint the fault after these steps, it’s advisable to consult a trained and experienced automotive diagnostician. Diagnosing CAN bus issues can be complex and may require specialized tools and knowledge.
Related DTC Discussions and Community Support
For further assistance and to engage with a community of automotive experts and enthusiasts, we encourage you to visit our FREE car repair forums. There, you can post specific questions about your U0073 code, share your diagnostic experiences, and benefit from the collective knowledge of the community.
Disclaimer: This information is for informational purposes only and should not be considered professional repair advice. We are not liable for any actions taken on your vehicle based on this information. Automotive repair should be performed by qualified technicians. Copyright protected content.
