U0073 – Control Module Communication Bus Off means a major control module has removed itself from the CAN network because it cannot maintain proper communication. When a module goes “bus off,” it stops participating in the data stream to prevent further network disruption. This can disable key systems like the engine, transmission, ABS, or steering. You may experience warning lights, stalling, power steering loss, or no-start conditions. This guide explains what U0073 means, its symptoms, causes, step-by-step diagnostics, and the most effective repair options.
What Does U0073 Mean?
U0073 is a generic OBD-II code that indicates a control module has exceeded communication error limits and entered a “bus off” state. In this mode, the module disconnects itself from the CAN bus to avoid corrupting network data. This typically occurs when there are wiring faults, voltage issues, or other modules flooding the network with bad messages.
Once a module enters bus-off, it stops communicating entirely. The vehicle may lose critical functions, depending on which module goes offline. Because CAN communication is essential for modern vehicles, U0073 should be diagnosed quickly to prevent further failures.
Quick Reference
- OBD-II Family: U-Code (Network Communication)
- Scope: Generic
- System: CAN Bus / Control Module Network
- Difficulty Level: Advanced
- Estimated Repair Cost: €100–€650+
- Last Updated: 20 November 2025
Real-World Example / Field Notes
A crossover SUV arrived with ABS, traction control, and power steering lights illuminated. Live data showed no communication with the ABS module. The PCM and BCM both stored U0073. Further testing revealed the ABS module had entered bus-off due to excessive CAN errors caused by a partially shorted wire near the wheel well. Repairing the wiring immediately brought the module back online.
Another case involved a vehicle that stalled randomly. The PCM occasionally entered bus-off because a failing alternator created voltage spikes, corrupting CAN messages. After replacing the alternator, no further U0073 events occurred.
Symptoms of U0073 – Control Module Communication Bus Off
- Multiple warning lights: ABS, traction control, EPS, airbag, or check engine.
- Intermittent or total no-start: PCM may drop offline.
- Loss of power steering assist: If EPS module goes bus-off.
- Stalling or hesitation: PCM communication interrupted.
- No communication with one or more modules: Scan tool shows “No Response.”
- Cluster freezing or dropping out: IPC may lose CAN data.
- Transmission limp mode: TCM loses engine data stream.
Common Causes of U0073
Most Common Causes
- Wiring faults causing excessive CAN errors
- Short-to-power or short-to-ground on CAN-H or CAN-L
- Failed module overwhelming the network with bad data
- Corroded connectors or water intrusion
- Weak battery or alternator voltage spikes causing instability
Less Common Causes
- Internal module transceiver failure
- Poor grounding affecting module communication
- Aftermarket alarms, trackers, or audio equipment interfering with CAN
- Rodent damage exposing CAN wiring
- Failed terminating resistor reducing network stability
Diagnosis: Step-by-Step Guide
U0073 requires systematic diagnosis to identify the module that went bus-off and determine why the network is unstable. Follow these steps carefully.
Tools You’ll Need
Advanced scan tool, multimeter, oscilloscope (recommended), wiring diagrams, CAN breakout box, backprobe kit, test light, and charging system tester.
- Identify which module is bus-off: Use a scan tool to find the module reporting no communication or repeated errors.
- Check charging system: Test for low voltage or alternator ripple. Bad charging systems can force modules into bus-off.
- Inspect wiring visually: Look for crushed, corroded, melted, or wet harness areas, especially near wheel wells and footwells.
- Measure CAN-H and CAN-L voltages: CAN-H ~3.5V, CAN-L ~1.5V. Abnormal readings indicate wiring or module faults.
- Test resistance across CAN-H and CAN-L: With ignition off, expect ~60 ohms. Values outside range suggest wiring faults.
- Check connectors for corrosion: Dirty or wet terminals cause CAN errors that lead to bus-off events.
- Unplug modules one at a time: If the network stabilizes after unplugging a module, that module may be failing.
- Perform continuity checks: Look for shorts or opens along CAN wiring paths.
- Use oscilloscope: Check for distorted waveforms, noise, or missing differential activity.
- Test grounds: Verify engine, chassis, and module grounds are clean and tight.
Pro Tip: A faulty module that repeatedly goes bus-off often overheats internally. If a module comes back online only after cooling down, suspect internal transceiver failure.
Possible Fixes & Repair Costs
- Repair damaged CAN wiring: €60–€200
- Replace corroded connectors: €20–€100
- Fix water intrusion sources: €80–€250
- Replace failing control module: €150–€650+
- Repair or replace damaged harness sections: €150–€400
- Replace faulty alternator or battery: €120–€400
Can I Still Drive With U0073?
Driving with U0073 is risky. A bus-off module may disable critical systems like ABS, EPS, or engine control. You may lose power steering, experience stalling, or have no-start events. If multiple warning lights are on or the vehicle behaves unpredictably, do not continue driving until repairs are made.
Related Codes
- U0009 – High Speed CAN Communication Bus (-) Shorted to Bus (+)
- U0008 – High Speed CAN Communication Bus (-) High
- U0007 – High Speed CAN Communication Bus (-) Low
- U0006 – High Speed CAN Communication Bus (-) Open
- U0005 – High Speed CAN Communication Bus (+) High
- U0004 – High Speed CAN Communication Bus (+) Low
- U0003 – High Speed CAN Communication Bus (+) Open
- U0002 – High Speed CAN Communication Bus Performance
- U0001 – High Speed CAN Communication Bus
Key Takeaways
- U0073 means a module has disconnected itself from the network due to severe CAN errors.
- Wiring faults, voltage instability, or a bad module commonly cause bus-off events.
- Small wiring issues can create major network instability.
- Driving may be unsafe depending on the module affected.
FAQ
What does “bus off” actually mean?
It means a module has exceeded communication error limits and stops transmitting to avoid corrupting the network.
Can low voltage trigger U0073?
Yes. Weak batteries and charging system faults often cause CAN errors that force modules into bus-off mode.
Is U0073 dangerous?
It can be. Loss of ABS, steering assist, or engine communication may occur. Avoid driving if symptoms are severe.
Does U0073 always mean a bad module?
No. Most cases are wiring or voltage related, but a defective module can also cause bus-off errors.
Should I replace the module immediately?
Only after verifying wiring integrity, proper voltage, and CAN bus stability. Many modules go bus-off due to external faults.