You’ve pulled a U0406 and the vehicle’s network is reporting an invalid or unexpected message from a module on the vehicle data bus. This is a network-level fault: an ECU (Electronic Control Unit) received data that failed plausibility, format, or source checks. Interpretation varies by make, model, and year, so you must confirm with tests. Focus your work on wiring and connectors, power and ground integrity, sensor plausibility, and Controller Area Network (CAN) or Local Interconnect Network (LIN) message checks. Diagnose by measuring signals and verifying message sources before replacing modules.
What Does U0406 Mean?
SAE J2012 defines the Diagnostic Trouble Code structure and assigns U-codes to vehicle network communication issues. This article follows SAE J2012 formatting and references the SAE J2012-DA digital annex where standardized DTC descriptions are published. U0406 is a network message fault indicating an invalid or unexpected message content or source was received by an ECU. The code as shown here does not include a hyphen suffix (Failure Type Byte, FTB).
An FTB, when present (for example U0406-1A), narrows the failure subtype—such as specific message format, checksum, timing, or source mismatch—according to manufacturer definitions. There is no single universal component-level meaning for U0406 across all makes and models; interpretation commonly varies. Confirm the root cause with electrical checks (power/ground), connector/wiring inspection, and network message capture before concluding a module-level failure.
Quick Reference
- System: Network message invalid or implausible on vehicle data bus
- Primary checks: power, ground, and connector integrity at affected modules
- Network checks: verify CAN/LIN physical layer, termination, and message traffic
- Tools: scan tool with CAN data, oscilloscope or CAN bus analyzer, DVOM
- Diagnosis tip: confirm message source and plausibility with live data before replacing control units
Real-World Example / Field Notes
In the shop, U0406 often appears after intermittent wiring faults, a loose connector at a dash harness, or after a collision that disturbed ground straps. Technicians commonly associated this fault with a cluster or gateway message failing plausibility checks, but that is one possible cause—not a confirmation. A quick scan tool check can show which message ID or source parameter is flagged; use that to focus wiring and connector inspection.
Field testing frequently reveals marginal voltage or poor ground return at the instrument area causing corrupt message frames. Another common pattern is a shorted or noisy sensor signal feeding a broadcast message; the ECU relays implausible values and a receiving module sets U0406. Use a CAN bus analyzer to capture frame timing, CRC, and sender node behavior. If the physical layer and power/ground test clean, proceed to controlled substitution or module bench-testing per manufacturer guidance.
Symptoms of U0406
- Warning Lamp – An illuminated vehicle stability or general fault indicator on the dash.
- Stability Intervention – Unexpected traction or stability control intervention or reduced functionality.
- Loss of Assist – Altered steering feel or degraded steering assist behavior reported by the driver.
- Network Errors – Multiple communication-related messages or a persistent communication fault on a scan tool.
- Inconsistent Readings – Sensor values shown on a scan tool jump, freeze, or disagree with expected vehicle motion.
- Battery/Start Issues – Erratic module wake-up or startup symptoms related to control modules on the same network.
Common Causes of U0406
Most Common Causes
- Interrupted or corroded wiring and connectors on the network or the sensor circuit, commonly associated with poor contact or water ingress.
- Controller Area Network (CAN) message invalid or corrupted due to intermittent bus wiring faults or connectors that alter bus impedance.
- Sensor plausibility failure where the received message values do not match other vehicle motion data, commonly associated with an out-of-range sensor signal.
- Power or ground fault to the sensor or control module input stage causing unreliable or missing messages.
Less Common Causes
- Module internal processing or input-stage issue after external wiring, power, ground, and network checks pass.
- Interference from aftermarket equipment or incorrect module programming that changes message formatting.
- Rare intermittent mechanical damage to the sensor or connector that only appears under vibration or temperature change.
Diagnosis: Step-by-Step Guide
Tools: diagnostic scan tool with CAN data and logging, multimeter, oscilloscope or CAN bus analyzer, backprobe pins, wiring diagrams, terminal cleaner, jumper wires, insulated hand tools.
- Connect a capable scan tool and read freeze frame and live data. Note whether the fault is shown with an FTB (failure type byte) or without; record message frequency and apparent source.
- Use the tool’s data list or bus monitor to identify whether the expected message ID is present and whether payload values are plausible compared with vehicle speed and yaw rate.
- Check for related network errors: perform a CAN bus health check with an oscilloscope or CAN analyzer to verify proper recessive/dominant voltages and bus bit timing.
- Visually inspect and flex wiring and connectors for the sensor and nearby modules; look for corrosion, bent pins, or water intrusion that commonly causes intermittent faults.
- Verify power and ground at the sensor connector with a multimeter while key on; confirm stable battery voltage and low-resistance ground reference under load.
- Backprobe the signal line and capture waveform with an oscilloscope while exercising the sensor or driving slowly; check for noise, missing frames, or level shifts indicating wiring or transceiver issues.
- If signals and bus look good but messages remain invalid, compare the suspect message against other vehicle sensors for plausibility and check On-board diagnostics (OBD) Mode $06 data where available.
- Swap to a known-good connector or harness segment only after verifying wiring diagrams; do not assume a module swap—only consider module replacement after all external tests pass.
- Clear codes and perform a drive cycle while logging bus traffic to confirm the fault reproduces and verify the repair by the absence of the code and restoration of valid messages.
Professional tip: Always confirm a wiring or connector repair by probing live bus waveforms and re-running a logged drive cycle—module replacement is a last step after external inputs test good.
Possible Fixes & Repair Costs
Low: $50–$150 — Typical fixes in this range include connector cleaning, reseating a loose plug, or clearing a spurious fault after confirming signal plausibility with a scan tool. Justify by finding corroded pins, intermittent connector contact with wiggle testing, or transient bus errors logged only once.
Typical: $150–$600 — Common repairs are repairing damaged wiring or replacing a sensor harness, repairing a short to battery/ground, or replacing a junction connector. These are justified when you measure incorrect voltages, open circuits, or consistent CAN/LIN error frames on the bus during scope or multimeter checks.
High: $600–$1,800 — Higher costs cover replacing or programming a control module (possible internal processing or input-stage issue) only after all external wiring, power, ground and network checks pass. Also includes extensive wire loom replacement or labor-intensive chassis harness repairs. Justify module work with bench traces, good input power/grounds, verified network activity, and persistent invalid message counts in the module’s freeze/frame or mode $06 data.
Factors affecting cost include labor time, access difficulty, OEM part price, whether programming is required, and whether the fault is intermittent (needs longer diagnostic time). Always document network message timing and scope captures before ordering parts.
Can I Still Drive With U0406?
You can often drive with U0406, but whether it’s safe depends on what subsystem supplied the invalid message. If the invalid message affects anti-lock braking or stability control, those features may be reduced or disabled. Drive cautiously: verify system functionality (ABS, traction control) by low-speed tests in a safe area. If the fault is limited to an informational module, drivability may be unaffected. Get electrical and network checks as soon as practical.
What Happens If You Ignore U0406?
Ignoring the code can lead to loss of safety features, false warnings, or cascading faults on shared vehicle networks. Intermittent network errors left unaddressed may become harder to diagnose and could mask other impending failures or degrade system performance over time.
Related Codes
- U0419 – Invalid Data Received From Steering Effort Control Module
- U0418 – Invalid Data Received From Brake System Control Module
- U0417 – Invalid Data Received From Park Brake Control Module
- U0416 – Invalid Data Received From Vehicle Dynamics Control Module
- U0414 – Invalid Data Received From Four-Wheel Drive Clutch Control Module
- U0413 – Invalid Data Received From Battery Energy Control Module B
- U0412 – Invalid Data Received From Battery Energy Control Module A
- U0411 – Invalid Data Received From Drive Motor Control Module
- U0409 – Invalid Data Received From Alternative Fuel Control Module
- U0408 – Invalid Data Received From Throttle Actuator Control Module
Key Takeaways
- U0406 signals an invalid network message related to chassis/brake data, not a guaranteed failed part.
- Interpretation varies by make/model; confirm with electrical and network testing.
- Prioritize wiring, connectors, power/ground, and CAN/LIN message checks before module replacement.
- Costs range widely; justify every repair with measured test results and scope captures.
Vehicles Commonly Affected by U0406
U0406 is commonly seen on modern vehicles from manufacturers with distributed networked control architectures, often reported on Ford, General Motors, and Toyota models. These platforms use multiple electronic control units that share brake and chassis data across CAN networks, increasing the chance that a single invalid message is logged when wiring, a connector, or a module input behaves inconsistently. Frequency depends on network complexity and vehicle age.
FAQ
Can I clear U0406 and ignore it if the light goes away?
Clearing the code is a temporary step to see if the fault returns, but it does not diagnose the root cause. If the code returns, collect live data and perform network error logging and scope captures while recreating the condition. If it does not return, monitor the vehicle; intermittent errors often need longer road tests or replicated electrical environment checks before declaring the issue resolved.
Can a weak battery cause U0406?
Yes — low or unstable battery voltage can create corrupt messages or cause modules to misbehave on the network. Verify stable battery voltage and good charging system output first. Perform voltage drop tests on power and ground feeds to the affected control modules and watch for CAN/LIN error frames during voltage fluctuation. If voltage normalizes and the fault clears, further investigation into power distribution is warranted.
Is replacing the control module usually required for U0406?
No — module replacement is not the first step. Only consider a possible internal processing or input-stage issue after you verify wiring, connectors, power, ground, and network traffic are all within specifications. Use scope traces, bus error counters, and bench tests where possible. Replace the module only when testing proves external causes are eliminated and the module still produces invalid message outputs.
How do technicians confirm which node sent the invalid message?
Technicians use a combination of scan tool message tracing, module freeze frames or mode $06 data, and CAN/LIN bus traffic captures with a scope or diagnostic logger. Correlate timestamps, message IDs, and error counters. Then perform voltage and continuity checks on that node’s power, ground, and network wiring. Replace or repair components only after confirming message source and ruling out wiring or connector faults.
How long will a professional diagnosis and repair typically take?
Diagnosis time varies: simple connector or wiring repairs can be under an hour, while intermittent network faults or harness replacements may take several hours. If module replacement and programming are required after thorough testing, expect additional shop time. Technicians should quote time based on initial test results; intermittent issues often require extended road tests to reproduce and confirm repair effectiveness.