U0404 is a network-level diagnostic signal indicating that a control module logged receipt of invalid or implausible data from another module on the vehicle communication bus. As a system-level notice, it points to an information integrity or plausibility problem on a networked circuit rather than proving a single failed sensor or a fixed component. Interpretation often varies by make, model, and year; you should confirm the source with basic electrical checks and bus-level testing such as power/ground verification, voltage measurements, and CAN (Controller Area Network) message capture to locate where bad data originates.
What Does U0404 Mean?
Under SAE J2012 formatting, U0404 is classified as a network communication condition that records invalid data received by one module from another. SAE J2012 defines the structure of DTCs and some standardized descriptions; the SAE J2012-DA digital annex publishes the formal DTC text used as a baseline for many manufacturers. This article follows those conventions while recognizing that module-level interpretations can differ between OEMs.
The code shown here is presented without a hyphen suffix Failure Type Byte (FTB). An FTB, when present, refines the base code by indicating a subtype or failure-mode detail (for example timing, checksum, or plausibility variants). U0404 specifically flags data integrity/plausibility—meaning a message failed expected format, checksum, timing, or value plausibility checks—rather than a raw open or short electrical classification. Exact module names or signal sources can vary by vehicle and must be confirmed by testing.
Quick Reference
- System: Network data integrity / message plausibility
- Typical symptom: Warning lights, degraded functions, or intermittent behavior
- Initial checks: Scan for active/recorded faults and note freeze-frame or timestamped events
- Key tests: Power/ground, CAN bus voltage, message capture, and wiring connector inspection
- Common causes: Intermittent wiring/connectors, module message corruption, or bus interference
- Repair approach: Test, verify, then repair wiring or replace module only after external inputs test good
Real-World Example / Field Notes
In the workshop, U0404 often shows as an intermittent logged event tied to a feature that stopped responding after a recent repair or collision. Technicians commonly associated that symptom with chafed harnesses near suspension or steering components where movement stresses wires. In one case, a rubbed CAN pair at a frame mounting point produced CRC or checksum failures that a receiving module flagged as invalid data.
Another frequent observation is connector contamination—corrosion or moisture at a multi-pin connector can intermittently corrupt messages. Technician practice: do a wiggle test of suspect harnesses while monitoring live CAN frames; loss, garbled IDs, or sudden value jumps on the bus often point to wiring or connector faults rather than the receiving module itself. Remember to treat modules as suspect only after power, ground, wiring, and message integrity are confirmed good.
Focus on wiring, power/ground, and message plausibility checks when tracking a U0404 Network Message Invalid Data condition. Treat U0404 as a Controller Area Network (CAN) or other vehicle-network message that the receiving module flagged as invalid or inconsistent; it does not universally point to one failed actuator or sensor. Interpretation can vary by make, model, and year, so always confirm with electrical and network testing rather than assuming a single failed part.
Symptoms of U0404
- Warning lamp A related system warning or indicator illuminates on the dash when the network message is rejected.
- Loss of function Intermittent or complete loss of the subsystem controlled by the sender/receiver module.
- Erratic behavior Unexpected or inconsistent operation of features tied to the affected message.
- Stored freeze-frame Freeze-frame or snapshot data in the scan tool showing timing or message anomalies.
- Communication faults Additional network message timeouts or intermittent network errors reported by the scan tool.
- Multiple modules Two or more modules report symptoms that correlate with missing or invalid data on the bus.
Common Causes of U0404
Most Common Causes
- Intermittent wiring/connectors between the message originator and the network—corrosion, loose terminals, or damaged insulation commonly cause invalid payloads.
- Supply or ground instability at the sending or receiving module causing corrupted message content or timing irregularities.
- Bus-level issues on Controller Area Network (CAN) or LIN (Local Interconnect Network) such as improper termination, noise, or missing recessive/dominant levels.
- Software mismatch or calibration differences between modules creating unexpected or out-of-range message content (varies by vehicle).
Less Common Causes
- Intermittent sensor or actuator producing implausible data that the sender forwards, making the payload invalid to the receiver.
- Aftermarket modules or accessories that inject nonstandard messages or overload the bus.
- Poorly shielded wiring routed near strong electromagnetic sources causing bit errors on the network.
Diagnosis: Step-by-Step Guide
Tools: OBD‑II scan tool with CAN/LIN capability, digital multimeter, lab-quality oscilloscope, breakout box or data‑logger, backprobe set, wiring probe/LED, insulated jumper leads, wiring diagrams or service data.
- Connect a capable scan tool and confirm U0404 is active or stored; note freeze‑frame and any appended Failure Type Byte (FTB) if present.
- Observe live data and module message lists to identify which module sent or expected the invalid message; record message frequency and timing.
- Perform a quick battery voltage and key‑on voltage stability check while exercising the affected system to rule out supply collapse.
- Inspect and wiggle related connectors and wiring harnesses while watching live data for changes or disappearance of the message to catch intermittent faults.
- Backprobe the module power and ground with a multimeter to verify solid supply and ground under load; weak grounds often corrupt message processing.
- Use an oscilloscope at the CAN high and CAN low pins to check for proper differential signaling, bit errors, and correct idle levels; look for excessive noise or missing recessive/dominant states.
- Measure bus termination resistance across CAN high/low with the system power off to verify the expected combined termination (compare with service data or known-good vehicle when available).
- If bus signals and wiring test good, capture the message payload and compare its contents or checksum plausibility against known-good patterns or Mode $06/UDS data where applicable.
- Isolate suspect module by temporarily disconnecting non-critical nodes or peripherals (when safe) to see if the invalid message clears; only disconnect following safe service procedures and with the vehicle off where required.
Professional tip: Always confirm a suspected module failure only after exhaustive wiring, power/ground, and bus-signal testing. Capture oscilloscope traces of both a known-good vehicle (if available) and the problem unit; matching timing and amplitude supports or refutes an internal processing issue versus an external wiring or noise problem.
Possible Fixes & Repair Costs
Low: $50–$200 — This covers basic shop labor and parts for connector cleaning, dielectric grease, and reseating plugs. Justified when visual inspection shows corrosion, loose terminal engagement, or a single loose connector and a voltage/pulsing check shows intermittent contact. Typical: $200–$700 — Includes targeted wiring repair, pigtail replacement, or replacement of a sensor/module input harness. Use this when continuity, wiggle, or resistance tests reveal damaged conductors or intermittent opens/shorts in the harness. High: $700–$2,000+ — Covers replacement of an electronic control unit or major wiring harness sections and higher labor associated with dashboard removal or module programming. Pursue this only after all external checks (power, ground, signal, harness continuity, and network integrity) pass and the fault persists, indicating possible internal processing or input-stage issue.
Costs vary by labor rates, accessibility, and whether dealer-level programming is required. Always justify any replacement with concrete test evidence: failing continuity, abnormal voltage at a pin, persistently invalid CAN frames on a network sniffer, or replicated fault with known-good wiring. If a module replacement is considered, confirm wiring, connectors, and power/ground are within specification first; then document failing Mode $06 or freeze-frame data that isolates the module’s inputs as good before spending on a module.
Can I Still Drive With U0404?
You can often drive with U0404 present, but risk depends on which vehicle functions rely on the missing or invalid message. Some systems degrade to a limp or reduced-function mode, while others continue working normally. Check for related warnings on the dash and test affected systems for plausibility before deciding to drive long distances. If critical safety systems appear degraded or intermittent, avoid driving and address the network wiring or module communication fault promptly.
What Happens If You Ignore U0404?
Ignoring the code can allow intermittent or progressive loss of vehicle features that depend on the missing message, and may mask a developing wiring fault that becomes permanent. You could face unexpected behavior in linked systems and possibly a failed inspection if communications-related safety lamp strategies are active.
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
- SAE structure: U0404 is a network message/data invalidation condition per SAE J2012-DA; interpretation varies by vehicle.
- Test-first approach: Verify power, ground, connector integrity, and wiring continuity before replacing modules.
- Network checks matter: CAN/LIN message traces and voltage waveform checks are often required to confirm invalid data source.
- Module caution: Consider internal module issues only after all external inputs test good.
- Cost drivers: Accessibility, required programming, and extent of wiring repair determine repair cost.
Vehicles Commonly Affected by U0404
U0404 is commonly seen on vehicles from manufacturers with complex serial networks and multiple control modules, such as Ford, General Motors, and BMW. These platforms often have many interdependent controllers and high network traffic, so an invalid message can appear more frequently. The exact meaning and which module reports the fault vary by make, model, and year; confirm with OEM wiring and in-vehicle network diagnostics.
FAQ
Can I clear U0404 and hope it won’t return?
Clearing the code may temporarily extinguish the warning, but it does not diagnose the root cause. If the underlying wiring fault, connector corrosion, or intermittent message condition remains, the code will likely return. Use clearing as a first step only after a visual and electrical plausibility check; if the fault reappears, proceed with the diagnostic steps that verify power/ground, wiring continuity, and bus message integrity.
Is module replacement usually required to fix U0404?
Module replacement is not the default solution. Technicians should exhaustively test wiring, connectors, power, and ground, and verify network messaging first. Only after all external inputs and the bus are proven good — and the module still reports invalid data with consistent Mode $06 or freeze-frame evidence — should a module be considered as a possible internal processing or input-stage issue. This prevents unnecessary high-cost replacements.
Can a bad ground or battery issue cause U0404?
Yes. Poor grounds or unstable supply voltage can cause modules to send invalid or corrupted messages, triggering U0404. Measure battery voltage under load, check module supply pins for stable voltage, and confirm chassis and engine-block grounds for low resistance. If voltage or ground tests are out of tolerance or fluctuate during wiggle tests, repair those items first and then re-evaluate the network message validity.
How will a tech confirm whether the message is coming from wiring or a module?
A technician will perform supply and ground voltage checks, pin-back probing for signal levels, continuity and resistance measurements, and wiggle tests while monitoring the network with a scope or CAN/LIN bus tool. Replicating the fault with a known-good harness or by substituting a known-good module (where practical) helps isolate the source. Only after external inputs test good is module internal failure considered.
What should I tell my repair shop when I bring a car with U0404?
Provide the exact code, any symptoms, when it appeared, and recent events (water exposure, battery disconnect, aftermarket installs). Mention any intermittent electrical issues or recent repairs. Ask the shop to perform power/ground checks, connector inspections, and a network trace before replacing modules. This helps ensure a test-driven diagnosis and avoids unnecessary part charges.