U0402 is a generic communication/data integrity fault that flags when a control module receives vehicle network data it considers invalid or unusable. In SAE terms it is a network-level message failure rather than a guaranteed failed sensor or single module. The code says a message’s content, timing, or format failed plausibility checks inside the receiving unit. Interpretation can vary by make, model, and year, so you should treat U0402 as a symptom pointing you toward wiring, power/ground, or bus message issues until tests narrow the cause.
What Does U0402 Mean?
SAE J2012 defines DTC structure and some standardized descriptions; full digital annex entries are published in the SAE J2012-DA digital annex. U0402 is shown here without a hyphen Failure Type Byte (FTB). If an FTB were present (for example U0402-1A), it would act as a subtype identifying the specific failure mode or data element involved while the base U0402 still indicates an invalid or implausible message.
There is no single universal component-level definition for U0402 across all vehicles. The exact source and affected module can vary by make, model, and year. What distinguishes U0402 is that the receiving control unit detected invalid data content, timing, checksum, or format on a vehicle communication link — a protocol-level or plausibility failure rather than a straightforward open or short.
Quick Reference
- System: Vehicle network message invalid/implausible
- Common symptom: loss or degradation of functions that rely on the bad message
- First checks: power, ground, and connector integrity at nearby modules
- Important tests: bus voltage levels, message presence, and plausibility using a scope or scan tool
- Do not replace modules without confirming wiring and bus health
- Interpretation varies by vehicle; confirm with OEM data or module message mapping
Real-World Example / Field Notes
In the shop you’ll often see U0402 appear after events that disturb network signals: a recent battery disconnect, aftermarket radio installation, or collision repair that disturbed connectors. A common pattern is an intermittent U0402 tied to loose or corroded connector pins on a gateway or a module ground that moves the reference voltage enough to make message content fail plausibility checks. Another practical observation is that U0402 sometimes appears together with transient CAN bus errors when termination or shield integrity is poor; these are one possible cause, not a certainty.
Technicians also report cases where a sensor replacement or a module swap introduced wiring harness polarity or signal-level differences that downstream modules flagged as invalid — again commonly associated with poor connector mating, incorrect harness routing, or aftermarket devices placed on the bus. Always confirm message contents and bus voltages with a proper scan tool and oscilloscope before assuming an internal module fault.
Symptoms of U0402
- Fault Indicator MIL or warning light illuminated related to network message errors or general drivability warnings.
- Intermittent Behavior Periodic loss of certain vehicle functions that correlate with driving or ignition cycles.
- Reduced Function Limited operation of systems that rely on the missing message (may include powertrain or stability functions).
- Communication Errors Multiple network-related fault messages stored in scan tool memory or freeze frame data showing missing frames.
- Inconsistent Sensor Data Implausible or blank sensor readings on a dealer-level scanner or data logger for a subsystem.
Common Causes of U0402
Most Common Causes
- Wiring or connector faults between control modules and the vehicle data bus that prevent a required message from being received.
- Loss of sensor or module power/ground that stops a sending module from transmitting its message.
- Intermittent module reboot or software glitch in a transmitting module causing message dropout.
- High bus error rate on Controller Area Network (CAN) segments or gateway misroute preventing message propagation.
Less Common Causes
- Physical damage to the data bus (corrosion, chafing) or aftermarket devices introducing noise onto the network.
- Internal module processing or input-stage issue in the transmitting or gateway module — considered only after external tests pass.
- Faulty termination resistors or incorrect bus topology after previous repairs.
Diagnosis: Step-by-Step Guide
Tools: Digital multimeter (DMM), oscilloscope capable of CAN-level signals, manufacturer-capable scan tool with data and reflash functions, wiring/connector probe pins, backprobing leads, wiring diagrams or network map, fused jumper kit, and a logic/data logger. Also have basic hand tools and a known-good ground strap.
- Retrieve freeze frame and full DTC data with a capable scan tool; note message name, sending module, and any accompanying network faults. Export or photograph data for reference.
- Verify the code is shown without an FTB (no hyphen) or note the FTB subtype if present; record failure counts and conditions (key on, while driving, after start).
- Check obvious power and ground at the suspected sending module and gateway(s) using the DMM; confirm battery voltage at module connectors with key on and cranking conditions.
- Visually inspect wiring and connectors on related harness runs and gateway modules for corrosion, pin push-back, or water intrusion; gently wiggle harness with scanner monitoring to see if the message appears/disappears.
- Measure CAN bus voltages with DMM: static bias voltages (should be ~2.5 V nominal per CAN spec). Use an oscilloscope to look for proper differential waveform and absence of excessive noise or dominant timeouts.
- Isolate network segments if possible: logically disconnect non-essential modules or uses of service connectors to see if bus error rate drops and message returns. Re-check message presence after each change.
- Perform sensor plausibility checks on any inputs required by the sending module (voltage, frequency, resistance); compare to known-good values or manufacturer data using Mode $06 and live data streams.
- Replace or repair identified wiring/connector faults, then clear codes and perform a drive cycle while monitoring live data for reappearance. If wiring and power/ground test good but message still missing, test for gateway routing using network map and selective module wake-up tests.
- If all external inputs, power, ground, wiring, and bus integrity test good, consider advanced module-level diagnostics: log continuous data, attempt reflash or dealer-level diagnostics, and only then evaluate possible internal processing or input-stage issue in the transmitting module.
Professional tip: Always confirm repair decisions with reproducible measurements—document the exact test that showed the fault (e.g., oscilloscope capture of missing differential frames or voltage drop under load). Replace modules only after verifying wiring, power/ground, and bus integrity; a clear “message present” trace after repair proves success.
Possible Fixes & Repair Costs
Low-cost fixes address wiring, connectors, and power/ground issues identified by testing. If continuity or voltage tests show an intermittent splice or corroded connector, repair and re-test. Typical repairs include connector cleaning, crimp replacement, or pin repair when open/short conditions are found. If a specific sensor or module input is proven implausible but wiring and power/ground check good, the next step may be module input-stage repair or replacement after confirmation.
- Low: $50–$200 — justified when tests show connector corrosion, loose terminal, or simple splice repair and the module reports normal operation after repair.
- Typical: $200–$800 — justified when a harness section must be replaced, multiple connectors need work, or a replaceable sensor/module is diagnosed as the source after wiring and power/ground pass.
- High: $800–$2,000+ — justified when a control module replacement and subsequent programming are required after exhaustive external input and network tests confirm an internal processing or input-stage issue.
Factors affecting cost: labor rates, accessibility, required programming, and whether the fault is intermittent (which increases diagnosis time). Always document failing test results—voltage, continuity, resistance, and CAN/LIN message captures—before replacing major components. Replace modules only after all external wiring, grounds, power rails, and bus communication tests pass.
Can I Still Drive With U0402?
You can often drive short distances with a U0402 present, but it depends on the function of the invalid message. U0402 indicates one networked message or sensor data was reported as invalid; safety systems that rely on that data may be degraded or in fallback mode. Check plausibility of related vehicle systems and avoid prolonged driving if steering, braking, or stability systems report reduced performance. Run basic checks and drive cautiously to a repair facility.
What Happens If You Ignore U0402?
Ignoring U0402 can leave a subsystem operating with degraded or fallback data, potentially reducing safety or responsiveness. Over time, intermittent faults may worsen, connectors corrode further, or secondary modules may set additional related faults. Prompt basic testing reduces risk and diagnostic 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
- U0402 is a network-level invalid data message affecting chassis-related systems.
- Diagnosis is test-driven: verify power, ground, wiring, and bus messages before replacing modules.
- Costs range widely depending on whether the fix is wiring, sensor replacement, or module replacement.
Vehicles Commonly Affected by U0402
U0402 is commonly seen on modern vehicles from manufacturers with complex chassis networks, often reported on Ford, General Motors, and Toyota platforms. These manufacturers frequently use multiple networked control modules and sensors; increased network complexity and distributed sensor architectures make invalid-message faults more likely to be logged. Interpretation and exact affected module can vary by model year and option package—confirm with vehicle-specific network tests.
FAQ
Can I clear U0402 and hope it stays away?
Clearing the code will remove the stored trouble code, but it does not fix the underlying cause. If the condition is intermittent you may temporarily regain normal operation, but the fault will likely return if wiring or a module input is still failing. Use clear-and-drive only as a test step, then perform power/ground checks and capture CAN frames or Mode $06 data to verify the issue is resolved before declaring the repair complete.
Can U0402 cause ABS or stability systems to behave badly?
Yes—if the invalid message carries data used by anti-lock brake or stability control systems, those systems may enter reduced-function or failsafe modes. Severity depends on which message was invalid and how the vehicle’s control strategy handles missing or implausible data. Prioritize plausibility checks, wiring tests, and bus communication captures to confirm whether ABS/ESC inputs are receiving valid messages before changing major components.
Is module replacement usually required for U0402?
Module replacement is not usually the first step. Replace a module only after all external inputs—power, ground, sensor signals, connector integrity, and network messages—test good and you can reproduce an internal processing fault. Frame module failure as a last-resort diagnosis: “possible internal processing or input-stage issue” after external tests pass and message captures indicate the module is not transmitting or validating data correctly.
How long does diagnosing U0402 typically take?
Diagnosis time varies widely: simple connector or harness repairs may take under an hour, while intermittent network faults can take several hours. Expect 1–4 hours for a systematic, test-driven approach: verify voltages and grounds, continuity checks, inspect connectors, and capture bus traffic with a scan tool or scope. Intermittent problems require extended road testing and data logging to recreate the failure.
What tests confirm wiring vs module problems for U0402?
Start with battery voltage and ground integrity, then continuity and resistance checks on suspect circuits. Inspect and wiggle connectors while watching live data and CAN/LIN frames with a capable scan tool. Use a scope to check signal waveforms where applicable. If power/ground, wiring continuity, and bus messages are all good yet the module sends invalid data, that supports an internal module issue—only then consider module repair or replacement.