U0401 A module received invalid data from the engine or powertrain computer

Invalid data received from ECM/PCM "A"

Severity not verified — if the car runs badly, have it inspected

How serious U0401 is depends on which module stored it: bulletins range from a blind-spot fault to a lack of power, so we have not set one class.

It gets more serious if:

  • Inspect soon: Get it checked soon if U0401 comes with a lack of power, a transmission that will not shift properly, or a check engine light. Mazda bulletins report lack of power with U0401, and Honda's manual says a steady check engine light needs prompt inspection.

Source: how we rate severity

U0401 in short

U0401 means a module received data from the engine computer that did not make sense. The engine computer is still talking, but a value it sent was out of range or flagged as faulty, often because of another fault or software. How urgent it is depends on which module stored it and what else is set.

Unlike a lost-communication code, U0401 means messages are arriving but one of them is invalid. The engine computer may be passing on a bad sensor reading, flagging its own fault, or sending a value the receiving module does not accept.

Because of this, U0401 is often a symptom of another code. On Mazdas it comes with P061B when cranking is interrupted, and ALLDATA describes a 2014 Fusion where a damaged wheel speed sensor connector set U0401 in several modules.

The module that stored the code tells you what is affected: Ford's 2013-2014 Fusion and MKZ stored it in the blind-spot modules, Mazda's 2019 Mazda3 shows a driver-support warning, and Ford's 2015-2017 F-150 stored it in the front controls module.

Most likely causes

  1. Another fault the engine computer is reporting (a sensor or internal code)

    Common general cause
    Why it ranks here
    The data is invalid because something upstream is wrong. ALLDATA's Fusion case traced U0401 to a damaged wheel speed sensor connector, and Mazda's bulletin pairs U0401 with P061B.
    What would change this
    Rises if other P or C codes are stored with U0401. Falls if U0401 is the only code in every module.

  2. Module software that needs an update

    Supported by vehicle data
    Why it ranks here
    Ford's 2020 Escape message points to software for U0100/U0401, and Ford and Mazda have bulletins for U0401 in the blind-spot and driver-support modules.
    What would change this
    Rises if a dealer finds an update for your VIN. Falls if every module is already at the latest software.

  3. Network wiring, connector, or low battery voltage corrupting messages

    Possible — needs testing
    Why it ranks here
    Wiring and power faults are the most common network problems in general, but for U0401 specifically the bulletins point more often to other faults and software.
    What would change this
    Rises if U0401 comes with lost-communication codes or the battery is weak. Falls if bus resistance and voltage are normal.

What to test first

Start at step 1. Each result tells you what it means and where to go next.

  1. Scan all modules and note which module stored U0401 and every other code present.

    Low riskTool: scan tool that reads all modules

  2. Ask a dealer whether your VIN has a bulletin or update for U0401 in the module that stored it.

    Low risk

  3. Test the battery and check the network resistance and connectors at the engine computer.

    Use cautionTool: multimeter, battery tester

    Warning:Do not probe connectors with the ignition on, and avoid yellow airbag connectors. Let a shop do it if unsure.

Symptoms

  • Check engine light
  • "Safety and Driver Support Systems Partially Disabled" or a blind-spot warning
  • A/C, radio or window switches not working on some trucks
  • Lack of power or a transmission that will not shift past a gear Gets more serious: stop and have it checked.

How to fix

  1. Write down every code from every module, then diagnose any engine or sensor codes before chasing U0401.

  2. Ask a dealer whether your VIN has an open bulletin or software update.

  3. Have the battery tested if the code appeared after a slow crank or a flat battery.

On your vehicle

Mazda

  • 2018–2019 · CX-5

    Supported by vehicle data

    Mazda 01-015-18 links U0401 with P061B and a lack of power when engine cranking is interrupted (also CX-3, Mazda6, MX-5). Whether the bulletin is still current is not verified.

  • 2019 · Mazda3

    Supported by vehicle data

    Mazda SA-008-20: "Safety and Driver Support Systems Partially Disabled" with U0401:68. Whether the bulletin is still current is not verified.

  • 01-015-18-3513aStatus unverified

    Lack of power, check engine light, P061B:00 and U0401:00

    2018–2019cx-3, cx-5, mazda6, mx-5 · issued · NHTSA 10148004

    Covers lack of power and the check engine light with P061B and U0401 stored when engine cranking is interrupted.

    We couldn't confirm whether this bulletin is still current, so it doesn't count as confirmation.

  • SA-008-20Status unverified

    Safety and Driver Support Systems Partially Disabled with U0401:68

    2019mazda3 · issued · NHTSA 10170828

    Service alert for the warning message with U0401:68 stored.

    We couldn't confirm whether this bulletin is still current, so it doesn't count as confirmation.

Ford

  • 2013–2014 · Fusion

    Supported by vehicle data

    Ford ASI-44656: blind-spot and cross-traffic faults with U0401/U0402 in the side object detection modules (also MKZ). Whether it is still current is not verified.

  • 2015–2017 · F-150

    Supported by vehicle data

    Ford SSM 46902: front controls (A/C, radio, window switches) faults with U0401 among other codes. Whether it is still current is not verified.

  • ASI-44656Status unverified

    BLIS/CTA faults with U0401 and/or U0402 in the side object detection modules

    2013–2014fusion · issued · NHTSA 10057738

    Service information for Fusion and MKZ with intermittent blind-spot or cross-traffic alert faults and these codes in the side object detection modules.

    We couldn't confirm whether this bulletin is still current, so it doesn't count as confirmation.

  • SSM 49157Status unverified

    MIL with U0100, U0401 and other codes

    2020escape · issued · NHTSA 10180361

    Service message for a 2020 Escape with the MIL on; the summary points to software.

    We couldn't confirm whether this bulletin is still current, so it doesn't count as confirmation.

  • SSM 46902Status unverified

    Intermittent A/C, radio or window switch control with U0140/U0401 and others

    2015–2017f-150 · issued · NHTSA 10127407

    Service message for F-150s with intermittent front controls and these codes in the front controls interface module.

    We couldn't confirm whether this bulletin is still current, so it doesn't count as confirmation.

  • U0402A module received invalid data from the transmission computer

    Same system Supported by vehicle data

    Ford's 2013-2014 Fusion and MKZ bulletin covers U0401 and U0402 together in the blind-spot modules: invalid data from the engine and from the transmission computer.

  • U0100Lost communication with the engine or powertrain computer

    Shares causes Supported by vehicle data

    Ford's 2020 Escape message lists U0100 and U0401 together and points to software.

  • U0140Lost communication with the body control module

    Shares causes Supported by vehicle data

    Ford's 2015-2017 F-150 message lists U0140 and U0401 together in the front controls interface module.

  • P061BEngine computer’s internal torque calculation check failed

    Shares causes Supported by vehicle data

    Mazda's bulletin 01-015-18 links U0401 with P061B and a lack of power when engine cranking is interrupted.

All Module network (CAN bus) communication codes

U0401 questions

What is the difference between U0100 and U0401?

U0100 means a module stopped hearing the engine computer. U0401 means it hears it but received data it rejects.

Should I fix other codes first?

Yes. U0401 often follows another fault the engine computer is reporting, so diagnose the engine and sensor codes first.

Sources and review

  1. Tech tip: Fusion U0401 DTC won't clear — ALLDATA ,
  2. Ford ASI-44656: BLIS/CTA faults with U0401 and/or U0402 in the side object detection modules — Ford Motor Company / NHTSA ,
  3. Mazda 01-015-18: Lack of power, check engine light, P061B:00 and U0401:00 — Mazda North American Operations / NHTSA ,
  4. 2023 Integra Owner's Manual: Indicator, Coming On/Blinking — American Honda Motor Co.
  5. Ford SSM 49157: 2020 Escape MIL with U0100, U0401, P166B, P1753, P0929, P0919 — Ford Motor Company / NHTSA ,
  6. Mazda SA-008-20: "Safety and Driver Support Systems Partially Disabled" with U0401:68 — Mazda North American Operations / NHTSA ,
  7. ASE L1 study guide: Network U-codes — Open Exam Prep
  8. Ford SSM 46902: 2015-2017 F-150 intermittent A/C, radio or window switch control with U0140/U0155/U0253/U0401/U0452 — Ford Motor Company / NHTSA ,
Last reviewed
Written by
Saurabh K.
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