What U0401 means
Another module in the car, such as the transmission or ABS module, is receiving messages from the engine computer, but the data doesn't make sense, so it ignores it. Often the engine computer is passing on a problem of its own, like a faulty sensor reading, or its software is outdated or doesn't match the other modules.
How the engine computer detects it
The ECM/PCM is present on the data bus but the values it reports are implausible — out of range, frozen, or failing the checksum or rolling-count check. The receiving modules reject the data. Implausible engine data can force limp mode or stall the engine. Causes include a faulty sensor feeding the module, internal computation errors, a software or calibration mismatch after a repair, or bus interference corrupting the frames.
Written from public technical sources and not yet checked by a mechanic. How we write these pages
Symptoms
- Multiple warning lights may illuminate
- Affected modules may go into limp mode or shut down
- Specific functions inoperative depending on module
- Diagnostic tools may show communication faults
Common causes
- ECM software bug or outdated calibration Possible
- ECM internal sensor or processing fault Possible
- CAN corruption causing checksum errors Possible
How to diagnose U0401
- Use a scanner that reads all modules to see which module stored U0401 and whether the engine computer has its own codes. Fix those engine codes first.
- Have the battery and charging system tested. Low or unsteady voltage can corrupt network messages.
- With the ignition off, check the engine computer's connectors and ground connections for corrosion or loose pins.
- Ask a dealer or shop about software updates for the engine computer and for the module that set the code.
- If the code started after a repair, such as a replaced or used engine computer, make sure it was programmed correctly for your car.
Vehicles that report U0401 most
| Vehicle | Years | Reports | Share | Median miles |
|---|---|---|---|---|
| Ford F-150 | 2012–2017 | 9 | — | |
| Honda Accord | 2018–2020 | 4 | — | |
| Honda Pilot | 2016–2019 | 4 | — | |
| Jeep Compass | 2014–2015 | 3 | 89k | |
| Dodge Dart | 2015–2016 | 3 | — | |
| Honda CR-V | 2017–2019 | 3 | — |
Counts of owner complaints to the NHTSA that mention U0401 (70 in total), not failure rates: popular models get more complaints simply because more of them are on the road. Models with fewer than 3 complaints are left out.
Reading the code
- U
- Network
- 0
- Generic (SAE) code
- 401
- Specific fault
Questions drivers ask
Can I drive with code U0401?
Usually yes, carefully, if the car drives normally. If the engine runs poorly, the transmission shifts oddly or several warning lights come on, keep the trip short. If it stalls or won't accelerate, have it towed.
Will my car pass an emissions inspection with U0401?
Probably not in states that test vehicles with an OBD-II scan: an emissions-related code that keeps the check engine light on is usually an automatic fail. Rules differ by state and county, so check yours.
Often reported together
Codes that owners mention in the same NHTSA complaints as U0401. They can point to a shared cause, so it's worth checking them together.
- U0416Invalid Data Received from Vehicle Dynamics Control Module7 complaints
- U0100Lost Communication with ECM/PCM "A"6 complaints
- P0722Output Shaft Speed Sensor Circuit No Signal4 complaints
- U0418Invalid Data Received from Brake System Control Module4 complaints
- U3003Battery Voltage4 complaints
- P0172System Too Rich Bank 13 complaints
This page is general information, not a substitute for a professional diagnosis. Repair costs are rough estimates for parts and labor and vary by vehicle and region.