U0401 Invalid Data Received From ECM/PCM "A"

U0401 means the engine control module is talking, but the data it is sending fails a plausibility check. Communication is intact — the content is wrong, out of range, or inconsistent with what other modules report.

Code details

Generic OBD-II · U0

System: Computer
Code type: Generic (SAE / ISO controlled)
Standard: SAE J2012 / ISO 15031-6

Diagnostic boundary

A diagnostic trouble code reports that a monitored test failed. It does not prove one specific part is bad, and manufacturer logic can add vehicle-specific conditions.

Do not chase the network wiring for this one. The bus is working — that is what separates an invalid-data code from a lost-communication code — so the fault lies in what the engine control module is measuring or computing.

Symptoms of U0401

Check-engine light, sometimes with several unrelated codes at once.
Warning lights, a no-start, or intermittent electrical faults.
Communication or module-reset problems on a scan tool.

Common causes of U0401

Low battery voltage, poor grounds, corroded connectors, or blown fuses.
Wiring or network (CAN bus) faults between modules.
A module software/programming issue, or rarely a failed controller.

Useful checks before replacing parts

Read the stored codes inside the engine control module itself, because the reason its data is implausible is usually a fault it has already recorded against one of its own sensors.
Compare the suspect value against the same quantity as other modules see it, since a plausibility failure is a disagreement between sources rather than a missing signal.
Check the sensors feeding the sending module along with their wiring and grounds, because a skewed or intermittent input produces valid messages carrying invalid numbers.

Related OBD-II codes

These nearby computer entries can help compare wording and pin down the fault area.