What are the common causes of U0401?

The ECM/PCM A sending data the ECM rejects as invalid. A wiring or connector fault between the ECM/PCM A and the ECM. Low voltage that corrupts the ECM/PCM A messages. Software in the ECM/PCM A that is out of step with the ECM.

Read stored codes on every module and note codes paired with the ECM/PCM A code. Check the ECM/PCM A connector pins for corrosion or a poor fit. Test the wiring between the ECM/PCM A and the ECM. Check battery voltage and charging under load. Replace the ECM/PCM A if the data stays invalid. Clear the code and retest.

U0401

Invalid Data Received From ECM/PCM A

System: Network communication (U code)
Lamp: Check Engine Light
Category: Network Communications

What it means

U0401 means Invalid Data Received From ECM/PCM A.

Check these first

The ECM/PCM A sending data the ECM rejects as invalid
A wiring or connector fault between the ECM/PCM A and the ECM
Low voltage that corrupts the ECM/PCM A messages
Software in the ECM/PCM A that is out of step with the ECM

What to do next

Read stored codes on every module and note codes paired with the ECM/PCM A code
Check the ECM/PCM A connector pins for corrosion or a poor fit
Test the wiring between the ECM/PCM A and the ECM
Check battery voltage and charging under load
Replace the ECM/PCM A if the data stays invalid
Clear the code and retest

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Updated

Generic SAE J2012 definition. Last updated 2026-10-10.