U0401: Invalid Data Received From ECM/PCM A — what it means, the affected system and what to check before replacing parts.
Meaning, symptoms, causes and checks
Invalid Data Received From ECM/PCM A. Basic catalogue definition; diagnostic details have not yet been reviewed.
Affected system: Network communication
Symptoms
- Illumination of the check engine light
- Vehicle entering limp mode due to power reduction
- Failure of the vehicle to start
- Loss of stability or traction control systems
Possible causes
- Defective sensors sending incorrect data to the PCM
- Weak battery or poor electrical supply voltage
- Damaged wiring or corroded electrical connectors
- Communication faults within the CAN bus network
- Internal failure of the PCM
What to check
- Test the battery and charging system for proper voltage and clean all terminal connections.
- Scan for additional diagnostic trouble codes to identify related component faults.
- Perform a wiggle test on the wiring harness while monitoring live data to isolate intermittent electrical faults.
- Verify proper signal integrity and continuity on the network data lines.
- Replace and reprogram the PCM only after confirming all other electrical and sensor components are functional.
Also written as: U0401-00, U040100, UO401 (some scan tools add the fault-type byte, e.g. -00).