U0401 Code: Invalid Data from ECM/PCM — Causes & Fix
U0401 means a module received invalid data from the engine control module (ECM/PCM) — the ECM is on the network but sending data that fails plausibility checks.
- Applies to
- All OBD-II vehicles (any make or model)
- Est. repair cost
- $50 – $800
- Time to fix
- 1–4 hours
What it means
Causes include an ECM fault, a sensor problem feeding the ECM, CAN wiring noise, or a software mismatch. U0401 is a generic OBD-II network/communication ("U") code defined in the SAE J2012 standard, so it applies to virtually any modern OBD-II vehicle regardless of make. These faults usually point to the vehicle's data bus (often CAN) or a module that has dropped off the network. Fix the wiring/module fault, then clear the code with a scan tool.
Symptoms
- Check engine light + other warnings
- Features or transmission behaving oddly
- Erratic operation
How to fix it
- 1
Scan the ECM for faults
1. Check the ECM for its own trouble codes and fix those first.
- 2
Check wiring/software
1. Inspect the CAN wiring for noise and confirm compatible module software. 2. Repair, then clear the code.
Frequently asked questions
Difference between U0100 and U0401?
U0100 means the ECM is not communicating at all; U0401 means it IS communicating but sending data that doesn't make sense. For U0401, fix the ECM's own faults first.
Last updated July 19, 2026
Guidance only — always consult a qualified professional or the official service manual before carrying out repairs.