CAN network

U0401 — Invalid Data Received from ECM/PCM

Severity: medium Drive with care, to a shop

What U0401 means

A control module on the vehicle network received messages from the engine control module (ECM/PCM) that failed its validity checks, being corrupted or out of range. Modules normally exchange such messages constantly over the CAN bus. The cause is most often wiring, power or ground trouble, less often a software glitch or a failing ECM.

Symptoms

  • Check engine light and other warning lights on
  • Intermittent power loss, hesitation or stalling
  • Delayed or erratic transmission shifts
  • Erratic gauge cluster readings
  • ABS or traction control disabled
  • Problem comes and goes
  • Some functions of the affected module unavailable

Possible causes

  1. Damaged CAN bus wiring or connectors (open, short, chafed harness)
  2. ECM/PCM power or ground problem
  3. ECM/PCM software glitch or outdated calibration
  4. Low system voltage corrupting messages
  5. Interference from aftermarket electronics
  6. A failing sensor feeding bad data to the ECM
  7. Failed ECM/PCM

How to diagnose

  1. Scan all modules and note which ones lost communication or report problems with the ECM
  2. Test battery voltage and charging system output
  3. Inspect CAN connectors and harnesses, especially near the ECM and at rub points
  4. Check ECM/PCM power and ground circuits against the wiring diagram
  5. Measure resistance between CAN-H and CAN-L at the diagnostic connector (about 60 ohms is normal) and check bus voltages
  6. Remove any aftermarket electronics such as alarms, stereos or add-on devices
  7. Check for ECM software updates from the manufacturer
  8. Unplug suspect modules one at a time, only following a documented procedure

Common fixes

  • Repair or replace damaged CAN wiring and connectors
  • Restore ECM power and ground connections and clean contacts
  • Reflash or update the ECM/PCM software
  • Replace a weak battery or faulty alternator if voltage is low
  • Replace the ECM/PCM with a VIN-matched unit as a last resort

U0401 on different brands

Ford · manuals
On the Ford Explorer, U0401:00 is set by the power steering control module (PSCM) when it receives invalid data from the ECM/PCM; this applies to the specific EPAS controller and model years.

Questions and answers

What does U0401 mean?

A module on the CAN network received corrupted or invalid data from the engine computer. It is a communication fault and doesn't always mean the ECM itself is bad.

Can I drive with U0401?

Only briefly and with care. Power loss, rough shifting and disabled safety systems are possible, so get it diagnosed soon.

Do I need to replace the ECM for U0401?

Usually not. Check CAN wiring, power and grounds, battery voltage and software updates first. ECM replacement is rarely the answer.

This is general information about the code. The meaning can differ between makes and models: a scan tool and the repair manual for your car will show the exact cause.