U0401🔧 Vehicle network (CAN bus) and engine computerStop and fix promptly

U0401: Invalid Data Received From ECM/PCM A (Meaning, Causes, Fixes)

Reviewed 2026-10-23 · Based on 3 cited source(s)

What U0401 means

Modern vehicles have many control modules that share information over a data network called the Controller Area Network (CAN) bus. The engine control module (ECM), or powertrain control module (PCM), manages the engine using inputs from sensors throughout the vehicle and broadcasts that information to other modules (RepairPal, KBB). Each module expects a specific type of information from the modules it listens to (CarParts.com). RepairPal says U0401 indicates one or more modules on the vehicle have received invalid data from the ECM, and CarParts.com says it is logged when modules on the data network receive implausible data from the ECM/PCM. So the module that stored U0401 is usually not the one at fault; the problem is in the data coming from the engine computer or in what feeds it. The "A" simply labels the first ECM/PCM in the manufacturer's network design. Note on sources: KBB words it differently, saying the code indicates a communication failure between two or more modules and that the PCM checks the information being passed and sets the code when it detects invalid data. RepairPal and CarParts.com describe other modules receiving bad data from the ECM/PCM. CarParts.com also notes the exact definition can vary by manufacturer, so check your vehicle's service information. U0400 is the general Invalid Data Received code (RepairPal), and U0100 is the separate code for lost communication with the ECM/PCM.

Severity: can I keep driving?

Stop and fix promptly

Get it diagnosed soon. KBB calls U0401 not always serious but urgent, because depending on the cause it can bring a loss of power, a no-start, limp mode, or disabled traction and stability control. RepairPal rates it Moderate, meaning it may not threaten safety right away but should be checked within a reasonable time. If the car loses power, goes into limp mode, or the traction or stability control lights come on, drive gently and get it checked right away.

Common symptoms

Likely causes

Roughly most to least common, based on the sources below. Your vehicle may differ.

  1. A dead battery, charging system problems or abnormal system voltage (RepairPal, KBB, CarParts.com)
  2. Disconnected, damaged, burnt, shorted or corroded wiring or connectors in the ECM/PCM harness (KBB, CarParts.com)
  3. Faulty sensors, especially engine and drivability sensors, causing the PCM to send invalid data; KBB says these usually set their own codes too (KBB, CarParts.com)
  4. A problem with the CAN bus data network (RepairPal, CarParts.com)
  5. ECM/PCM problems; KBB says a faulty control module is a rare cause (RepairPal, KBB, CarParts.com)

Diagnostic steps you can do

⚠ Before you start

Work on a cool engine, parked on level ground with the parking brake set. Never work under a car supported only by a jack.

  1. Read and write down all stored codes and freeze frame data in the order they were stored, then clear the code and see if it returns; RepairPal says U0401 can pop up intermittently or after a dead battery, especially as a history code (RepairPal, KBB).
  2. Check the battery and charging system first and repair them as needed, since the ECM needs proper voltage to work (RepairPal).
  3. Fix any other codes first, especially sensor and engine codes; RepairPal says additional codes should be addressed before diagnosing U0401, and several communication codes together point to the CAN network (RepairPal, KBB).
  4. Look over the wiring and connectors at the ECM/PCM for broken, loose, burnt or corroded wires (RepairPal, KBB).
  5. Check for technical service bulletins (TSBs) for your vehicle, since a known fix can save a lot of diagnostic time (RepairPal, KBB).

Typical fixes

Repair costs vary widely by vehicle, region, parts brand and shop, so we don't quote prices. Get a written estimate after diagnosis.

🛠 When to call a pro

  • KBB says this code often needs diagnostic tools and equipment specific to your make and model, and a generic scan tool may not give you the information you need
  • Testing the wiring for ground integrity, continuity and resistance and testing the communication circuit and CAN bus between modules needs a multimeter, wiring diagrams and network know-how (KBB)
  • The code returns after the battery, charging system and visible wiring check out and other codes are fixed
  • The car won't start, loses power, or runs in limp mode

Where to buy

Plain search links. Always match parts to your exact year, make, model and engine.

OBD2 scanners on Amazon Parts at Advance Auto Parts catalog at RockAuto

FAQs

Is U0401 serious?

It depends on the cause. KBB says it is not always serious but is urgent, since it can cause a loss of power, a no-start or disabled traction and stability control. RepairPal rates it Moderate. Get it diagnosed soon.

Can I keep driving with U0401?

KBB says it can affect drivability, especially if traction and stability control are affected, and recommends diagnosing it as soon as possible. If the car loses power or goes into limp mode, drive gently and get it checked right away.

What's the difference between U0401 and U0100?

U0401 means modules are receiving invalid data from the ECM/PCM, per RepairPal and CarParts.com, so messages are still arriving but don't make sense. U0100 means communication with the ECM/PCM has been lost.

How much does it cost to fix U0401?

None of the sources give a repair cost. It can range from charging or replacing a battery or fixing a corroded connector to repairing network wiring or replacing a control module, so get a diagnosis and a written estimate first.

Sources

  1. RepairPal: U0401 Invalid Data Received From ECM/PCM "A" (rated Moderate)
  2. KBB: U0401 Code, Invalid Data Received From ECM/PCM A (KBB Service Advisor, reviewed by Gary Hardesty)
  3. CarParts.com: U0401 Code, Invalid Data Received from ECM/PCM "A" (reviewed by William Guzenski, ASE Master Technician)

Last reviewed 2026-10-23. Code definitions and repair steps can vary by manufacturer. Confirm with your vehicle's service information.