U0400 Moderate Generic / SAE

U0400: Invalid Data Received

Network and Communication Invalid Data Received Emissions related

What to do

This code says a computer in your car is receiving information it knows cannot be true — not that anything has gone silent. That distinction matters for what happens next.

The most useful thing to understand: the fault is usually not in the module this code names. Modules pass on what their sensors tell them, so a module broadcasting an impossible figure is often faithfully repeating a lie it was told by a failing sensor somewhere else. Replacing the module named by this code is a common and expensive mistake.

Ask for all the other stored codes to be read and dealt with first. On this kind of fault, any code that names a specific sensor or component is far more informative, and fixing that usually makes this one disappear.

Two things worth mentioning if they apply. If this appeared straight after a module was replaced, software was updated, or something was retrofitted, it may be a configuration mismatch rather than a fault — two computers that do not agree about what they are talking to. And if the car is genuinely misbehaving in some way, the data may be entirely accurate and simply reporting something real.

What this code means

A module is receiving data it cannot accept as true.

This is the first code of a family that is fundamentally different from the lost-communication codes at U01xx and U02xx, and understanding the difference is worth more than anything else on this page.

A lost communication code means a module went silent. Something stopped arriving, and the reasons are the ones set out at U0100: power, earth, bus wiring, another module jamming the network.

An invalid data code means the opposite — the module is talking, and what it is saying cannot be true. The messages are arriving, on time, correctly formed. Their content is impossible: a road speed that disagrees with every wheel, a temperature outside anything physics allows, a torque figure that does not match the engine's own report, a value that never changes when it must.

Four consequences follow, and they invert several of the usual habits.

First, everything a lost-communication fault would have you check is already proven good. The named module has power, it has an earth, and its bus connection works — otherwise it could not be talking at all. So starting with supply and wiring, which is right for U01xx, is largely wasted effort here.

Second, and most importantly: the fault is usually not in the module the code names. A module reports what its own sensors tell it. If the anti-lock braking module is broadcasting an impossible wheel speed, the likely fault is a wheel speed sensor — the braking module is faithfully passing on a lie it was told. The code names the messenger, and the messenger is usually honest. That single reframing is what stops the wrong part being replaced.

Third, the receiving module may be the one at fault — by not understanding. Where two modules run software or calibrations that do not belong together, one sends correctly and the other rejects what it gets. A code like this appearing immediately after a module replacement, a software update or a retrofit is a configuration mismatch rather than a failure, and it belongs with the software incompatibility family at U03xx.

Fourth — and this is the one people dismiss — the data may be perfectly accurate. A module reporting a value the receiver refuses to accept may be correctly reporting something genuinely, physically wrong. Before deciding the network is lying, it is worth asking whether it is telling the truth about a real fault, and whether any other stored code describes that fault directly.

So the order of work here is: read every other stored code first. On this family, the codes that name a specific component are far more informative than this one, and this one is very often a downstream consequence of them.

Likely causes

Start here

Faulty receiving module input · specialist
Damaged data bus wiring · moderate
Corroded or loose connector · easy
Software updated on one module only · specialist
Incorrect module configuration after replacement · specialist

Less common

Another module holding the bus down · specialist

Symptoms

Components involved

Commonly seen with

Information, not instruction

CarGeek is a reference, not a service manual. Its pages are written from public sources and from what other people have found, never from a manufacturer's own service information, so they can be wrong or incomplete for your particular vehicle. Some of what they describe carries real risk: high voltage, fuel under pressure, stored energy, hot and moving parts.

Have anything you intend to act on checked by a trained person against the manufacturer's own procedure for your vehicle. Nothing here replaces that procedure.

Community experience

Be the first to write this up

Nothing posted about this yet. Whatever you found is worth writing down — even a dead end saves someone the same afternoon.

What makes one worth reading:

The car — make, model, year and engine. The same fault behaves differently on each.
What you measured, not only what you replaced.
What actually fixed it — or that nothing did, which is worth knowing too.