U3002 Low Generic / SAE

U3002: Vehicle Identification Number

Network and Communication Control Module Power and Ignition Supply

What to do

This is almost always about a part that has been replaced rather than a fault.

Every significant computer in your car stores its vehicle identification number, and they check each other. A module that has been replaced — or fitted second-hand from another car — carries the wrong VIN until somebody programs the right one in.

If your car has had any module replaced recently, go back to whoever did it. Writing the VIN is part of fitting the part, and it was missed. Nothing is broken.

If you have recently bought the car and nothing has been replaced that you know of, this is worth asking about — it means a module in the car came from a different vehicle. That may be perfectly innocent, but it is a fair question to put to the seller, and it can matter for warranty and immobiliser work later.

What this code means

A module is reporting a problem with the vehicle identification number.

This range is different from every other network family, and the difference decides how it should be diagnosed.

U01xx and U02xx say a module went silent. U04xx and U05xx say a module is talking nonsense about something it watches. This range says a module is reporting a problem with its own foundations — its supply, its earth, or the ignition state that tells it whether the car is even meant to be awake.

Which makes these codes upstream of almost everything else. A module with a marginal earth does not fail cleanly; it reports implausible values about every sensor it reads, sets codes in unrelated systems, and drops off the bus intermittently. A scan tool showing thirty codes across five systems very often has one of these underneath it.

So read this family first and fix it first. Clearing a page of downstream codes before the supply fault is repaired produces a page of downstream codes again by the end of the week.

And start with the battery, genuinely. Not as a formality — a twelve-volt battery weak enough to sag during cranking, or a terminal with corrosion under a clamp that looks tight, reproduces this entire family exactly. It is the cheapest thing to eliminate and by some distance the most common cause.

Every module of any consequence stores the VIN, and they check each other's copies — which is why this is a code rather than a piece of trivia.

The VIN is how a module knows it belongs to this car. It is written during manufacture and re-written when a module is replaced, and the network compares copies: a module whose VIN does not match the others is either a replacement that was never coded, or a part from a different vehicle.

So this code is overwhelmingly about work that has been done rather than a failure. A second-hand module fitted without coding, a replacement module left with a blank or default VIN, or a repair where one module was programmed and another was not.

It has a practical significance beyond diagnostics: manufacturers use VIN matching to decide whether a car is what it claims to be, and a mismatch can complicate warranty work, immobiliser matching and, for a buyer, the question of what has been replaced.

On a used car, this code is worth reading as history. It says a module in this vehicle came from somewhere else — which may be entirely innocent, and is worth knowing either way.

Likely causes

Start here

Low system voltage · easy
Corroded or loose connector · easy
Second hand module locked to another vehicle · specialist
Incorrect module configuration after replacement · specialist

Less common

Module not coded to the vehicle · specialist
Interrupted module programming · specialist
Damaged data bus wiring · moderate

Symptoms

Components involved

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.