U0298 High Generic / SAE

U0298: Lost Communication With DC/DC Converter Control Module A

Network and Communication Lost Communication (continued)

Do not keep driving

Get the vehicle somewhere useful now, and expect it to stop working with little warning.

Here is why, and it surprises most owners: your car has no alternator. The 12-volt battery that runs all its computers, lights and controls is kept charged by a converter that steps down power from the big traction battery. That converter has stopped, so nothing is charging your 12-volt battery — and when it goes flat, the car will not run, no matter how much charge the main battery shows.

That is the situation to avoid: an electric car showing a full battery that will not switch on. It is not the main battery, it is the little one.

You have however long that 12-volt battery lasts, which is not long with everything running. Drive straight to home or a workshop rather than continuing a journey, and switch off anything you do not need.

A jump start or a 12-volt charger will wake it up temporarily — enough to move it — but it does not fix anything and it will go flat again.

Do not investigate this yourself. The converter is on the high-voltage side, marked orange, and those voltages are lethal.

What this code means

The first DC to DC converter control module has stopped being heard from. See U0200 for the block's framing.

This is the most consequential code in the U02xx block for an electric or hybrid vehicle, and the reason is a fact many owners do not know about their own car: there is no alternator.

A conventional vehicle keeps its 12-volt battery charged with an alternator driven by the engine. An electric vehicle has no engine to drive one, and a hybrid cannot rely on an engine that spends much of its time switched off. So the job is done differently: a DC to DC converter steps the traction battery's high voltage down to around 14 volts and charges the 12-volt battery from it. It is the alternator's replacement, and it is the only thing keeping the 12-volt system alive.

Everything follows from that. The 12-volt battery does not drive the car — but it powers every control module, the contactors that connect the traction pack, the instrument cluster, the lights and the systems that let the vehicle be switched on at all. When it goes flat, the vehicle cannot function, and the state of charge in the traction pack is completely irrelevant.

That is the situation this page exists to explain, because it is genuinely counter-intuitive and it strands people: an electric car showing a full battery that will not switch on. The traction pack is fine. The 12-volt battery is flat, because the thing that charges it has stopped.

The practical advice is therefore urgent and specific. With the converter unavailable, the vehicle is running down its 12-volt battery from the moment the fault appears, and there is no way to recharge it while driving. The remaining time is however long that small battery lasts under the load of a running vehicle — which is not long. Get it somewhere useful immediately, and expect it to shut down without much warning. This is marked as not drivable for that reason.

Two things worth knowing. A conventional jump start or 12-volt charge will wake the vehicle temporarily, which can be enough to move it — but it does not fix anything, and the vehicle will flatten it again. And the high-voltage caution applies: the converter sits on the orange side, and it is not to be investigated at home.

Likely causes

Start here

Failed power or earth supply to the module · moderate
Corroded or loose connector · easy
Damaged data bus wiring · moderate
Faulty DC-DC converter · specialist

Less common

Blown fuse or failed supply · easy
Water ingress into module · 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.

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