U0297: Lost Communication With AC/DC Converter Control Module B
What to do
The car will still charge, but roughly half as fast — because it has two chargers and one has dropped out.
The useful thing to know is that this is not your battery wearing out, which is what it looks like. A tired battery holds less charge; this makes the car take longer to reach the same charge. If it still gets to 100% but takes about twice as long as it used to, that is this fault, not degradation — and unlike degradation, it is fixable. Worth saying clearly, because the two get confused constantly.
Another clue: rapid DC charging will be unaffected. Rapid chargers bypass the part that has failed, so if the car still rapid-charges at full speed but home charging has halved, that confirms it.
Meanwhile plan for longer charging times rather than being caught out.
Ask for the 12-volt battery to be tested first — a weak one causes charging faults on electric cars and is cheap and commonly missed. And do not investigate the charging system yourself; the voltages involved can kill.
What this code means
The second AC to DC converter control module has stopped being heard from. See U0296 for what an on-board charger does and why losing it stops the vehicle being refuelled.
A second on-board charger exists to charge faster from AC. A single unit is limited by what it can convert and dissipate, so vehicles offering higher AC charging rates — the ones that can use a three-phase supply or a high-power home installation — do it by fitting two converters and splitting the load.
The consequence is more forgiving than at U0296 and worth predicting: charging usually still works, at roughly half the rate.
That produces a complaint that sounds like a battery problem and is not. An overnight charge that used to finish by morning now does not. A top-up on a journey takes twice as long. The natural conclusion is that the battery has degraded — and the actual cause is that half the charging hardware is unavailable.
The distinguishing evidence is available to any owner: charging rate, not charging capacity. A degraded battery holds less energy but still accepts it at the normal rate. A missing charger accepts the same energy at half the speed. If the car still reaches full charge but takes far longer to get there, that is this rather than a worn battery — and worth saying, because battery degradation is not a repairable thing and this is.
Rapid DC charging is unaffected, for the reason given at U0296: it bypasses the on-board chargers entirely. So a vehicle whose home charging has halved will still rapid-charge at full speed, which is another piece of evidence pointing here.
The ordinary causes apply, and the 12-volt battery deserves its check first as at U0293 and U0296.
Likely causes
Start here
- Failed power or earth supply to the module · moderate
- Corroded or loose connector · easy
- Damaged data bus wiring · moderate
- Blown fuse or failed supply · easy
Less common
- Water ingress into module · moderate
Symptoms
Components involved
Information, not instruction
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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
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