U0554: Invalid Data Received From Accessory Protocol Interface Module
What to do
The car drives normally. Before anybody charges you for this one, do the free test.
Unplug everything — phone cables, chargers, USB sticks, dash cameras, any adapter in the accessory socket — and see whether the fault comes back over the next few days. This module is the car's translator for things you plug in, so the commonest cause is something plugged in. Cheap chargers are the usual culprits: they inject electrical noise the car was never designed to hear.
If the car's battery goes flat when it stands for a few days, mention that specifically. A device that keeps this interface awake stops the whole car going to sleep, and that is the version of this fault that costs money.
If it persists with nothing connected, then it is worth looking at properly — and any recent software update is worth mentioning.
What this code means
The accessory protocol interface module is broadcasting data that cannot be accepted as true. See U0400 for what an invalid-data code is and why the module it names is usually the messenger rather than the culprit.
This module is a translator, and knowing that changes where you look.
It sits between the vehicle's own network and whatever has been plugged into it — phone projection, USB and media devices, aftermarket accessories, and the connectors a manufacturer provides for dealer-fitted options. Its job is to keep the outside world from speaking directly to the car's bus.
Which makes it, by design, the module most exposed to things the manufacturer never tested. A cheap charger that injects electrical noise, a phone cable with poor screening, an accessory drawing more than the port expects, or a device that keeps talking after the car is locked — all of them reach the vehicle through here.
So the first diagnostic step costs nothing: unplug everything. Remove every accessory, cable, charger and adapter, clear the code, and see whether it comes back. A fault that disappears when the car is empty has been diagnosed, and no part needs replacing.
The second is the sleep question. A device that holds this interface awake stops the vehicle shutting down, and the owner meets that as a flat battery after a few days rather than as a fault.
Likely causes
Start here
- Aftermarket head unit fitted in place of the original · moderate
- Module not coded to the vehicle · specialist
- Corroded or loose connector · easy
- Poor wiring splice in an aftermarket installation · moderate
Less common
- Software updated on one module only · 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.
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