U0551: Invalid Data Received From Impact Classification System Module
What to do
Treat this as the important one. It concerns the passenger airbag, and how the car decides whether — and how hard — to deploy it.
If the "passenger airbag off" light is on with an adult sitting there, that airbag is disabled. Carry front passengers in the back seat until this is repaired, and do not put a child in the front at all.
Two things you can check yourself, and both are common causes. Is anything stored under or wedged beside the passenger seat? The system weighs the seat, and objects loading it confuse it. And has the seat been removed, refitted, or had a cover put on it recently? Both usually require the system to be recalibrated.
Get this seen quickly. Everything else in this range can wait; a restraint that may not deploy correctly cannot.
What this code means
The impact classification system 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 is a restraints module, and it is the most safety-critical code in this batch by a wide margin.
Occupant classification decides how the passenger airbag behaves — whether it deploys at all, and at what force. It reads weight and position sensors in the passenger seat to distinguish an adult from a child from an empty seat from a child restraint, because an airbag that deploys at full force into a rear-facing child seat is lethal, and one that does not deploy for an adult is equally so.
So when this module publishes data the restraints controller cannot accept, the safe response is to disable the passenger airbag and light the warning. The 'passenger airbag off' lamp being on with an adult in the seat is the symptom to watch for.
The physical causes are unusually specific and unusually mundane. Anything under the seat that loads the sensing — a stored bag, a child's toy, an aftermarket bracket, a seat-mounted accessory — changes what the system weighs. Wiring under the seat is trapped by the seat rails, exactly as at U0509. And a seat that has been removed and refitted, or had a cover fitted, frequently needs the classification system recalibrated.
Do not seat a child in the front while this is stored, and treat a passenger airbag warning as a reason to move passengers to the back rather than a light to ignore.
Likely causes
Start here
Less common
- Corroded or loose connector · easy
- Faulty restraints control module · specialist
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
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