B0057: Third Row Centre Seat Belt Sensor
What to do
The belt still works as a belt — what is affected is the car knowing whether it is fastened. The chime may be wrong, and more importantly the airbag deployment plan for that seat is now based on a guess. Wiring under the seat is the usual cause and a straightforward repair, but it is part of the restraint system, so leave it to a workshop.
What this code means
The third row centre seat belt buckle sensor circuit is faulty.
This is the buckle switch — it detects whether the belt is fastened — and it is an input to the restraint system rather than one of its explosive devices.
Most people know it as the thing that makes the chime stop, and that is its least important job. The restraints module uses belt state to decide how to deploy, because a belted and an unbelted occupant need opposite treatment: an unbelted person is already moving toward the dashboard when the airbag fires, so the bag must inflate earlier and harder — while that same deployment into someone the belt is already holding back can do more harm than the crash.
So a buckle sensor that reports wrongly does not merely silence a chime. It makes the airbag deploy to the wrong plan. Reported unfastened when it is fastened gives an unnecessarily aggressive deployment; the reverse gives one far too gentle for someone who is unrestrained.
It is also what the pretensioner decision hangs on, since firing a pretensioner on an unused belt achieves nothing and spends a one-use device.
The commonest cause is not the switch. It is the wiring beneath the seat, which flexes every time the seat is adjusted and is routinely damaged by objects pushed underneath or by seats being removed and refitted. Check the harness and its connector before the buckle.
Likely causes
Start here
- Damaged wiring under the front seats · specialist
- Corroded or loose connector · specialist
- Faulty seat belt buckle switch · specialist
Less common
- Damaged wiring harness · specialist
- 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
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.
Sign in or create an account to add what you found about B0057.