B1057: Passenger Buckle Switch Circuit

Circuit fault

What B1057 means

S68/4 is the designation for the passenger buckle switch in the restraint system wiring. That switch closes when the belt tongue latches, and the control unit reads its state to decide how the passenger restraints should behave in an impact. B1057 says the unit cannot trust what it is seeing on that component or on the signal wire that carries it.

The code deliberately covers both ends of the problem. It might be the switch inside the buckle assembly, or it might be the wire between that switch and the control unit. Everything in between counts as well: the pigtail coming out of the buckle stalk, the connector under the passenger seat, and the pins where that harness terminates.

Common causes

• A broken conductor inside the buckle stalk pigtail where it flexes
• The connector under the passenger seat unplugged or partly latched after seat work
• Corroded pins in the under-seat connector from spilled drinks or a wet carpet
• A failed switch contact inside the passenger buckle assembly
• Signal wire chafed against the seat frame or crushed by the seat rail

Crash data or hardware fault?

B1057 is a live circuit reading rather than a record of a past event. The unit rechecks the buckle switch signal continuously and holds the code only while the reading is wrong. Stored crash data works by a different rule: written permanently after a deployment and impossible to erase with a scan tool, no matter how good the wiring is.

Does our reset clear it?

Reset service does not repair a switch or a signal wire, and B1057 returns on the next self test if the circuit is still bad. Repair the buckle, the pigtail, or the connector first. The mail-in service we run is for modules locked on crash data after a deployment, and it is the right step only once the physical repairs on the car are finished.

Which makes throw it

Both Honda and Mercedes-Benz carry B1057 in our lookup. The S68/4 designation comes out of Mercedes-Benz restraint system documentation, so expect that label in the wiring diagrams on those vehicles while the circuit itself does the same job on either make.

What to do next

Test the switch at the buckle first with the belt latched and unlatched, since that single check separates a dead switch from a wiring problem right away. Flex the stalk pigtail during the test to catch a conductor that is broken only under movement. If the switch behaves and the wire is open, trace the signal line back to the control unit connector and inspect the pins for corrosion or backed out terminals. Related codes: B00D5, B2-1X, B2765-11.