B1650 is Toyota's code for a fault in the occupant classification system, the passenger seat sensing that decides whether the front passenger restraints should fire. Toyota writes it B1650/32. It usually shows up with the passenger airbag off lamp behaving strangely, and it lives under the seat rather than in the dash.
The occupant classification system reads what is in the front passenger seat. Its own control unit weighs and classifies the occupant, then reports to the center airbag sensor assembly. From that report the module decides whether the passenger airbag, the right front seat side airbag, and the right seat belt pretensioner should be armed. That is why a seat sensing fault touches three restraints at once.
Toyota sets B1650/32 when the module sees a fault in that circuit, whether that is a short, an open, a short to ground, or a short to battery held for a couple of seconds. Toyota's own service note tells the technician to stop troubleshooting the airbag side and go troubleshoot the occupant classification system as its own system, which is a fair sign of where the problem usually lives.
Trouble areas are the occupant classification system itself, the center airbag sensor assembly, the floor wire, and the number one seat wire. Three of those four are under or beside the passenger seat, in a spot that gets kicked, vacuumed, and slid back and forth for the life of the car.
Hardware, in the passenger seat. B1650 points outside the airbag control module in almost every case we see, at the seat unit and its wiring. The airbag sensor assembly is on the list because it is the part reading the signal, and it is the last suspect rather than the first.
Worth knowing before you buy anything: this system needs its calibration performed after the seat or sensor is disturbed. A mechanically correct repair with no calibration will leave the light on and the code back.
Depends what is behind it. A wiring or seat sensor fault has to be repaired, and no memory clearing touches that. Where a reset does come in is a vehicle that has been in a crash, because the airbag control module holds a locked deployment record separate from the seat sensing fault, and that record is what our airbag module reset clears.
Some occupant detection units also lock themselves after a deployment and hold their own stored data. Read us the part number off the unit and we will tell you whether it is something we service. Genuine OEM occupant classification sensors are searchable by vehicle if the unit itself is the failed part.
B1650/32 is Toyota and Lexus wording. Subaru uses B1650 in its own airbag chart for an occupant detection system malfunction, which is the same idea under a different manufacturer's numbering, so the diagnosis path differs even though the description reads alike. Confirm the make before working from either chart.
Clear the seat completely, then reseat the connectors under the passenger seat and look at the harness where it crosses the seat rails. Check for a repair splice, a chewed section, or carpet that has been wet. If everything under the seat checks out, the occupant detection unit is next, followed by the calibration step.
If the passenger airbag off lamp is stuck on with a normal sized adult in the seat, this is the code behind it most of the time. Related codes worth a look are B1610 for the front airbag sensor on the right, B1100 for the center airbag sensor assembly, and B1800 for the driver side firing circuit.
Related codes: B1610, B1100, B1800
Keep reading:
Code scope: Toyota, Lexus. The same number can mean something different on another manufacturer, so match the code to your make before you act on it.
A reset clears stored crash data. A replacement part fixes a hardware fault. We have read these codes since the nineties and will tell you which one you are looking at.
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Toyota parts and codes · Do not see it listed? Request a part or call 501-988-0611.