B1787: Rear Left Occupant Collision Record

Stored crash data

What B1787 means

Rear seating positions on some Toyota and Lexus models carry their own occupant detection so the restraint system knows who is back there. The rear left sensor reports load and load change to the classification ECU, and the ECU passes that to the airbag control module. B1787 is written when the sensor reports force at a level the module treats as impact, and the entry stays put once written.

A stored record behaves differently from a wiring complaint. The module is not telling you a wire is open right now. It is telling you that an event was captured at some point in the past on that rear left position, and that event stays on the books until the correct procedure removes it or the module is reset after repairs.

Common causes

• A rear impact or side impact that loaded the rear left seat sensor
• Cargo dropped hard into the rear left seating position with the key on
• Rear seat removal, folding, or reinstallation that stressed the sensor mount
• A sensor calibration that was never performed after earlier seat or trim work
• An occupant classification sensor that failed and reported a false load event
• Water damage in the rear floor area reaching the sensor or its connector

Crash data or hardware fault?

B1787 is stored crash data. Live circuit codes rise and fall with an electrical reading and disappear on their own once the reading returns to normal. A stored record does not work that way. It was written to memory when the event happened, and a generic scan tool clear will not touch it, which is exactly the situation the mail in reset exists for.

Does our reset clear it?

Yes, the reset applies to this one once the vehicle side is handled. Repair or replace whatever deployed or was damaged, verify the rear seat sensors and their wiring, then mail the module to us and we return it cleared and ready to arm. Doing the reset before the repairs only hides the record and leaves the vehicle in a state nobody should drive.

Which makes throw it

Toyota and Lexus share B1787, and it appears on models equipped with rear occupant classification. Vehicles without rear seat sensing will not carry this code at all, so its presence tells you the chassis has that hardware.

What to do next

Look for physical evidence of an impact at the rear or left side before touching anything electrical, since a real event changes the whole plan. Inspect the rear seat belts for locked retractors and check whether any airbag or curtain deployed. If the seat was simply out of the car for repair work, follow the manufacturer calibration procedure and recheck. When deployment data is present in the module, send it in for a reset after the replacement parts are installed. Related codes: B1785, B1790, B220B-00.