B1861: Driver Knee Airbag Squib

Circuit fault

What B1861 means

Knee airbags deploy downward to keep the driver from sliding under the belt in a frontal crash. Like every other bag on the car, the knee unit fires through a squib, and the module watches that squib circuit for resistance inside a narrow window. When the reading goes open, B1861 is stored and the warning light comes on.

The loop for this bag runs from the module forward and down into the lower dash. It passes through a connector at the knee bolster and ends at the inflator winding. Because the bag lives in the footwell, its harness sees more feet, more dropped items, and more knee bumps than most of the SRS wiring on the vehicle.

Common causes

• The knee airbag connector unplugged and not reconnected after lower dash or steering column work
• Harness damage in the footwell from pedal work, kick panel removal, or aftermarket wiring
• An inflator squib that has failed open inside the knee airbag module
• Water at the driver floor from a leaking heater core or door seal reaching the connector
• A connector locking tab broken so the plug backs partway out
• Bent or corroded pins at the airbag control module under the console

Crash data or hardware fault?

The code tracks a live resistance reading, which is what defines the circuit family. It appears when the loop goes out of range and it drops out on its own once the circuit reads normal again. Crash data is the opposite case: a permanent memory entry written at deployment that a scan tool cannot reach and that our mail in reset is built to handle.

Does our reset clear it?

Clearing B1861 without fixing the open accomplishes nothing, since the module rechecks the loop within seconds of power up. Fix the connector, harness, or inflator first. If this vehicle also deployed and the module is holding crash data, mail the module in after the physical repairs and we will return it cleared so the system can arm.

Which makes throw it

Toyota and Lexus both carry B1861 for the driver knee airbag squib. Only models equipped with a driver knee bag will ever store it, which narrows the vehicles you will see it on.

What to do next

Drop the lower dash trim and find the knee airbag connector, since a plug left hanging after column or trim work is the single most common cause of this one. Confirm it is fully latched and the pins are clean. Next, measure the squib loop at the module end to decide whether the break is in the harness or the airbag. An inflator that reads open means the knee airbag assembly needs replacing, and we carry genuine OEM knee airbags. Related codes: B1826, B1866, 00589.