B1B79: Seat Weight Sensor 3, Low

Circuit fault

What B1B79 means

The passenger seat sits on a set of weight sensors, one at each mounting corner, and the occupant classification module adds their readings together to estimate who or what is in the seat. Sensor 3 is the left front unit. When its input line reads below the expected range, the module stores B1B79 and stops classifying with confidence.

That classification decides whether the passenger airbag arms, and on many vehicles it drives the passenger airbag on and off indicator. A single corner reading low skews the total, so the module would rather flag the fault than make an arming decision from a number it knows is wrong.

Common causes

• The left front sensor connector unseated or corroded under the seat cushion
• A pinched wire where the seat harness crosses the track at the front of the seat
• A failed sensor at that mounting point after years of load cycles
• Seat bolts torqued incorrectly or shimmed after a seat removal, loading the sensor wrong
• Liquid spilled through the seat cushion reaching the sensor or its terminal

Crash data or hardware fault?

This belongs in the circuit group because the module is reporting a live electrical reading on the sensor input. Reconnect the wire and the value changes. Crash data is stored history instead. It records a deployment that has already happened, lives permanently in module memory, and no scan tool erases it.

Does our reset clear it?

Clearing the module does not raise a low sensor input. The occupant classification module reads that same line at the next key on and sets B1B79 again. Repair the connector, wiring, or sensor first, and expect the system to need its calibration procedure afterward. Our mail-in reset is for airbag modules holding crash data or a stored internal fault.

Which makes throw it

B1B79 shows on Chrysler vehicles in our lookup, on seats equipped with the four corner weight sensing setup.

What to do next

Move the seat rearward, then check the sensor connector at the left front mounting point while watching for a wire caught under the track. A harness rubbed through at that spot is common on seats that get adjusted often. If the connector and wiring are good, measure the sensor input at the module to decide whether the sensor itself has failed, and plan on running the occupant classification calibration after any repair. Related codes: B1B56, B1B7E, B1035.