B1C38: Driver Retractor Pretensioner, Low

Circuit fault

What B1C38 means

A retractor pretensioner fires a small charge that spins the belt spool and removes slack, holding the driver in position for the airbag. The restraint controller monitors its firing loop with a test current and compares the reading to a stored range. A value under that range causes B1C38 to be stored and the system to shut down.

The loop runs from the controller along the floor and up the B pillar to the retractor. Everything in that path affects the reading, including the connector at the retractor, the harness behind the sill and pillar trim, and the pretensioner itself. Vehicles that have had carpet replaced or an amplifier mounted under a seat are worth asking about, since that work runs through this harness.

Common causes

• Harness chafed or crushed behind the driver B pillar trim
• A retractor connector damaged or only partly seated
• Wiring pinched under the sill plate during carpet or trim work
• A pretensioner that has shorted internally
• Water running down the pillar into the connector

Crash data or hardware fault?

B1C38 is a live circuit reading and clears when the loop measures correctly again. Crash data is the opposite kind of entry, written into module memory at the moment the restraints fire and permanent from then on, which is why no scan tool can remove it from a deployed module.

Does our reset clear it?

A module reset does not fix a low pretensioner circuit, because the controller measures that loop again seconds after the key comes on. Repair the harness or replace the retractor first. Where the reset matters is a module holding deployment data after a crash, which we clear once the deployed belts and airbags have been replaced.

Which makes throw it

Dodge and Jeep both list B1C38, on the first row driver retractor pretensioner circuit.

What to do next

Remove the driver B pillar trim and inspect the retractor connector and the wiring behind it, since trim clips and the belt height adjuster are hard on that harness. Measure the loop at the retractor and again at the controller to place the fault. A shorted pretensioner means the seat belt assembly gets replaced, and we stock genuine OEM belts for these vehicles. Related codes: B1C29, B1C39, 0X93090D.