B1879: Driver Belt Pretensioner, Shorted

Circuit fault

What B1879 means

Ford breaks pretensioner circuit diagnosis into several codes so the restraint control module can say what kind of fault it found rather than just reporting a bad reading. B1879 is the shorted condition on the driver belt pretensioner, meaning resistance has collapsed well below what a healthy firing loop measures.

Knowing which of the split codes is set saves time. A shorted reading sends you looking for two conductors in contact or an inflator that has shorted internally, rather than hunting for a break or a corroded terminal the way a high or open code would.

Common causes

• The pretensioner wire pair chafed together behind the B pillar trim
• Harness crushed under the sill plate or the seat track
• Moisture in the retractor connector bridging the terminals
• A pretensioner that has shorted internally in the retractor
• Damage from carpet, trim, or seat work that pinched the pair

Crash data or hardware fault?

B1879 is a circuit fault that reflects a measurement the restraint control module takes live, so it clears once the short is gone. Crash data is the separate category, written permanently when the restraints deploy and impossible to erase with a scan tool, which is why those modules come to us instead.

Does our reset clear it?

A reset does not correct a shorted pretensioner circuit. The module measures the loop again at the next key on and stores B1879 right back. Repair the wiring or replace the retractor first. Our mail-in reset applies to Ford restraint modules that hold crash data after a deployment, once the belts and airbags have been replaced.

Which makes throw it

B1879 is a Ford code in our lookup, covering the driver seat belt pretensioner circuit on vehicles using the restraint control module.

What to do next

Note every pretensioner code the module has stored, because Ford's split means the companion codes tell you which failure mode the module actually saw. Pull the driver B pillar trim and measure between the two pretensioner wires with the retractor unplugged to place the short. If the retractor reads shorted on its own, the belt assembly is the part, and we stock genuine OEM Ford seat belts. Related codes: B1878, B1881, B1134, B1318, B1933.