The B1878 OBD2 fault code relates to the Seatbelt Driver Pretensioner circuit. When the circuit short to battery, the module cannot properly monitor or control this body system.
At AIscanAuto, we help drivers quickly identify OBD2 trouble codes, understand their root causes, and find the right fix.
Symptoms
- Airbag / SRS warning light illuminated
- Seatbelt tensioner may not function
- Possible warning chime
- Safety system deactivated
Common Causes
- Faulty component — internal damage or wear affecting Seatbelt Driver Pretensioner
- Wiring issues — broken, corroded, or chafed wires in the circuit
- Connector problems — loose, oxidized, or moisture-damaged pins
- a short to battery voltage is detected — connects the signal line directly to 12V, causing constant high voltage
- Module input failure — rare, but the control module input stage may be defective
Step-by-Step Diagnosis
- Scan with OBD2 tool — Confirm B1878 is active. Check for additional DTCs.
- Visual inspection — Examine the Seatbelt Driver Pretensioner wiring and connector for corrosion or damage.
- Check voltage and ground — Use a multimeter to verify proper reference voltage.
- Test component — Compare readings to factory specs. A stuck or erratic signal confirms failure.
- Check for shorts/opens — Perform continuity tests on the wiring between the component and control module.
Repair & Solutions
- If the component is defective, replace the Seatbelt Driver Pretensioner with an OEM or quality aftermarket part.
- Repair any damaged wiring or connectors using proper methods.
- Clear the DTC with an OBD2 scanner and test drive to verify the code does not return.
- If the code persists after component replacement, inspect the control module connector.
Related Codes
- B1875 — Turn Signal / Hazard Switch Signal Circuit Failure
- B1876 — Seatbelt Driver Pretensioner Circuit Failure
- B1877 — Seatbelt Driver Pretensioner Circuit Open