What It Means
B0004 is a Body (B) diagnostic trouble code that points to an open circuit in the driver’s frontal airbag Stage 2 deployment control. Many modern airbags have dual-stage inflators:
- Stage 1 is the primary deployment (for lower-severity crashes).
- Stage 2 provides additional force for higher-severity crashes.
An “open circuit” means the SRS (Supplemental Restraint System) control module is not detecting proper continuity in the Stage 2 circuit. This is usually caused by broken wiring, damaged connectors, or a failed airbag component.
Source: OBD-Codes.com – B0004
Symptoms
- Airbag/SRS warning light illuminated on the dashboard
- Airbag system partially or fully disabled
- In some cases, Stage 1 may still function, but Stage 2 will not, compromising full deployment in a severe crash
- No drivability issues, since this fault only impacts the restraint system
Severity / Priority Level
High. This is a critical safety issue. If left unresolved, the driver’s airbag may not provide the intended level of protection in a serious collision. Immediate repair is recommended.
Common Causes
- Open circuit in wiring between the SRS control module and the driver’s airbag Stage 2 inflator
- Damaged or defective clock spring in the steering column
- Loose, corroded, or damaged connectors in the airbag circuit
- Faulty driver airbag module (Stage 2 inflator side)
- Failed SRS control module
Sources:
Possible Fixes
- Scan the vehicle with a professional SRS-compatible diagnostic tool
- Inspect wiring harnesses and connectors for opens, damage, or corrosion
- Test continuity in the Stage 2 circuit between the control unit and airbag inflator
- Replace defective clock spring if open circuit is traced to steering column wiring
- Replace the driver’s airbag module if testing confirms Stage 2 inflator fault
- If wiring and components test good, consider replacement or reprogramming of the SRS control module
- Clear DTCs and verify the repair by retesting the system