B0004 DTC Code: Driver Knee Airbag Deployment Control Fault

The B0004 Diagnostic Trouble Code (DTC) indicates a fault in the driver's knee airbag deployment control circuit. This Body (B) code is related to the Supplemental Restraint System (SRS). When this code is stored, the airbag warning light typically turns on, indicating that the driver's knee airbag may not deploy properly during a collision.

What Does Code B0004 Mean?

B0004 means the SRS control module has detected an electrical fault in the driver's knee airbag deployment circuit. The problem may involve excessive resistance, low resistance, an open circuit, or a short circuit. Once detected, the module stores the code and may disable the affected airbag to prevent unintended deployment.

Symptoms of B0004

• Airbag warning light illuminated.
• SRS warning message displayed.
• Driver knee airbag disabled.
• Additional SRS trouble codes may be stored.

Common Causes

• Faulty driver knee airbag module.
• Damaged or broken wiring.
• Loose or corroded connectors.
• Short circuit or open circuit in the deployment circuit.
• Defective SRS control module.
• Previous accident damage or improper repairs.

How to Diagnose B0004

1. Scan the SRS system using a professional diagnostic scanner.
2. Inspect all wiring and connectors related to the driver's knee airbag.
3. Check for corrosion, loose terminals, or damaged harnesses.
4. Follow the manufacturer's diagnostic procedure before testing the circuit.
5. Repair the fault, clear the code, and verify it does not return.

Possible Repairs

• Repair damaged wiring.
• Replace faulty connectors.
• Replace the driver's knee airbag module if necessary.
• Replace or reprogram the SRS control module if required.
• Clear the DTC after completing repairs.

Can You Drive with B0004?

The vehicle will usually remain drivable, but it is not recommended to ignore this code. A disabled driver's knee airbag can reduce occupant protection in the event of a collision.

Estimated Repair Cost

Repair	Estimated Cost (USD)
Wiring repair	$50–$200
Connector replacement	$20–$80
Driver knee airbag replacement	$250–$900
SRS control module replacement	$300–$1,000

Frequently Asked Questions

Can I clear B0004 without repairing it?

No. If the electrical fault still exists, the code will return after being cleared.

Will B0004 cause an MOT or safety inspection failure?

Yes. In many countries, an illuminated airbag warning light will result in a failed safety inspection.

Is B0004 the same for every vehicle?

The general definition is similar across manufacturers, but the exact diagnostic steps and repair procedures vary depending on the make and model.

Conclusion

The B0004 DTC indicates a malfunction in the driver's knee airbag deployment circuit. Diagnosing and repairing the issue promptly helps restore proper SRS operation and ensures the airbag system can provide maximum protection during an accident.