B0004 medium Severity

B0004: Driver Knee Bolster Deployment Control (Subfault)

Airbag warning light illuminated; potential reduced airbag system protection for driver’s knees in a collision

Overview

B0004 is an OBD‑II body code indicating a fault in the driver’s knee airbag deployment control circuit (subfault), typically involving wiring, sensor or module issues affecting the supplemental restraint system.

Common Symptoms

  • Airbag warning light illuminated on dashboard
  • Possible fault stored related to driver knee airbag circuit

Most Common Causes

Faulty driver knee airbag module medium

Component itself may be defective or damaged

Open or shorted driver knee airbag wiring harness high

Wiring issues commonly trigger subfault codes

Poor electrical connection in driver knee airbag circuit high

Connector corrosion or loose pins can cause fault

Restraints Control Module (RCM) fault medium

RCM may incorrectly detect cross‑coupled signals or be malfunctioning

Diagnostic Steps

  1. Connect a professional SRS‑capable scan tool and confirm B0004 presence
    Expected: Code B0004 stored in SRS / body module memory
    Interpretation: Verifies that system detects knee airbag deployment control subfault
  2. Visually inspect driver knee airbag wiring harness and connectors
    Expected: No broken wires, corrosion, loose or pushed‑out pins
    Interpretation: Damaged wiring likely cause if faults found
  3. Check continuity and resistance of driver knee airbag circuit
    Expected: Measured values within manufacturer spec
    Interpretation: High resistance/open/short requires repair of harness or connectors
  4. Test driver knee airbag module and RCM functionality with diagnostic tester
    Expected: Normal responses from module and RCM
    Interpretation: Module or RCM fault likely if responses abnormal

Repair Solutions

Repair or replace damaged wiring harness/connectors medium
Estimated Cost: $50 - $250

Labor and parts cost vary by vehicle and extent of damage

Replace driver knee airbag module hard
Estimated Cost: $300 - $800

Replacement requires SRS system reset and calibration

Repair or replace Restraints Control Module (RCM) hard
Estimated Cost: $500 - $1500

High cost and requires professional calibration

Common Misdiagnoses

Avoid these common diagnostic mistakes:

  • Incorrectly assuming powertrain or generic PCM code when code is body/SRS‑specific
  • Misreading a generic scanner as indicating speed sensor code (unrelated B0004 interpretation)

Frequently Asked Questions

What does the B0004 code mean?

The B0004 code stands for Driver Knee Bolster Deployment Control (Subfault). This generally indicates an issue with the Sensors system.

Reflecting on severity: How bad is B0004?

The B0004 code is considered medium severity. Airbag warning light illuminated; potential reduced airbag system protection for driver’s knees in a collision

How do I know if I have code B0004?

Common symptoms include: Airbag warning light illuminated on dashboard, Possible fault stored related to driver knee airbag circuit. You might also notice the Check Engine Light is on.

Potential causes for OBDII code B0004

This code is frequently triggered by: Faulty driver knee airbag module, Open or shorted driver knee airbag wiring harness, Poor electrical connection in driver knee airbag circuit.

What is the price difference for fixing B0004?

It depends on what needs to be fixed. Repair or replace damaged wiring harness/connectors repairs are cheaper (~$250), while Repair or replace Restraints Control Module (RCM) repairs are on the higher end (~$1500).

Is B0004 a generic or manufacturer-specific code?

B0004 is not specific to any one brand. It can appear on Ford, Dodge, Toyota, Honda, Jeep, and other vehicles.

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