B0004 Driver Knee Bolster Deployment Control

The B0004 Driver Knee Bolster Deployment Control diagnostic trouble code indicates that the vehicle's Supplemental Restraint System (SRS) has detected a problem involving the driver knee bolster deployment-control circuit.

A driver knee bolster is a safety component located in the lower dashboard area beneath the steering wheel. During certain collisions, it can help control the movement of the driver's legs and knees.

On some vehicles, the knee bolster is a passive energy-absorbing structure. On others, the system may include a deployable knee airbag or electronically controlled restraint component. The exact design depends on the manufacturer.

When the SRS control module detects a fault involving the electronically monitored knee-bolster deployment system, it may store B0004 and illuminate the airbag or SRS warning light.

B0004 is therefore a safety-related body diagnostic code, not an engine or transmission fault.

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What Does B0004 Mean?

B0004 generally indicates that the restraint control module has detected an abnormal condition in the driver knee bolster deployment-control circuit.

Depending on the vehicle, the system may include:

• SRS control module

• Driver knee airbag or deployable knee bolster

• Deployment control circuit

• Inflator or actuator

• Wiring harness

• Electrical connectors

• Crash sensor information

The SRS module monitors the circuit for electrical abnormalities.

B0004 may be triggered by:

• Open circuit

• Short circuit

• High circuit resistance

• Low circuit resistance

• Faulty deployment component

• Damaged wiring

• Loose connector

• Corroded terminals

• Previous collision damage

• Incorrect component replacement

• SRS control module problems

The exact fault definition can vary by manufacturer.

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What Is a Driver Knee Bolster?

The driver knee bolster is located below the steering wheel, generally in the lower dashboard or instrument-panel area.

Its purpose is to help manage lower-body movement during a collision.

Depending on the vehicle, it can help:

• Support the driver's knees

• Reduce excessive leg movement

• Improve occupant positioning

• Help control lower-body motion

• Work together with seat belts and airbags

Some modern vehicles use a driver knee airbag, which can deploy from the lower dashboard area.

Others use structural knee bolsters designed to absorb crash energy without using an electrically controlled deployment system.

The presence of B0004 generally indicates that the vehicle has an electronically monitored or controlled restraint component related to the driver's knee area.

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Why Is B0004 Important?

B0004 is important because it concerns a passive safety and occupant-restraint system.

The knee bolster can work with other SRS components to help control driver movement during a collision.

Depending on the vehicle, the fault may affect:

• Driver knee airbag deployment

• Lower-body occupant protection

• SRS system monitoring

• Collision-response functions

• Overall restraint-system operation

The exact effect depends on the vehicle's safety-system design.

An illuminated SRS warning light should always be taken seriously.

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Symptoms of B0004

B0004 can produce several warning signs.

Airbag or SRS Warning Light

The most common symptom is an illuminated:

• Airbag warning light

• SRS warning light

• Restraint system warning light

SRS Warning Message

Some vehicles may display a message such as:

• Airbag system fault

• SRS malfunction

• Restraint system malfunction

• Safety restraint fault

Stored Diagnostic Trouble Code

On some vehicles, the only noticeable symptom may be:

• Stored B0004

• Illuminated SRS warning light

No Engine Performance Problems

B0004 normally does not cause:

• Engine hesitation

• Loss of engine power

• Poor fuel economy

• Transmission problems

The vehicle may drive normally while the restraint-system fault remains active.

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Common Causes of B0004

Several problems can trigger the B0004 code.

Faulty Driver Knee Airbag or Deployment Module

If the vehicle uses a deployable knee airbag or electrically controlled knee bolster, the component itself can develop an internal fault.

Possible problems include:

• Internal deployment-circuit failure

• Faulty inflator

• Incorrect circuit resistance

• Previous deployment

• Physical damage

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Damaged Wiring

The wiring between the SRS control module and the driver's knee restraint component may become damaged.

Possible problems include:

• Broken wires

• Chafed insulation

• Pinched wiring

• Open circuits

• Short circuits

• Excessive resistance

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Loose Electrical Connector

A connector may become loose after:

• Dashboard repairs

• Lower trim-panel removal

• Steering-column repairs

• Interior work

• Previous airbag replacement

A loose connection can cause an intermittent or permanent SRS fault.

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Corroded Connector Terminals

Moisture or contamination can cause:

• Corrosion

• High resistance

• Poor electrical contact

• Intermittent connections

The SRS module may then detect an abnormal deployment-circuit condition.

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Previous Collision Damage

If the vehicle has been involved in an accident, the driver's knee restraint system may have:

• Deployed

• Been damaged

• Been incorrectly replaced

• Sustained wiring damage

• Sustained connector damage

Incorrect collision repairs are a common cause of persistent SRS trouble codes.

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Incorrect Replacement Component

An incorrect knee airbag or restraint component may not match the vehicle's:

• Model

• Model year

• SRS configuration

• Airbag-system specification

The replacement component must be correct for the exact vehicle.

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Lower Dashboard Damage

The knee bolster is installed in the lower dashboard area.

Damage caused by:

• Collision impact

• Improper dashboard removal

• Incorrect installation

• Interior modifications

can affect the component or its wiring.

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SRS Control Module Fault

A problem inside the SRS control module is possible but should generally be considered only after checking:

• Knee restraint component

• Wiring

• Connectors

• Related SRS components

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Vehicles Commonly Affected by B0004

B0004 can occur on vehicles equipped with electronically monitored driver knee restraint systems.

Examples can include:

• Chevrolet Silverado

• Chevrolet Tahoe

• Chevrolet Suburban

• Chevrolet Camaro

• GMC Sierra

• GMC Yukon

• Cadillac Escalade

• Ford F-150

• Ford Explorer

• Ford Expedition

• Lincoln Navigator

• Toyota Camry

• Toyota Highlander

• Toyota Sequoia

• Nissan Pathfinder

• Nissan Armada

• Infiniti QX80

• Jeep Grand Cherokee

• Dodge Durango

• Volkswagen Atlas

• Audi Q7

• BMW X5

• BMW X7

• Mercedes-Benz GLE

• Mercedes-Benz GLS

• Volvo XC90

• Kia Telluride

• Hyundai Palisade

This is not a complete application list.

The exact meaning of B0004 can vary between manufacturers, model years, restraint modules, and vehicle safety-system designs. Manufacturer-specific service information should always be consulted before replacing an SRS component.

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How B0004 Is Diagnosed

B0004 should be diagnosed using a professional SRS/airbag-capable diagnostic scanner.

A basic OBD-II scanner designed primarily for engine codes may not provide enough information.

Scan the SRS Control Module

Retrieve:

• Current SRS codes

• Stored codes

• History codes

• Manufacturer-specific subcodes

• Deployment-circuit faults

• Related airbag codes

• Crash-sensor codes

• Seat belt and pretensioner codes

Additional codes can help identify whether B0004 is an isolated knee-restraint fault or part of a larger SRS problem.

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Inspect the Driver Knee Bolster Area

Technicians may inspect the lower dashboard for:

• Physical damage

• Previous deployment

• Incorrect installation

• Damaged trim panels

• Missing mounting hardware

• Evidence of previous repairs

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Inspect Wiring and Connectors

The associated wiring should be checked for:

• Broken wires

• Pinched wires

• Chafed insulation

• Loose connectors

• Bent terminals

• Corrosion

• Incorrect repairs

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Check the Deployment Circuit

Following the manufacturer's diagnostic procedure, a qualified technician may check for:

• Open circuits

• Short-to-ground conditions

• Short-to-power conditions

• Excessive resistance

• Faulty connectors

• Deployment-component faults

The exact diagnostic procedure and specifications vary by manufacturer.

Important: Knee airbags and related deployment circuits can contain pyrotechnic components. They should not be tested with improvised electrical equipment, test lights, or ordinary multimeters unless the manufacturer specifically permits the procedure.

Incorrect testing can create a serious safety risk or damage the SRS system.

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Check Related SRS Components

Technicians may also inspect:

• Driver airbag

• Seat belt pretensioner

• Crash sensors

• SRS control module

• Steering-column restraint components

• Other related deployment circuits

Related diagnostic codes can help identify the underlying problem.

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How to Fix B0004

The correct repair depends on the confirmed cause.

Repair Damaged Wiring

Possible repairs include:

• Replacing damaged wiring

• Repairing approved harness sections

• Restoring damaged insulation

• Correcting harness routing

• Securing the wiring properly

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Repair or Replace Damaged Connectors

Connector repairs may include:

• Terminal replacement

• Connector replacement

• Terminal-tension correction

• Approved corrosion repair

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Replace the Driver Knee Airbag or Deployment Component

If testing confirms an internal fault, the affected knee restraint component may require replacement.

The replacement part must match the vehicle's exact SRS configuration.

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Repair Previous Collision Damage

If the vehicle has been involved in an accident, proper repairs may be required for:

• Knee restraint components

• Wiring

• Connectors

• Airbags

• Crash sensors

• SRS control module

Simply clearing B0004 without correcting the cause is not a proper repair.

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Repair or Replace the SRS Control Module

If the restraint component, wiring, and connectors test correctly, the SRS control module may require further diagnosis.

Depending on the vehicle, this can involve:

• Software programming

• Module configuration

• Professional module repair

• Module replacement

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What to Do After Repairing B0004

After completing the repair:

1. Follow the manufacturer's SRS safety procedure.

2. Clear B0004 using an SRS-capable diagnostic tool.

3. Perform another complete SRS scan.

4. Check for additional deployment-system faults.

5. Confirm that the SRS warning light turns off.

6. Verify that the code does not return.

7. Confirm that the lower dashboard components are correctly installed.

The SRS system should not be considered repaired simply because the warning light temporarily goes out.

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Can You Drive With B0004?

The vehicle may continue to start and drive normally because B0004 does not usually affect:

• Engine operation

• Transmission operation

• Normal braking

• Steering operation

However, driving with an unresolved airbag or knee-restraint system fault is not recommended.

If the SRS warning light is illuminated, the vehicle's restraint system has detected a problem. The driver's knee restraint function should not be assumed to operate normally until the fault has been diagnosed and repaired.

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Is B0004 a Serious Code?

Yes. B0004 should be treated as a serious safety-related diagnostic trouble code.

Potential concerns include:

• Driver knee restraint may not deploy as designed

• Lower-body occupant protection may be affected

• SRS monitoring may be compromised

• Other restraint-system faults may be present

The vehicle can drive normally while the underlying safety fault remains.

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How to Prevent B0004

Recommended practices include:

• Do not modify SRS wiring.

• Do not connect aftermarket equipment to airbag circuits.

• Keep lower dashboard wiring properly secured.

• Use correct replacement restraint components.

• Have dashboard repairs performed carefully.

• Inspect the system after a collision.

• Keep electrical connectors dry.

• Never ignore an SRS warning light.

• Follow manufacturer procedures when removing lower dashboard panels.

• Have deployed restraint components replaced correctly.

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B0004 vs. Other Related SRS Codes

B0004 belongs to the body and restraint-system diagnostic code family.

Code	Description
B0004	Driver Knee Bolster Deployment Control
B0005	Collapsible Steering Column Deployment Control
B0010	Passenger Front Airbag Stage 1 Deployment Control
B0011	Passenger Front Airbag Stage 2 Deployment Control
B0012	Passenger Front Airbag Stage 3 Deployment Control
B0050	Driver Seat Belt Sensor Fault
B0052	Passenger Seat Belt Sensor Fault

The exact code definitions can vary between manufacturers.

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Final Thoughts

The B0004 Driver Knee Bolster Deployment Control diagnostic trouble code indicates that the vehicle's SRS or restraint control module has detected a problem involving the driver's knee restraint deployment-control system.

Common causes can include:

• Faulty driver knee airbag or deployment component

• Internal deployment-circuit failure

• Damaged wiring

• Open or shorted circuits

• Excessive circuit resistance

• Loose connectors

• Corroded terminals

• Previous collision damage

• Incorrect replacement components

• Lower dashboard damage

• SRS control module problems

The correct diagnostic process involves scanning the SRS module, checking related trouble codes, inspecting the lower dashboard and restraint components, and following the manufacturer's specified diagnostic procedure.

Because B0004 concerns a driver safety and restraint system, it should not be treated as a minor warning or simply cleared from the vehicle's memory. The underlying cause should be properly diagnosed and repaired.

Important safety note: Knee airbags and related SRS deployment circuits may contain pyrotechnic components. Always follow the vehicle manufacturer's safety and service procedures when working on the SRS system.