What is an OBD2 code?

An OBD2 (On-Board Diagnostics) code is a diagnostic trouble code (DTC) generated by your vehicle's computer system when it detects a problem. These codes help identify specific issues with your vehicle's engine, transmission, emissions, or other systems.

How do I read OBD2 codes?

To read OBD2 codes, you'll need an OBD2 scanner. Plug it into your vehicle's OBD2 port (usually located under the dashboard), turn your key to the 'ON' position, and follow your scanner's instructions to retrieve the codes. Each code starts with a letter (P, B, C, or U) followed by four numbers.

What do the different types of OBD2 codes mean?

OBD2 codes are categorized by their first letter: P (Powertrain) for engine and transmission issues, B (Body) for interior systems like airbags, C (Chassis) for mechanical systems like brakes, and U (Network) for computer and module communication problems.

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Home » OBD2 Codes » B0004

Code B0004

Symptoms

• Airbag warning light on the dashboard

• Airbag system not functioning properly

• Possible error messages on diagnostic tools

Common Causes

• Faulty knee airbag module

• Damaged wiring or connectors

• Malfunctioning airbag control unit

Glossary

Airbag: A safety device in vehicles that inflates rapidly in the event of a collision.

OBD-II: On-Board Diagnostics, a standardized system for vehicle diagnostics.

Related Codes

• B0001

• B0002

Laymans terms

This code means there's a problem with the part of the car that helps protect the driver's knees in a crash.

Explanation

The B0004 code indicates an issue with the system that controls the deployment of the knee airbag for the driver.

Technical description

The Driver Knee Bolster Deployment Control is responsible for managing the deployment of the knee airbag in the event of a collision. This code is triggered when the system detects a fault in the deployment circuit, which could be due to electrical issues, sensor malfunctions, or wiring problems.

Diagnosis steps

• Check the airbag warning light on the dashboard.

• Use a diagnostic tool to read the error codes.

• Inspect the wiring and connectors for damage.

Repair procedures

• Replace the faulty knee airbag module.

• Repair or replace damaged wiring or connectors.

• Reset the airbag control unit and clear error codes.

Tools required

• OBD-II scanner

• Multimeter

• Basic hand tools

Estimated repair cost

$200 - $600

Difficulty level

Moderate

Commonly affected vehicles

• Vehicle 1

• Vehicle 2

• Vehicle 3

Preventive measures

• Regularly inspect airbag system components.

• Ensure all recalls and service bulletins are addressed.

• Avoid tampering with airbag wiring.

Error code type

Safety System Issue

User experience recommendations

• Do not ignore the airbag warning light.

• Have the airbag system checked by a professional.

• Avoid driving the vehicle until the issue is resolved.

Warranty information

Airbag systems are often covered under vehicle warranties. Check with your manufacturer.

Historical data

This code has been associated with issues in vehicles where the knee airbag system was introduced as a safety feature.

Urgency level

High – This issue affects the safety system of the vehicle and should be addressed immediately.

Legal and safety notice

Driving with a malfunctioning airbag system can be dangerous and may violate safety regulations.

Testing conditions

• Vehicle stationary

• Ignition on

Component location

The knee airbag module is located under the dashboard on the driver's side.

FAQs

Q: Can I drive with the B0004 code?
A: It's not recommended to drive with this code active as it affects the airbag system.

Q: How do I reset the airbag light?
A: After repairs, use an OBD-II scanner to clear the codes and reset the airbag system.

Last updated: Jun 8, 2026 • Source: internal database

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