OBD-II trouble code
B004A: Third Row Right Frontal Stage 2 Deployment Control (Subfault)
The airbag/SRS control module detected an electrical fault in the third-row right frontal airbag's stage 2 deployment loop. That rear frontal airbag may not deploy as designed, so this needs prompt professional attention.
Quick facts
- System
- Body
- Category
- Airbag / SRS Restraints
- Severity
- High severity
- Drivable
- Usually safe to drive short-term
- Repair cost range
- $100 – $900
- DIY difficulty
- Shop recommended
What does B004A mean?
B004A is a body (B) code stored by the airbag control module. It is a hexadecimal code — the character after B004 is the letter A, not a number — and its SAE-generic definition is 'Third Row Right Frontal Stage 2 Deployment Control,' referring to the firing loop that deploys the second stage of a frontal airbag protecting the right-side third-row seating position. It is the stage 2 companion of B0049 (Stage 1) and the right-side mirror of B0042 (Third Row Left Frontal Stage 2). A third-row frontal airbag is uncommon — very few vehicles are equipped with one — so this code is rare, and you should confirm the exact application against your make's service data before assuming the airbag is fitted. Multi-stage airbags fire in steps so the module can tailor deployment force to crash severity; stage 2 adds force beyond the softer stage 1 for more severe impacts.
The module sets the code when the stage 2 deployment loop's resistance falls outside the tight window these pyrotechnic circuits require — an open circuit, a short to power or ground, or resistance that is too high or too low. A symptom byte appended to the code identifies the exact fault type. Because a third-row airbag's firing loop runs through connectors near the rear of the cabin that are easily disturbed by folding the seats, loading cargo, or trim service, those connectors and any harness disturbed during rear-area work are the most common trouble spots. If both B0049 and B004A set together, the shared connector, ground, or airbag is a more likely cause than two independent stage failures.
This is a supplemental restraint fault, not a driveability fault: the vehicle drives normally, but the third-row right frontal airbag may not deploy as intended in a crash, and airbag circuits carry a small risk of unintended deployment when mishandled. SRS diagnosis and repair should be performed by a qualified technician who can safely disable the system, and the fault should not be left unrepaired.
Common causes
- Corroded, backed-out, or loose connector near the third-row right seat
- Damaged wiring in the rear frontal-airbag loop after seat folding, removal, or cargo damage
- Failed third-row frontal airbag inflator or its stage 2 squib
- Fault in the SRS connector or its shorting bar at the airbag
- Prior frontal-impact damage or repair that disturbed the loop
- Faulty airbag/SRS control module
Symptoms
- Airbag / SRS warning light on
- Stored B004A fault (often with a symptom byte) in the restraints module
- No effect on engine or driving performance
- Fault that may appear or clear as the third-row seat is folded or moved
Diagnostic steps
- 1.Use a scan tool that can access the airbag/SRS module and record B004A with its full symptom byte and any companion codes such as B0049.
- 2.Confirm the vehicle actually has a third-row frontal airbag — it is uncommon — and locate its connector for the specific make and model.
- 3.With the system safely disabled per service procedure, inspect the rear connector and the seat-frame harness for corrosion, backed-out terminals, or crush damage.
- 4.Fold and adjust the third-row seat while watching for an intermittent fault, since these loops are commonly disturbed by seat movement or cargo loading.
- 5.Measure the deployment-loop resistance against specification to separate a wiring/connector fault from a failed inflator.
- 6.If both stage codes (B0049/B004A) are present, focus on the shared connector, ground, and the airbag itself rather than two separate squibs.
- 7.Repair the wiring/connector fault or replace the indicated component, then clear codes and confirm the SRS light stays off.
Repair cost
$100 – $900
Reseating or repairing the rear connector can be inexpensive, while a failed airbag or control module is much costlier. SRS diagnostic time typically runs $100-$200, and a third-row frontal airbag or SDM/RCM replacement with programming can reach several hundred dollars or more. SRS work should be done by a qualified technician.
Estimate your repair
Run the numbers for your vehicle
Open the Repair Cost Estimator with airbag control module (sdm) replacement / reset preselected. Adjust labor rate and vehicle category to fit your situation.
DIY vs shop
Leave this one to a qualified shop. It typically involves emissions-critical components, refrigerant handling, or other work that requires manufacturer-grade tooling, training, or certification. DIY attempts often produce a more expensive problem than the original code.