OBD-II trouble code
B0031: Second Row Left Frontal Stage 1 Deployment Control (Subfault)
The airbag/SRS control module detected an electrical fault in the second-row left frontal Stage 1 airbag deployment loop. That 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 B0031 mean?
B0031 is a body (B) code stored by the airbag control module. Its SAE-generic definition is 'Second Row Left Frontal Stage 1 Deployment Control,' referring to the first-stage firing loop for the frontal airbag protecting the left-side second-row (rear) seating position. Some vehicles — particularly larger SUVs, minivans, and vehicles built for markets that require rear frontal or seat-cushion airbags — protect rear occupants with staged frontal airbags. 'Stage 1' is the first, typically softer deployment charge; a matching 'Stage 2' loop (B0032) fires the fuller charge in a more severe crash. As with all B-codes, confirm the exact application against your make's service data, since not every vehicle has a second-row frontal airbag.
The module sets the code when the Stage 1 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 the airbag serves a rear seat, its firing loop and connector run under the seat or through the seat frame, where the connector flexes as the seat is adjusted, folded, or removed — the most common place these faults originate.
This is a supplemental restraint fault, not a driveability fault: the vehicle drives normally, but the second-row left 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 under the second-row left seat
- Damaged wiring in the Stage 1 firing loop after seat removal, folding, or cargo damage
- Failed second-row frontal airbag inflator (squib)
- Fault in the SRS connector or its shorting bar at the airbag
- Prior collision or repair that disturbed the rear-airbag loop
- Faulty airbag/SRS control module
Symptoms
- Airbag / SRS warning light on
- Stored B0031 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 second-row seat is moved or folded
Diagnostic steps
- 1.Use a scan tool that can access the airbag/SRS module and record B0031 with its full symptom byte and any companion codes.
- 2.Confirm that the vehicle has a second-row left frontal airbag and locate its connector, since rear frontal airbags vary widely by make and market.
- 3.With the system safely disabled per service procedure, inspect the under-seat connector and seat-frame harness for corrosion, backed-out terminals, or crush damage.
- 4.Fold and adjust the seat while watching for an intermittent fault, since these loops are commonly disturbed by seat movement or recent seat service.
- 5.Measure the Stage 1 loop resistance against specification to separate a wiring/connector fault from a failed inflator.
- 6.If both B0031 and B0032 are set, focus on the shared connector and airbag rather than two separate stage failures.
- 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 under-seat connector can be inexpensive, while a failed rear airbag or control module is much costlier. SRS diagnostic time typically runs $100-$200, and a second-row 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.