OBD-II trouble code
B0030: Second Row Left Side Airbag Deployment Control (Subfault)
A firing-loop fault on the second-row left side airbag. A side bag has almost no time to work, which is why it is single-stage — and why the seat it lives in is the thing most likely to have broken its circuit.
Quick facts
- System
- Body
- Category
- Airbag / SRS Restraints
- Severity
- High severity
- Drivable
- Usually safe to drive short-term
- Repair cost range
- $120 – $950
- DIY difficulty
- Shop recommended
What does B0030 mean?
B0030 is recorded by the restraints module when the firing circuit for the side airbag at the second-row left seat measures outside the narrow window these loops must stay within. The vehicle continues to drive normally; what is impaired is protection in a side impact.
A side airbag is not simply a smaller frontal airbag, and understanding why explains most of this code. In a frontal collision there is an engine bay and a substantial crush structure between the impact and the occupant, which buys the restraints system tens of milliseconds to sense, decide and inflate. In a side impact there is a door skin, a trim panel and very little else. The bag has to be fully inflated in a few thousandths of a second. There is no time to fire anything in stages, which is why side airbags are single-stage devices with a single loop — if you are looking for stage codes at this position, none exist, and their absence is not a sign that something is missing.
Where the bag lives is the other half of the picture. On most vehicles the second-row side airbag is built into the outer bolster of the seat back rather than into the door or the body. That means the firing loop has to travel from the floor, up through the seat frame, across the recline mechanism and into a moving structure. It flexes every single time somebody reclines the backrest, slides the seat, folds it forward or tumbles it out of the way. No other restraints circuit on the vehicle is articulated the way this one is, and fatigue at the flex point is a genuine failure mode rather than a theoretical one.
That location also puts the loop directly in the path of work done to the seat rather than to the restraints system. Retrimming and reupholstery, seat heater retrofits, child-seat installation, cleaning after spills, and seat removal for carpet or floor repair all involve handling the same connector and the same loom. The most common single offender is aftermarket seat covers. Fitting them means working around the connector and the loom, and it introduces a second and more serious problem that has nothing to do with the code: a cover that is not specifically designed and certified for a side-airbag seat can stop the bag tearing out through the seam at the moment it needs to. That is worth raising with any owner who has them fitted, regardless of what caused the fault.
One more thing follows from the geometry. This is the seat directly behind the driver, on the traffic side of the vehicle in left-hand-drive markets, and it is the rear seat adjusted most often — moved forward for legroom in front, folded for loads, tumbled for access. Frequency of movement and frequency of loop flexing go together.
Firing circuits contain live pyrotechnics and are measured with current-limited equipment. The system must be safely powered down by someone following the manufacturer's procedure before any of it is opened up.
Common causes
- Fatigue fracture in the loop where it crosses the seat back recline mechanism, from repeated adjustment
- Connector under the seat disturbed or unlatched during seat removal, cleaning or carpet work
- Damage caused while fitting aftermarket seat covers over a side-airbag seat back
- Loom pinched or cut during a seat heater retrofit or reupholstery job
- Corroded under-seat connector after a spill or a wet footwell on the traffic side of the vehicle
- Open or out-of-specification squib in the seat-mounted side airbag module
- Loop trapped under the seat rail after the seat was refitted without routing the harness correctly
- Restraints module configured for side airbags the vehicle was not built with
- Failed drive circuit inside the restraints control module, established last
Symptoms
- Airbag warning lamp illuminated continuously
- B0030 stored with a symptom byte identifying open, shorted or out-of-range
- Fault that appears or disappears as the second-row left backrest is reclined or the seat is moved
- Fault dating from seat removal, retrimming, a heater retrofit or seat cover fitting
- Aftermarket seat covers fitted over a seat that carries a side airbag
- Damp or stained carpet under the second-row left seat
- No stage-numbered companion codes, because a side airbag has only one firing stage
- Engine, transmission and driving behaviour entirely unaffected
Diagnostic steps
- 1.Confirm the vehicle was built with second-row side airbags and that the restraints module's configuration matches, before treating the code as a wiring fault.
- 2.Ask what has been done to this seat — removal, retrimming, a heater retrofit, cleaning, covers — since work on the seat is the leading route to this fault.
- 3.Remove any aftermarket seat covers and inspect the bolster seam and the loom beneath, and advise the owner about covers on a side-airbag seat regardless of the outcome.
- 4.Power down and discharge the restraints system to the manufacturer's procedure before disconnecting anything.
- 5.Check the under-seat connector for latching, backed-out terminals, corrosion and evidence of a wet footwell.
- 6.Trace the loop from the floor up through the seat frame and across the recline mechanism, looking specifically for fatigue at the flex point rather than for chafe.
- 7.Recline, slide, fold and tumble the seat through its full range while monitoring, because an articulated circuit shows its fault in motion and not at rest.
- 8.Confirm the loom is routed clear of the seat rails and has not been trapped when the seat was refitted.
- 9.Measure the loop resistance with approved current-limited restraints test equipment, never with a general-purpose multimeter.
- 10.After repair, clear the codes, run the module self-test and verify the lamp stays out through several seat adjustments and ignition cycles.
Repair cost
$120 – $950
Reseating or re-terminating the under-seat connector runs $150 to $380. Repairing the loop where it has fatigued across the recline mechanism is $200 to $480, because the seat generally has to come out and the trim off to reach it. A seat-mounted side airbag module is $250 to $700 in parts, and on many designs the seat back cover and foam have to be disturbed to fit it, pushing the total toward $950. Restraints module replacement with programming is at the top of the range. Diagnosis is $110 to $220. If aftermarket covers are fitted, budget for replacing them with airbag-compatible ones or removing them entirely.
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.