OBD-II trouble code
B003B: Second Row Right Frontal Stage 3 Deployment Control (Subfault)
The restraints module cannot verify the third-stage firing loop of the second-row right frontal airbag. Before chasing wiring, establish whether this vehicle was actually built with a three-stage inflator at that position — many were not.
Quick facts
- System
- Body
- Category
- Airbag / SRS Restraints
- Severity
- High severity
- Drivable
- Usually safe to drive short-term
- Repair cost range
- $120 – $1,100
- DIY difficulty
- Shop recommended
What does B003B mean?
B003B is stored by the restraints control module against the highest-force firing stage of a frontal airbag serving the right-hand second-row seat. The last character is the hexadecimal letter B, not a digit, so B0039, B003A and B003B are three consecutive values describing stages one, two and three of the same inflator.
The first thing this code demands is a question about the vehicle rather than a measurement. Frontal airbags for rear seating positions are unusual to begin with, and three-stage frontal inflators at a rear position are rarer still — they belong to a small population of larger vehicles, extended and converted bodies, and high-specification cabins where the manufacturer wanted very fine control of deployment force for rear occupants. Restraints modules are written for a platform and then configured for an individual build, and that configuration is data, not hardware. A module that has been replaced, reflashed, cloned or taken from a donor vehicle can be expecting a third stage that this car was never fitted with. It will then measure an open loop, faithfully and permanently, and there is nothing physical to repair. Confirming the build specification and the module's configuration before touching a connector is the step that saves the most wasted labour on this particular code.
Where the third stage genuinely exists, its rarity has a second consequence that matters on used vehicles. Stage three is the tier the system reaches for least often, so it is also the one most easily overlooked in a repair history. A vehicle that went through a moderate impact may have had a partial deployment, been put back together, and passed back into service with an inflator whose remaining stage nobody accounted for properly. A solitary stage three code on a car with any collision history is a reason to establish exactly which inflator part number is fitted and whether it matches what the module expects, rather than to assume a wire has chafed.
The seating position adds its own pattern. In left-hand-drive markets the right-hand second-row seat is the kerb-side seat: the one used for loading, the one children are put in and out of, and the position where child restraints are most often anchored. That means repeated seat folding for access, repeated tugging at anchor points, and repeated disturbance of whatever sits beneath the cushion. Connectors under this seat are handled more often than those under any other rear position, and they show it.
As with any restraints fault, the vehicle drives normally and the deficiency is entirely in what happens during a collision. Firing loops contain pyrotechnic devices, and the system must be safely powered down by someone who knows the make-specific procedure before any connector is opened.
Common causes
- Restraints module configured for a three-stage inflator the vehicle was not built with, after module replacement, reflash or a donor transplant
- Incorrect or non-matching inflator fitted during a previous collision repair
- Connector beneath the second-row right seat disturbed by repeated folding for kerb-side access
- Terminal backed out or spread at the seat connector after child-restraint anchoring work
- Open or high-resistance stage three squib inside the inflator
- Corrosion in the under-seat connector from spilled drinks or wet footwells at the loading door
- Harness damage from cargo or child-seat hardware bearing on the loop under the cushion
- Failed output stage in the restraints control module, established only after the build specification is confirmed
Symptoms
- Airbag warning lamp illuminated and staying on
- B003B stored with a symptom byte identifying open, shorted or out-of-range
- Code that will not clear and returns immediately after every reset attempt
- Fault present since a restraints module was replaced or reprogrammed
- Fault present since a collision repair involving rear seating
- Code that comes and goes as the second-row right seat is folded for access
- Stage one and stage two loops reporting healthy while stage three does not
- No effect whatsoever on how the vehicle starts, idles or drives
Diagnostic steps
- 1.Establish the vehicle's actual build specification first and confirm that a three-stage frontal inflator exists at the second-row right position, because a substantial share of these codes are configuration faults with no hardware to repair.
- 2.Check whether the restraints module has ever been replaced, reprogrammed or taken from a donor vehicle, and verify its configuration matches the build.
- 3.Record the full symptom byte and note whether B0039 and B003A are healthy — a solitary stage three fault points at that stage's own squib or terminals rather than at anything shared.
- 4.Review collision history and confirm the fitted inflator part number matches what the module expects, since partial deployments and mismatched replacements are common on this stage.
- 5.Disable and discharge the restraints system following the manufacturer's procedure before opening any connector.
- 6.Inspect the under-seat connector for backed-out terminals, spread contacts and corrosion, paying attention to damage consistent with child-seat hardware and repeated folding.
- 7.Fold, slide and latch the seat through its full range while monitoring for an intermittent, since this is the rear position handled most often.
- 8.Measure the stage three loop resistance against specification with the approved tooling, never with an ordinary multimeter.
- 9.Substitute the module's configuration or the inflator only after the wiring and connector have been cleared.
- 10.Clear the codes, re-run the module self-test and confirm the lamp extinguishes and stays out over several ignition cycles.
Repair cost
$120 – $1,100
Correcting a module configuration that expects hardware the vehicle does not have is the cheapest genuine outcome at $120 to $280, and it is a realistic outcome on this code specifically. Repairing or re-terminating the under-seat connector is $150 to $400. A rear frontal inflator is not sold by the stage, so condemning stage three means buying the whole assembly — $350 to $900 in parts on the applications that use one, with fitting on top. Restraints module replacement with programming runs $400 to $1,100. Diagnostic time is $110 to $220 and is worth paying for here rather than guessing, because the configuration question has to be settled before any part is justified.
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.