OBD-II trouble code
B0043: Third Row Left Frontal Stage 3 Deployment Control (Subfault)
The restraints module found a third-row left frontal airbag firing circuit out of specification. What makes this different from the same fault further forward is distance: this loop is at the end of the longest restraints wiring run in the vehicle.
Quick facts
- System
- Body
- Category
- Airbag / SRS Restraints
- Severity
- High severity
- Drivable
- Usually safe to drive short-term
- Repair cost range
- $150 – $1,400
- DIY difficulty
- Shop recommended
What does B0043 mean?
The restraints control module measures the resistance of every pyrotechnic loop it owns and stores a code when one falls outside the narrow band it will accept. B0043 identifies that loop as belonging to a third-row left frontal airbag, and the symptom byte accompanying the code names the specific electrical condition — open, shorted to power, shorted to ground, or simply out of range.
The restraints module lives near the centre of the vehicle, usually under the console or beneath the front seats. Everything it fires is reached by wire from there, and the third row is the furthest thing from it. That length is the defining fact about this code. The harness has to travel the entire length of the floor pan, generally routed under the sill trim or beneath the carpet, past every door aperture, through the area where the rear wheel arch intrudes, and out to a connector at the very back of the passenger compartment. Every one of those is a place where wiring gets pinched, soaked, walked on or cut.
The consequences follow directly. Third-row restraint circuits fail from mechanical and environmental damage far more often than from component failure, which is close to the reverse of the pattern at the front of the vehicle. Water is the leading offender: a blocked sunroof drain, a leaking tailgate or rear light seal, or a failed rear door membrane puts water into the lowest part of the floor, which is exactly where this harness runs, and a soaked connector reads as a low-resistance fault long before it looks corroded from the outside. Rear footwells also flood first, and they dry last.
The second offender is the seat itself. Third-row seats are built to fold, tumble or drop into the floor, so their harness is designed to move — and everything that moves eventually fatigues. On top of that, the folded third row is where people put cargo, so the connectors underneath spend their lives being loaded on, dragged over, and occasionally struck by whatever was thrown in the back. A third-row circuit that has never been touched by a technician can still have been damaged a hundred times by ordinary use.
The practical result is that a technician should search this circuit along its length rather than starting at the ends. On a front airbag it is reasonable to check the connector, check the bag, and be done. Here, the fault is statistically more likely to be somewhere in the middle of a very long run, and the fastest route to it is usually to look for evidence of water in the rear footwell and cargo area before reaching for a meter at all.
Common causes
- Water intrusion into the rear floor or cargo area from a blocked drain, leaking tailgate seal or failed door membrane
- Harness damage along the floor run, under sill trim or beside the wheel arch, from cargo, luggage or trim removal
- Connector at the third row crushed or dragged by loaded cargo on a folded seat
- Wiring fatigue where the harness flexes as the third-row seat folds, tumbles or stows into the floor
- Corroded terminals from salt and moisture carried in on footwear and left in the rear footwell
- Failed initiator in the airbag assembly
- Shorting bar not releasing at the airbag connector after service
- Damage from a rear-end collision repair, aftermarket tow bar wiring or rear entertainment installation sharing the same route
- Failed restraints module driver for this loop
Symptoms
- Airbag or SRS warning light on and staying on
- B0043 stored in the restraints module with a symptom byte naming the fault type
- Fault appearing after wet weather, a car wash, or a period with a leaking seal
- Fault appearing after the third row has been folded, stowed or loaded with cargo
- Other rear restraints codes present, suggesting shared harness damage rather than a single failed part
- No effect on engine operation or driving whatsoever
- Damp carpet or a musty smell in the rear footwell or cargo area
Diagnostic steps
- 1.Check the rear footwell and cargo area for damp carpet, water staining or a musty smell before doing any electrical testing. Water is the leading cause on this particular circuit and finding it first reframes the whole job.
- 2.Look for the source of any water — blocked sunroof or pillar drains, tailgate and rear lamp seals, and rear door membranes are the usual suspects — because repairing the circuit without stopping the leak guarantees a repeat.
- 3.Record the full symptom byte. A short to ground on this circuit is often literally water, while an open is more often physical damage, and the byte points you at which story to pursue.
- 4.Note whether other third-row or rear restraints codes are also stored. Several codes from the same end of the vehicle point at shared harness damage along the run rather than at individual failed components.
- 5.Disable the restraints system to the manufacturer's procedure and observe the specified waiting period before disconnecting anything.
- 6.Inspect the harness along its full length rather than only at the ends — under sill trim, beside the wheel arch, and where it crosses into the rear of the cabin. On this circuit the fault is more often in the middle of the run than at either termination.
- 7.Fold, tumble and stow the third-row seat while monitoring the circuit, since the section that flexes with seat movement is a specific fatigue point that a static test will not find.
- 8.Check for aftermarket wiring sharing the route. Tow bar electrics, rear entertainment and cargo-area accessories are frequently routed along the same path and are a recurring source of damage.
- 9.Measure loop resistance against the manufacturer's figure with an approved airbag meter only, and repair wiring and water ingress before considering the airbag assembly.
Repair cost
$150 – $1,400
This code tends to cost more than the same fault at the front of the vehicle, and the reason is access rather than parts. Tracing a fault along a floor-length harness means lifting sill trim and often carpet, so diagnostic time alone runs $150 to $400. Repairing the wiring once found is comparatively cheap. If water is the cause, the leak has to be fixed too, which adds $150 to $600 depending on whether it is a blocked drain or a failing seal — and skipping that step means doing the whole job again. A failed third-row airbag assembly with the trim work to reach it lands between $600 and $1,400. Because water and physical damage dominate here, the wiring inspection genuinely deserves to happen before any part is ordered.
Estimate your repair
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Open the Repair Cost Estimator with wiring harness / circuit repair 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.