OBD-II trouble code
B004B: Third Row Right Frontal Stage 3 Deployment Control (Subfault)
A fault on the third stage of a multi-stage deployment device. The single most informative thing about this code is what else is stored alongside it: all stages of one device share a connector and a harness branch, so one stage faulting alone means the squib, and every stage faulting together means the wiring.
Quick facts
- System
- Body
- Category
- Airbag / SRS Restraints
- Severity
- High severity
- Drivable
- Usually safe to drive short-term
- Repair cost range
- $100 – $1,200
- DIY difficulty
- Shop recommended
What does B004B mean?
A stage is a separate pyrotechnic charge inside one device. Multi-stage deployment exists so the restraints module can decide not merely whether to fire, but how hard — using crash severity, occupant weight where the vehicle measures it, and seat belt status to choose how much gas to release. Two stages are common. Three are not, and a vehicle that can report a stage 3 fault has a comparatively sophisticated restraint design, which in itself is worth confirming against service data rather than assuming.
The fact that makes this code diagnosable rather than merely alarming is a physical one about how stages are wired. Every stage of a single device is fired through the same connector at that device, and the wires for those stages travel together in the same harness branch for essentially the whole of their route back to the module. Nothing separates them until the last few inches. That has a direct and reliable consequence for reading fault patterns. If the harness were crushed, chafed, soaked or corroded anywhere along its run, it could not selectively damage one stage while leaving the others intact — all the stages for that device would fault at once. So a stage 3 fault standing alone, with stages 1 and 2 reporting healthy, is strong evidence that the problem is in the last few inches: the individual squib for that stage, or its own pin in the shared connector. Conversely, a stage 3 fault arriving together with stage 1 and stage 2 faults for the same device tells you not to look at the device at all, because the common factor is the wiring or the connector body they share. Reading which of those two patterns you have, before touching anything, narrows the job more than any measurement will.
The module's response to a stage fault is worth understanding because it is often misjudged. Losing one stage is not a partial loss of protection with two thirds still available. A module that cannot verify every stage of a device generally declines to deploy that device at all, because it can no longer guarantee it will deliver the force its deployment strategy calculated. The safe default is not to fire an unverifiable pyrotechnic. So a stage 3 fault should be treated as the device being unavailable rather than as the device being slightly reduced.
There is a cost consequence that follows directly from the same physical fact. Stages are charges within one sealed assembly and are not separately serviceable. There is no stage 3 to buy. If the fault is genuinely in the squib, the entire device is replaced regardless of how healthy the other stages are — which is precisely why it is worth spending the time to prove the fault is not simply a corroded pin in the shared connector, because those two conclusions differ by an order of magnitude in price.
Common causes
- Failed squib for that individual stage inside the device, which is the leading cause when the other stages report healthy
- Corroded or backed-out pin for that stage within the shared connector at the device
- Connector not fully latched, disturbing one terminal more than the others
- Damaged harness branch, which typically faults all stages of the device together rather than one
- Water intrusion into the connector body, which usually affects several stages at once
- Restraints module configured for a three-stage device when the vehicle was built with a two-stage one, producing a permanent open on a stage that does not exist
- Previous restraint repair that fitted a device with a different stage count from the original
- Damage during rear seat removal, refitting or trim work
- Restraints control module output fault on that specific channel
Symptoms
- Airbag or SRS warning light on and staying on
- B004B stored with a symptom byte, most often an open circuit or out-of-range resistance
- Stage 1 and stage 2 loops for the same device reporting healthy, which localises the fault to the squib or its pin
- Several stage codes for the same device stored together, which instead points at the shared connector or harness
- The device disabled entirely rather than partially, since the module will not fire what it cannot verify
- No effect on how the vehicle drives
- Fault present continuously since a previous restraint repair or module replacement
Diagnostic steps
- 1.Read every restraint code before doing anything else and note which stages of this device are implicated. That pattern is the most informative evidence available on this code and it costs nothing to gather.
- 2.Interpret the pattern deliberately. All stages of one device share a connector and a harness branch, so one stage faulting alone means the squib or its individual pin, while all stages faulting together means the wiring or the connector body.
- 3.Confirm from service data that this vehicle was actually built with a three-stage device. A module configured for more stages than the hardware has reports a permanent open on the stage that does not exist.
- 4.Ask whether any restraint component or module has been replaced. A device fitted with a different stage count from the original produces exactly this fault and no amount of wiring work will clear it.
- 5.Disable the restraint system by the manufacturer's procedure and observe the specified waiting period before opening any connector.
- 6.Inspect the shared connector at the device with a light, checking each terminal individually rather than the connector as a whole. A single backed-out or corroded pin is the cheap version of this fault.
- 7.Confirm the connector is fully latched and its lock engaged, since a partially seated connector loads some terminals more than others.
- 8.Measure the stage 3 loop against the manufacturer's specification and compare the result against the readings for the other stages of the same device.
- 9.Accept before quoting that stages cannot be replaced individually. If the squib is confirmed faulty, the whole device is the repair.
Repair cost
$100 – $1,200
The price gap on this code sits between a terminal and an assembly, so it is worth resolving carefully. A connector or terminal repair, once diagnosed, is often $150 to $400 including the access work. A harness branch repair is $200 to $500. If the squib itself has failed, there is no stage to buy on its own — the complete device is replaced, commonly $600 to $1,200 fitted for a rear seating position where access is poor. A configuration correction after a mismatched device or module was fitted may cost no more than the diagnostic charge of $100 to $250. Proving whether the fault is a pin or a squib before ordering anything is the difference between the two ends of that range.
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.