B004B code meaning
Third Row Right Frontal Stage 3 Deployment Control
What B004B means
B004B is the last code of the third-row frontal block: stage 3 of the right-hand bag. What a third element does is up to the maker. Mercedes-Benz shows one answer in its front airbags, where the third slot is a vent valve squib (B000313, B001213); Breed's patent shows another, a third chamber held back for a later second impact. Mercedes-Benz's rear airbag filing also links an extra chamber to the first through valves or throttles. No vehicle maker documents B004B and no NHTSA bulletin contains it. A fault here leaves the bag without its third element; stage 1 and 2 are B0049 and B004A. Airbag lamp on.
B004B at a glance
- Check engine lightUsually not
- Emissions testNot an emissions code
- Limp modeNot expected
- Repair difficultyWorkshop only
- Typical labor1 to 4 hours
- Clears after repairWhen cleared with a scanner
Symptoms of B004B
- Airbag warning lamp on
- Right third-row airbag may deploy without its third element
- Safety note: do not probe the airbag circuit yourself; unplug airbag connectors only with the battery disconnected and the stated wait time observed
Common causes of B004B
- PossibleDamaged stage 3 lead or squib
- Less likelyRestraint module configured for equipment the vehicle does not have (wrong part or coding)
- Less likelyLoose connector in the second-row seatback
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
Third row right frontal airbagSquib circuitSRS seat wiringSRS control module
What each part of B004B means
| B | Body system: airbags, seat belts, power seats, lights and climate control. |
| 0 | Generic code: it means the same on every make (SAE standard). |
| 4B | The exact fault in that area. |
What to do next
- Note B004B and any other codes stored with it: several codes together often point to one cause.
- Check for loose connectors and damaged wiring around the parts the code names.
- Check open recalls for your car: some faults are fixed for free by the dealer. Enter your VIN.
- Clear the code only after the repair. If it comes back, the fault is still there.
Buying a used car? Scan it for stored codes before you pay. A recently cleared memory can hide a problem.
Questions about B004B
What does B004B mean?
B004B means "Third Row Right Frontal Stage 3 Deployment Control". B004B is the last code of the third-row frontal block: stage 3 of the right-hand bag. It is a generic code, so it means the same on every make.
Is it safe to drive with B004B?
B004B does not normally turn on the check engine light by itself. Watch for the symptoms above and have it checked soon.
Will B004B fail an emissions test?
B004B is not an emissions code, so on its own it usually does not fail an emissions test. Other stored codes or a lit check engine light still can.
How hard is B004B to fix?
Difficulty: workshop only. A typical repair takes 1 to 4 hours of work. This is a job for a workshop.
Will B004B clear itself after the repair?
Clear the code with a scanner after the repair. If the fault is fixed, it does not come back.