Body, generic

B004B Third Row Right Frontal Stage 3 Deployment Control

Check engine lightUsually off
EmissionsNot relevant
Drive cycleNot required
Limp modeNo

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.

Likely causes

Damaged stage 3 lead or squib
Restraint module configured for equipment the vehicle does not have (wrong part or coding)
Loose connector in the second-row seatback

Symptoms

  • 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

Repair estimate

DifficultyShop_onlyWorkshop job
Parts and labour€100–1,200
Time1–4 h

Typical range across vehicles; the real cost depends on what the testing finds.

Parts involved

third row right frontal airbagsquib circuitsrs seat wiringsrs control module

Related codes

B0049B004AB0043

References: static.nhtsa.gov, patents.google.com, patents.google.com.