Body, generic

B003B Second Row Right Frontal Stage 3 Deployment Control

Check engine lightUsually off
EmissionsNot relevant
Drive cycleNot required
Limp modeNo

B003B is the third firing element of the right rear-seat frontal airbag. In front airbags Mercedes-Benz uses this third position for the squib that opens a vent valve and lets gas escape (B000313 driver, B001213 passenger); a patent from Breed shows the other option, a third gas chamber with its own igniter that the controller can fire later, for example in a second impact. Which of these a rear bag would use is not published, and no carmaker documents B003B. If it is stored, the module has found the third element out of range in resistance or voltage. Stage 1 and 2 of the same bag report as B0039 and B003A. The airbag lamp stays on.

Likely causes

Loose or corroded connector of the airbag lead routed through the front seat backrest
Damaged stage 3 lead or vent squib in the right rear airbag
Restraint module configured for equipment the vehicle does not have (wrong part or coding)

Symptoms

  • Airbag warning lamp on
  • Right rear airbag may deploy without its adaptive third stage
  • 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

second row right frontal airbagsquib circuitsrs seat wiringsrs control module

Related codes

B0039B003AB0033

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