Powertrain, generic · Vehicle speed, idle control and auxiliary inputs

P05B8 Restraint Deployment Signal Circuit/Open

Check engine lightUsually off
EmissionsNot relevant
Drive cycleNot required
Limp modeNo

After a crash the restraint control module tells the engine module that airbags or belt tensioners have fired; the engine module then cuts the fuel pump (Ford: until the ignition is cycled) and possibly the engine. Depending on the maker the message travels over CAN and/or a dedicated wire with a defined level or voltage drop. P05B8 means the wired signal line is open – no valid rest level arrives. After a real crash the fuel cut-off may then not be triggered via this line. No manufacturer document available to us uses this code; it is a safety function, not an emission-relevant monitor, so usually without warning lamp.

Likely causes

Signal wire or connector between restraint and engine module open (e.g. after accident repair or seat removal)
Corroded or spread pin at either module
Replacement module not configured
Restraint module output stage

Symptoms

  • Code stored, driving usually normal
  • Possibly message that fuel cut-off is unavailable
  • No check engine light

Repair estimate

DifficultyMediumWorkshop job
Parts and labour€80–300
Time0.5–2 h

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

Parts involved

restraint control modulecrash signal wiringengine control module

Related codes

P05B9P05BAP05BBP0230P0627U0151

References: static.nhtsa.gov, patents.google.com, law.cornell.edu.