Powertrain, generic (extended)

P25BA Regeneration Control Switch Circuit/Open

Check engine lightOn
EmissionsRelevant
Drive cycleNot required
Limp modeNo

P25BA concerns the dash or panel switch with which the driver starts, or on some trucks blocks, a diesel particulate filter regeneration. The engine controller reads the switch as a discrete input and sets this code when the circuit is open or otherwise unusable, so a press no longer reaches it. Volvo describes a rocker of this kind: one half inhibits automatic regeneration below 40 km/h, the other starts a parked regeneration with the truck stationary, parking brake set, gearbox in neutral and engine warm. GM's L5P trucks with option FPF instead use the exhaust brake switch for the same job (bulletin 20-NA-203). No manufacturer documents P25BA publicly. Automatic regeneration while driving continues, but a requested parked regeneration cannot be started and soot can build up.

Likely causes

Switch connector loose or unplugged behind the dash
Broken signal or reference wire to the switch
Internal open circuit in the regeneration switch

Symptoms

  • Parked regeneration cannot be started when the cluster asks for it
  • Filter or regeneration warning lamp stays on longer than usual
  • Check engine lamp

Repair estimate

DifficultyEasyDIY possible
Parts and labour€40–300
Time0.3–1.5 h

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

Parts involved

regen request switchwiring harness

Related codes

P25BBP25BCP2459

References: stpi.it.volvo.com, static.nhtsa.gov, law.cornell.edu.