Powertrain, generic (extended)

P25BC Regeneration Control Switch Circuit High

Check engine lightOn
EmissionsRelevant
Drive cycleNot required
Limp modeNo

P25BC is the high-voltage counterpart: the regeneration switch line carries a level near supply voltage that no switch position can produce. A wire chafed against a battery or ignition feed, water in a switch connector or a switch whose internal resistor network has failed are plausible causes. If the switch requests regeneration by pulling the line up, a stuck high could resemble a permanent start command. That matters because a parked regeneration raises idle speed and exhaust temperature sharply; GM bulletin 20-NA-203 tells drivers to stand on level ground outdoors, clear of anything that can burn. Without a reliable switch the engine controller has to rely on automatic regeneration while driving. No manufacturer documents P25BC publicly, so repair follows the vehicle's wiring diagram.

Likely causes

Switch signal wire shorted to battery or ignition voltage
Moisture in the switch connector
Internal fault in the switch or its resistor network

Symptoms

  • Regeneration switch ignored by the engine controller
  • Unexpected regeneration messages in the cluster
  • 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

P25BAP25BBP2459

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