Powertrain, generic (extended)

P25FB Turbocharger/Supercharger Bypass Valve C Control Circuit Range/Performance

Check engine lightOn
EmissionsRelevant
Drive cycleRequired
Limp modeNo

P25FB is set when the control circuit of bypass valve C is not open or shorted, but its electrical behaviour does not match the command – for instance a current that rises too slowly or settles at the wrong level, or a signal that drops out now and then. That points to a coil whose resistance has changed with heat, contact resistance in the connector, or a valve whose armature moves sluggishly and so alters the current curve. Pure circuit faults are reported as P25F8 to P25FA, a valve that is mechanically stuck as P25FC. Which compressor valve C belongs to is decided by the manufacturer, and none documents this code publicly; CARB requires output components to be checked for proper function. Consequences range from surging on lift-off to reduced boost.

Likely causes

Valve coil resistance changed by heat ageing
Contact resistance or moisture in the valve connector
Sluggish valve armature due to deposits

Symptoms

  • Check engine lamp on
  • Occasional fluttering on lift-off
  • Uneven boost build-up

Repair estimate

DifficultyMediumWorkshop job
Parts and labour€50–600
Time0.5–3 h

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

Parts involved

bypass valve cbypass solenoid

Related codes

P25F8P25F9P25FAP25FCP0039P00C3

References: law.cornell.edu, ms-motorservice.com, en.wikipedia.org.