Powertrain, generic (extended)

P25F8 Turbocharger/Supercharger Bypass Valve C Control Circuit

Check engine lightOn
EmissionsRelevant
Drive cycleNot required
Limp modePossible

Bypass valves in the intake let charge air flow around a compressor: on turbo engines they are the recirculation valves that open on a sudden throttle lift so the compressor does not surge, and on engines with a supercharger they can route air past the blower while it is idling or uncoupled. A third such valve, C, only appears on systems with several compressors; which valve gets the letter is manufacturer-specific. P25F8 is the general fault of its control circuit, typically an open circuit. No manufacturer documents P25F8. For valve A, Saab's GM-based 2.0 litre watches for open, short to ground or short to voltage for longer than 10 s at 11–32 V supply and sets a type B code. Expect surging noises on lift-off or less boost.

Likely causes

Broken wire or loose connector at bypass valve C
Open coil in the valve or its solenoid
Supply voltage missing (fuse, main relay)

Symptoms

  • Check engine lamp on
  • Fluttering noise when lifting off the throttle
  • Less boost or slower response

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 solenoidwiring harness

Related codes

P25F9P25FAP25FBP25FCP0033P00C0

References: law.cornell.edu, saabwisonline.com, ms-motorservice.com, mobilityengineeringtech.com.