P25F9: Turbocharger/Supercharger Bypass Valve C Control Circuit Low

P25F9 tells that the control line of bypass valve C reads too low a voltage, normally because it touches ground somewhere or the coil is shorted. If the engine module switches the valve on the ground side, a grounded wire leaves the valve energised all the time; on an electric recirculation valve, which according to Pierburg works without a vacuum line, that means charge air keeps escaping back to the compressor inlet and boost stays short. If the valve is switched on the supply side, it simply stops opening and the compressor can surge when the throttle snaps shut. No manufacturer publishes P25F9; the Saab circuit check for valve A (10 s, type B) is the nearest documented analogue. The high-voltage counterpart is P25FA.

Symptoms

• Check engine lamp on
• Too little boost if the valve stays open
• Surging or fluttering on lift-off if it stays shut

Most likely causes

• Control wire shorted to ground
• Valve coil shorted internally
• Output stage in the engine control module faulty

What to check, in order

Start with the simplest. You can tick off each step.

1. Check the hoses, clamps, and intercooler
2. With the connector unplugged, check whether the signal wire is making contact with ground.
3. Compare commanded and actual pressure in live data
4. Check the actuator's movement
5. Check the vacuum hoses and the solenoid valve
6. Check the oil and the turbo shaft play before replacing it

Good to know

• Repair difficulty: medium
• It can trigger limp mode.
• It affects emissions.

What each character of P25F9 means

• P: Powertrain: engine and transmission
• 2: Generic code: same on every make
• 5: Speed and idle
• F9: Specific fault in that system

Frequently asked questions

Can I keep driving with code P25F9?

Drive without demanding power and go to a repair shop soon. If you see a lot of blue smoke or hear a metallic noise, shut off the engine.

What causes code P25F9?

The most common causes are: control wire shorted to ground; valve coil shorted internally; output stage in the engine control module faulty.

Related codes

• P25F8Turbocharger/Supercharger Bypass Valve C Control Circuit
• P25FATurbocharger/Supercharger Bypass Valve C Control Circuit High
• P25FBTurbocharger/Supercharger Bypass Valve C Control Circuit Range/Performance
• P0034Turbocharger/Supercharger Bypass Valve A Control Circuit Low
• P00C1Turbocharger/Supercharger Bypass Valve B Control Circuit Low

Sources

• law.cornell.edu: 13 CCR 1968.2
• ms-motorservice.com: electric recirculating air valves
• saabwisonline.com: dtc p0033 p0035

Values and procedures vary by manufacturer. If it affects brakes, steering, fuel or high voltage, see a professional. Updated: 2026-11-04. How we build these pages.