P25FC: Turbocharger/Supercharger Bypass Valve C - Mechanical

What it means

The third bypass valve is mechanically jammed. Solenoid is energised correctly but the valve flap or disc does not move as expected.

At a glance

• Usually lights the check-engine light

How it works

Bypass valve C is the third valve that redirects air in the turbocharger or supercharger system. This code means the solenoid can be energized but the valve's flap or disc does not move as the control module expects, indicating a mechanical sticking or blockage rather than an identified electrical fault.

Common causes

Most likely first.

1. Carbon buildup blocks the valve flap
2. Actuator linkage seized by corrosion

Symptoms

• Reduced engine power or boost
• Sluggish acceleration
• Check-engine light may illuminate

How to diagnose it

1. Review freeze-frame data and command valve C with a scan tool, if supported, to confirm when the lack of movement occurs.
2. Inspect the valve C housing and accessible air passages for carbon or debris that could obstruct the flap or disc.
3. With the engine off and following the manufacturer's safety procedure, check whether the valve C linkage moves freely.
4. Inspect the actuator linkage and pivot for corrosion, seizure, or damage that could prevent valve travel.
5. If the mechanism moves freely, verify the solenoid command and electrical operation before considering control-module diagnosis.

Common fixes

• Remove carbon or debris from the valve C flap and passage using an appropriate cleaning method.
• Free or replace a corroded or seized valve C linkage.
• Replace bypass valve C if its internal flap or disc remains stuck or damaged.
• Repair a confirmed solenoid or wiring fault if testing reveals an electrical cause.

Can I keep driving?

You may be able to drive gently if the engine runs normally, but avoid high boost, hard acceleration, and towing. Stop if power falls substantially, unusual noises develop, or a temperature warning appears.