P25FA

Code

Generic P — Powertrain

Turbocharger/Supercharger Bypass Valve C Control Circuit High

Brand: Generic

Type: P — Powertrain

Views: UK: 27 EN: 25 RU: 25

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Page language: EN

Causes

Short to battery on the bypass valve C control wire
Open or corroded ground or connector at solenoid
Failed or internally shorted bypass/diverter valve solenoid (Valve C)
Wiring damage (chafing, pinched, broken conductor)
Poor connector pin contact or corrosion
Blown or incorrect fuse/power feed issue

Symptoms

MIL/Check Engine light illuminated
Reduced or erratic boost control; reduced engine power or limp mode
Turbo surge, hesitation or poor throttle response under boost
Unusual bypass valve noise or constant bypass operation
Possible overboost or underboost depending on stuck state

What to check

Read and record freeze frame and related boost/turbo codes
Visually inspect harness, connectors, and vacuum lines for damage or contamination
Check for corrosion, bent pins, or water ingress at the valve connector
Confirm appropriate fuse(s) and power feed for turbo control circuits
Scan for additional PCM/communication faults that could affect outputs

Signal parameters

Typical control supply (constant) voltage at circuit power feed: ~12 V with key on
Expected solenoid coil resistance (generic): ~10–50 ohms (vehicle-specific)
Control signal type: PCM usually provides PWM/ground-side switching; frequency commonly 20–200 Hz (varies by manufacturer)
Expected control voltage at PCM command line when inactive: near 0 V (ground switching) or oscillating depending on driver type — consult vehicle-specific data

Diagnostic algorithm

Retrieve freeze frame and all stored codes; note engine conditions when fault set.
Inspect valve C connector and harness for damage, corrosion, pin push-out, or water. Repair/clean as needed.
Disconnect the bypass valve C connector. With ignition ON (engine OFF), measure voltage at the power feed terminal of the harness connector — should be ~12 V or vehicle-specified battery voltage.
Measure voltage on the control terminal of the harness with connector disconnected and ignition ON. A steady battery voltage or higher-than-expected voltage indicates a short to battery. A floating/near-0 V may indicate proper state or a PCM ground driver. Compare to vehicle-specific expected behaviour.
Measure resistance of the bypass valve solenoid (at the removed connector) with a multimeter. Compare to manufacturer spec. Very low resistance suggests internal short; infinite/very high suggests open coil.
Check ground continuity from the harness ground pin to chassis ground (0.1 ohm or less preferred). Repair grounds if high resistance.
If wiring and connector appear OK, backprobe the control wire while commanding the valve ON/OFF using a bidirectional scanner or during a boost control test. Observe PWM duty cycle and voltage with a scope or DVM. Look for PWM frequency, duty change with load, and absence of battery-level voltage on the control line.
If harness and solenoid test OK but control line remains high, suspect PCM driver fault. Confirm by substituting a known-good solenoid or installing a fused jumper as temporary test per OEM procedure before replacing PCM.
Clear codes and perform road test under conditions that previously set the fault to verify repair.