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Home / DTC / P25FA — Turbocharger/Supercharger Bypass Valve C Control Circuit High

P25FA — Turbocharger/Supercharger Bypass Valve C Control Circuit High

Detailed page for trouble code P25FA.

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Code

P25FA

Generic P — Powertrain

Turbocharger/Supercharger Bypass Valve C Control Circuit High

Brand: Generic
Type: P — Powertrain
Views: UK: 17 EN: 15 RU: 13
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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

  1. Retrieve freeze frame and all stored codes; note engine conditions when fault set.
  2. Inspect valve C connector and harness for damage, corrosion, pin push-out, or water. Repair/clean as needed.
  3. 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.
  4. 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.
  5. 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.
  6. Check ground continuity from the harness ground pin to chassis ground (0.1 ohm or less preferred). Repair grounds if high resistance.
  7. 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.
  8. 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.
  9. Clear codes and perform road test under conditions that previously set the fault to verify repair.

Likely causes

  • Short to constant 12V on the solenoid control wire
  • Failed solenoid with low internal resistance or internal short
  • Corroded/poor connector pin causing intermittent high-voltage reading
  • Open ground at solenoid or poor chassis ground connection

Fault status

⚠️ Status
Turbocharger/Supercharger Bypass Valve C Control Circuit High
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 0.5-2.0 hours

Similar codes

P25F9 P25FB P0243 P0234 P0299
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