P25F4Turbocharger/Supercharger Boost Sensor C Circuit Low
- Generic OBD-II code · Powertrain
- Turns on the check-engine light
- Matters for the ITP
- Can trigger limp mode
- How the car detects it
- Boost pressure sensors of this kind output a voltage that rises with pressure, so P25F4 – a signal below the lowest valid value – points to the wiring or the sensor rather than to the charge air. Usual reasons are a signal wire shorted to ground, a missing 5 V supply, or an open signal line on an input pulled down by the control unit. No public manufacturer data exist for sensor C; the GM-developed Saab engines give an idea for sensor A, setting the low code under 0.09 V for more than 5 s on the 2.0 litre and under 0.19 V for 4 s in one go or 50 s added up on the 1.6 litre. The control unit then typically disables boost control. The high-voltage counterpart is P25F5; a shared 5 V supply fault can bring up other sensor codes at the same time.
- What you may notice
- Check engine lamp on
- Noticeable loss of power
- Scan tool shows a pressure far below ambient for sensor C
- Likely causes
- LikelySignal wire shorted to ground
- Possible5 V reference open or pulled down by another faulty sensor on the same supply
- PossibleBoost sensor C failed internally
- Inspection (ITP)
- Matters for the ITP. While the check-engine light is on, the car fails the emissions check.
- Repair
- Medium · Often possible to do yourself.Typical cost: €40 – €400
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.