P25F4 code meaning
Turbocharger/Supercharger Boost Sensor C Circuit Low
Powertrain system Generic code P25xx codes Check engine light
What P25F4 means
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.
P25F4 at a glance
- Check engine lightYes, usually on
- Emissions testCan fail
- Limp modePossible
- Repair difficultyMedium, DIY possible
- Typical labor0.5 to 2 hours
- Clears after repairWhen cleared with a scanner
Symptoms of P25F4
- Check engine lamp on
- Noticeable loss of power
- Scan tool shows a pressure far below ambient for sensor C
Common causes of P25F4
- Most 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
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
Boost pressure sensor cWiring harness
What each part of P25F4 means
| P | Powertrain system: engine, fuel system, ignition, emissions and transmission. |
| 2 | Generic code (second SAE range): it means the same on every make. |
| 5 | Area: vehicle speed, idle control and auxiliary inputs. |
| F4 | The exact fault in that area. |
What to do next
- Note P25F4 and any other codes stored with it: several codes together often point to one cause.
- Check for loose connectors and damaged wiring around the parts the code names.
- Check open recalls for your car: some faults are fixed for free by the dealer. Enter your VIN.
- Clear the code only after the repair. If it comes back, the fault is still there.
Buying a used car? Scan it for stored codes before you pay. A recently cleared memory can hide a problem.
Questions about P25F4
What does P25F4 mean?
P25F4 means "Turbocharger/Supercharger Boost Sensor C Circuit Low". 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. It is a generic code, so it means the same on every make.
Is it safe to drive with P25F4?
Drive gently and only to a workshop. With P25F4 the car can go into limp mode (reduced power) to protect itself.
Will P25F4 fail an emissions test?
Yes, it can. P25F4 is emissions-related, so most inspection programs fail a car while it is stored or while the check engine light is on.
How hard is P25F4 to fix?
Difficulty: medium. A typical repair takes 0.5 to 2 hours of work. A careful DIY repair is possible with basic tools and a scanner.
Will P25F4 clear itself after the repair?
Clear the code with a scanner after the repair. If the fault is fixed, it does not come back.