Symptoms of P0257
- Check-engine light on, sometimes with rough or uneven running.
- Hesitation, surging, or a noticeable change in fuel economy.
- Occasionally hard starting or a smell of unburnt fuel.
Common causes of P0257
- A failing or contaminated sensor (MAF, MAP, oxygen or air-fuel sensor).
- Intake or vacuum leaks, or an exhaust leak near an upstream sensor.
- Wiring, connector, or fuel-delivery problems that skew the reading.
Useful checks before replacing parts
- Compare metering B command, actual pressure, pump feedback, fuel temperature, injection timing, and engine load over the fault drive cycle.
- Inspect fuel restriction, actuator response, connector voltage drop, fuel contamination, air in fuel, and pump calibration status.
- Check whether the performance error appears during cranking, acceleration, high load, hot operation, or rapid fuel demand changes.
Related OBD-II codes
These nearby fuel / air entries can help compare wording and pin down the fault area.