Symptoms of P0256
- 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 P0256
- 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 fuel metering B command, pump feedback, actual fuel pressure, injection timing, RPM, and engine load during the fault.
- Inspect control B wiring, pump connector condition, fuel restriction, air intrusion, fuel quality, and related pressure or timing codes.
- Check whether the issue appears on startup, high load, hot restart, or after injection pump or filter service.
Related OBD-II codes
These nearby fuel / air entries can help compare wording and pin down the fault area.