Symptoms of P0148
- 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 P0148
- 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 commanded fuel pressure, actual pressure, pump command, injector pulse width, fuel trims, engine load, and freeze-frame data.
- Inspect fuel level, filter restriction, pump output, pressure regulator behavior, rail pressure sensor plausibility, and fuel contamination.
- Check whether the fault appears during cranking, acceleration, high load, hot restart, or after fuel system service.
Related OBD-II codes
These nearby fuel / air entries can help compare wording and pin down the fault area.