Symptoms of P0240
- 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 P0240
- 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 boost sensor B with sensor A, MAP, desired boost, actual boost, airflow, throttle angle, and engine load.
- Inspect boost leaks, sensor port blockage, charge-pipe contamination, connector corrosion, wiring resistance, and sensor response time.
- Check whether the fault occurs only under boost, after heat soak, after intake service, or during deceleration.
Related OBD-II codes
These nearby fuel / air entries can help compare wording and pin down the fault area.