What it means
The boost pressure sensor B reading is outside the expected range or does not respond as expected under the monitored conditions.
At a glance
- Usually lights the check-engine light
- Affects emissions; the car can fail an emissions test
How it works
Boost pressure sensor B reports pressure in the turbocharger or supercharger air path to the control module. P0240 sets when its reading is outside the expected range or fails to respond as expected as operating conditions change.
Common causes
Most likely first.
- Sensor reading drifted
- Sensor element aged beyond calibration window
- Sensor mounting loose - signal damping
Symptoms
- Check engine light on
- Significant power loss / limp mode
- Possible blue or black smoke from exhaust
- Whistling or hissing sound from intake
How to diagnose it
- Review freeze-frame data and graph boost sensor B live data as engine load changes to see when its response becomes implausible.
- With the engine off, compare the sensor reading with the other available pressure readings under the same conditions.
- Inspect boost sensor B and its mounting for looseness, damage, contamination, or a poor seal that could distort the reading.
- Check the sensor connector and wiring for corrosion, damage, loose terminals, or intermittent contact.
- Test boost sensor B and its circuit against the manufacturer's specifications before replacing the sensor.
Common fixes
- Secure a loose boost sensor B mounting and restore its proper seal.
- Clean or reconnect the sensor connector and correct poor terminal contact.
- Repair damaged wiring in the boost sensor B circuit.
- Replace boost sensor B if testing confirms that its output is inaccurate or unresponsive.
Can I keep driving?
If the vehicle has reduced power or limp mode, avoid hard acceleration and high boost, and drive only as needed for diagnosis. Stop if power loss makes the vehicle unsafe or heavy smoke appears.
A code shows where the control module detected a fault, not always which part failed. Check the causes in order and confirm with a test before replacing parts. Have several codes? Check them together
This is a generic code: it means the same on every make. The car’s maker may add more detail in its own service information.