Turbocharger Boost Sensor B Malfunction
The engine's turbo boost pressure sensor B is sending an invalid signal or out-of-range reading to the computer. Think of it like a faulty tire pressure gauge that gives wildly incorrect readings.
The ECU monitors voltage output from the boost sensor B to determine actual manifold pressure for turbo control and fuel injection timing. The sensor should produce a voltage proportional to boost pressure (typically 0.5-4.5V). If the signal is stuck, erratic, or outside expected range, the ECU cannot properly regulate boost and fuel delivery.
| Parameter | Normal Range | Fault Condition |
|---|---|---|
| Sensor Voltage Output | 0.5V to 4.5V (proportional to boost pressure) | Below 0.5V, above 4.5V, or no signal change |
| Boost Pressure Logic | Sensor voltage matches expected boost under load | Voltage does not correlate with engine load or remains static |
Code P0240 is a moderate fault. You can generally drive to a workshop, but avoid long trips or high-load driving (motorway, uphill towing) until it is diagnosed. If the code keeps returning after clearing, or if you notice the symptoms listed above worsening, do not delay professional diagnosis. Many moderate codes have multiple possible root causes — a mechanic with live OBD data can identify the exact fault more efficiently than part-by-part trial and error.
Once the fault is repaired, P0240 can be cleared using any OBD-II scanner. Connect the scanner, navigate to "Clear Codes" or "Erase DTCs," and confirm. The check engine light turns off immediately.
The code will return if the root cause was not actually fixed. The ECM re-detects the fault within 1–3 drive cycles and sets the code again.