P0240
Turbocharger/Supercharger Boost Sensor B Circuit Range/Performance
Encountering the engine check light code P0240 signifies an explicit mechanical or electrical operational breakdown categorized as "Turbocharger/Supercharger Boost Sensor B Circuit Range/Performance". Professional scanner tools usually flag this subsystem loop early on.
Driver's Summary
When your OBD2 scanner shows P0240, the engine control module has flagged an issue specifically related to turbocharger/supercharger boost sensor b circuit range/performance. You may notice poor acceleration, check engine light, failure to build boost, all of which are direct consequences of this malfunction. Short trips are generally acceptable, but avoid high-load driving and get this inspected soon.
Symptoms
Poor acceleration, check engine light, failure to build boost
Common Causes
- Defective Boost Sensor B
- Vacuum line leak to the sensor
- Corroded electrical connection
- Internal turbocharger failure
How to Fix
- 1 Replace Boost Sensor B
- 2 Replace degraded vacuum lines
- 3 Clean and grease sensor connector
- 4 Inspect turbocharger fins and bearings
Technical Explanation
To set P0240, the PCM samples the affected circuit multiple times per second, comparing live readings against manufacturer-programmed operating windows. Misfire rate is counted per cylinder over rolling windows and compared against two thresholds: a catalyst-damaging rate (triggers flashing MIL) and an emissions-exceeding rate (triggers solid MIL). The PCM logs which cylinder is misfiring based on crankshaft position at the time of each detected event. Once confirmed, the code is stored as a permanent DTC and the MIL is activated. The freeze frame snapshot — recording RPM, load, coolant temperature, and fuel trim at fault detection — is also saved and is critical for accurate diagnosis.
Is It Safe to Drive?
You can drive short distances, but the symptoms — poor acceleration, check engine light, failure to build boost — indicate the affected system is compromised. Leaving this unresolved will lead to progressively worse fuel economy and potential damage to components beyond the original fault.
Mechanic's Pro Tip
For P0240, always perform a smoke test before replacing any parts — unmetered air from a cracked intake boot, split hose, or failed gasket is the root cause in the majority of lean fault cases and costs almost nothing to fix. After any repair, clear the code and watch short-term fuel trim (STFT) live on a scan tool; it should recover to within ±5% at idle within 2–3 minutes if the vacuum leak is truly resolved.
Sensor: $100 - $200; Turbocharger replacement: $1,000 - $1,500+