P0240

Turbocharger Boost Sensor B Circuit Range/Performance

P0240 is a generic OBD-II powertrain diagnostic trouble code: Turbocharger Boost Sensor B Circuit Range/Performance. It is logged by the engine control unit when the turbo/boost monitor detects that a specific fault threshold has been exceeded — typically resulting in the malfunction-indicator lamp (MIL / check-engine light) being illuminated.

Code
P0240
Group
Powertrain
System
Turbo/Boost
Severity
Warning (MIL on, possible limp mode)
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What P0240 means

P0240 is a rationality fault: the ECM has detected that Boost Pressure Sensor B is electrically functional (voltage within valid range) but its reading does not agree with the expected boost level derived from other reference sensors — typically the MAP sensor, the barometric pressure sensor (BARO), or Boost Sensor A on twin-turbo platforms. The ECM uses these cross-checks to detect a sensor that is reading plausibly in terms of voltage but inaccurately in terms of actual boost pressure.

On twin-turbocharger vehicles, P0240 often appears when one turbocharger is underperforming relative to the other — for example, a worn turbo on one bank producing less boost while Sensor B reports a lower-than-expected value — causing a cross-comparison failure. On single-turbo platforms, common triggers include a partially blocked sensor port (oil or carbon fouling), a kinked pressure hose reducing the pressure seen at the sensor, or an intercooler boost leak that allows actual pressure to fall below the modelled value.

Because the solenoid and wiring are mechanically intact, the ECM will still attempt to command boost normally but reduce or cap output when the mismatch exceeds the calibrated threshold. This typically activates the MIL and may invoke a mild power reduction strategy rather than full limp mode.

Common causes

Most-frequently reported root causes when P0240 is logged.

  • 1
    Sensor B port clogged with oil mist or carbon deposits, preventing accurate pressure transmission.
  • 2
    Kinked, collapsed, or partially blocked pressure hose between intake pipe and Sensor B.
  • 3
    Intercooler or boost plumbing leak causing actual boost to fall below commanded pressure.
  • 4
    One turbocharger underperforming on a twin-turbo system, creating a cross-sensor mismatch.
  • 5
    Faulty or drifting Boost Pressure Sensor B reading within valid voltage range but physically inaccurate.
  • 6
    Exhaust leak near the turbine inlet affecting turbo spool speed and actual boost output.
  • 7
    Aftermarket tune or boost controller that has altered commanded boost beyond the sensor's calibrated range.

Symptoms drivers notice

Check Engine / MIL light illuminated.
Reduced boost under acceleration — engine feels softer than normal.
ECM may invoke limp-mode boost limiting to prevent sustained pressure mismatch.
On twin-turbo platforms, asymmetric power delivery or hesitation at mid-range RPM.
No visible fault at idle; symptom appears only under moderate to heavy throttle load.
Companion codes P0234 (overboost) or P0299 (underboost) may accompany P0240 if the mismatch is large.

How to diagnose P0240

A typical diagnostic flow when this code is present.

  1. 1
    Scan for all stored codes and note any boost system companions (P0234, P0299, P023x, P024x).
  2. 2
    Perform a visual inspection of all boost hoses and intercooler connections for leaks, cracks, or loose clamps — use a smoke machine if available.
  3. 3
    Inspect the Sensor B pressure port and connecting hose for oil fouling, carbon blockage, or kinking that would reduce the pressure transmitted to the sensor.
  4. 4
    With the engine running, compare Sensor B live data against MAP and Sensor A (if fitted) — the readings should track together under varying throttle; divergence at higher boost confirms a sensor or plumbing fault.
  5. 5
    Test Sensor B voltage sweep from idle to full throttle: approximately 0.5 V at idle rising to 4.5 V at peak boost; a flat or slow-rising curve indicates a clogged port or failing sensor.
  6. 6
    Check wastegate operation — a stuck-open wastegate will cause the boost system to underperform, matching the pattern that triggers P0240.
  7. 7
    Replace Sensor B or repair the pressure hose/port as indicated, clear codes, and verify the fix with a full boost cycle.

Related powertrain codes

Frequently asked questions

How is P0240 different from P0239?

P0239 is a generic circuit malfunction — the voltage is outside the sensor's valid operating range, meaning the circuit itself is faulty. P0240 is a rationality or range/performance fault — the voltage is within a plausible range but the reading does not match what other sensors or models predict, meaning the sensor is electrically alive but physically inaccurate.

Can a dirty sensor cause P0240 without any other symptoms?

Yes. An oil-fouled sensor port may still output a valid voltage at idle where boost is near atmospheric, but under boost the partial blockage prevents full pressure from reaching the sensing element, causing the ECM to see lower boost than commanded and trigger the rationality fault.

On a twin-turbo car, could P0240 indicate one turbo is failing?

Yes. If Turbo B is producing significantly less boost than Turbo A due to worn bearings, a partially seized compressor wheel, or an internal leak, Sensor B will register lower pressure than the ECM expects based on Sensor A's reading and the boost model, triggering the range/performance fault.

Will an aftermarket intercooler cause P0240?

It can, if the intercooler is oversized with significant flow restriction, causing measurable boost pressure drop from the turbo outlet to the sensor. Factory ECM calibrations tolerate a defined pressure differential; exceeding it with a very large aftermarket intercooler without a corresponding tune update may trigger P0240.

Disabling P0240 in software

RaceTune can permanently disable P0240 — and any other OBD-II diagnostic trouble code — on every ECU family we support. The monitor is disabled inside the ECU itself, so the fault stops being logged: the warning light stays off and the engine never enters limp mode for this code. The change is tied to your exact software version.

Permanent
The monitor is disabled in the ECU itself — not just cleared. It cannot return.
Tailored to your file
Each patch is matched to your specific software version — never a one-size-fits-all file.
Reversible
The original file is always preserved. Reflash the stock to return the ECU to factory state.

Software modifications affect emissions compliance and are not road-legal in many jurisdictions. RaceTune service files are intended for motorsport, off-road, and export use.

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