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DTC codes / P02xx · Fuel and air metering (injector circuits) / P0240

P0240Turbo/Super Charger Boost Sensor 'B' Circuit Range/Performance

P0240 indicates that the powertrain control module (PCM) has detected an out-of-range or erratic signal from the turbocharger or supercharger boost sensor 'B' circuit, which is often the sensor located after the intercooler or a secondary boost pressure sensor. The PCM compares this signal against expected values from other sensors and sets the code when the voltage or pressure reading falls outside the normal operating window for a calibrated time.

SystemPowertrain
Code typeGeneric (all makes)
SeverityMedium
Fix difficultyIntermediate
AreaFuel and air metering (injector circuits)

Symptoms you may notice

  • Illumination of the check engine light, often with no other noticeable symptoms
  • Reduced engine power or limp mode, especially under acceleration
  • Poor fuel economy or rich-running condition
  • Hesitation, stumble, or surging during acceleration
  • Black smoke from the exhaust on diesel engines
  • Delayed or harsh transmission shifts due to reduced engine torque

Common causes, most likely first

  1. Faulty boost sensor 'B' (internal failure or contamination)
  2. Damaged, chafed, or corroded wiring in the sensor 'B' circuit
  3. Loose or corroded sensor connector pins
  4. Boost leak from a split hose, loose clamp, or cracked intercooler
  5. Restricted or leaking vacuum line to the sensor (if equipped)
  6. Failed or sticking turbocharger wastegate or variable geometry actuator
  7. PCM software issue or internal fault (rare)

How to diagnose and fix it

  1. Perform a visual inspection of the boost sensor 'B', its connector, and associated wiring for damage or corrosion
  2. Check for boost leaks using a smoke machine or pressure test on the intake tract
  3. Measure reference voltage and signal voltage at the sensor connector with a multimeter and compare to manufacturer specifications
  4. Test the sensor's output with a scan tool while manually applying pressure or vacuum to verify linear response
  5. Check vacuum lines and intercooler for restrictions or leaks if the sensor is vacuum-referenced
  6. Inspect the turbocharger wastegate or VGT actuator for proper operation and freedom of movement
  7. Repair or replace faulty wiring, connectors, or the sensor itself, then clear codes and verify the repair with a road test

Boost sensor B faults often misdiagnosed

  • A boost leak after the intercooler can mimic a failed sensor 'B' because the sensor reads lower pressure than expected, so always pressure-test the intake system before replacing parts.
  • On many vehicles, sensor 'B' is the downstream or post-throttle boost sensor, and its signal is used for torque calculations; a skewed reading can cause transmission shift complaints without any boost-related symptoms.
  • Corroded terminals at the sensor connector are a frequent cause that a simple wiggle test may not reveal; back-probing the connector under load is often necessary to catch intermittent voltage drops.
  • The PCM may set P0240 even when the sensor is functional if the turbocharger's wastegate is stuck open, so diagnosing the entire boost control system is essential before condemning the sensor.
  • After repairs, some vehicles require a boost sensor relearn or adaptive reset procedure; failing to perform it can leave the code pending or cause drivability issues.

Can I keep driving with P0240?

You can usually drive the vehicle with P0240, but expect reduced power and possible limp mode under load; avoid heavy acceleration and towing until the fault is repaired to prevent further damage or unsafe driving conditions.

Tools that help

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Guidance is general and written for all OBD-II vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.

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