P0240 Turbocharger / Supercharger Boost Sensor "B" Circuit Range / Performance

A turbocharger can be mechanically perfect and still trigger P0240.

That is because this code is not primarily telling you that the turbocharger cannot create boost. It is telling you that the signal coming from Boost Sensor “B” does not behave as the ECM expects.

The distinction is important.

A turbocharger system is controlled through a combination of pressure sensors, actuators, valves, airflow measurements and ECM commands. If one of those signals becomes implausible, the ECM may no longer be able to determine whether the turbocharger is actually doing what it has commanded.

That is essentially the problem behind P0240.

The Important Difference Between “Range/Performance” and “High” or “Low”

P0240 is a range/performance code.

That means the ECM is not necessarily seeing a permanently high or low voltage. Instead, it has detected that the sensor's output does not correspond correctly to the operating conditions or expected pressure.

For example, the sensor might report a pressure that is:

• Too high for the current engine load

• Too low for the current engine load

• Not changing when pressure should change

• Changing too quickly or too slowly

• Inconsistent with another pressure sensor

• Outside the expected relationship between boost, throttle and engine load

This is different from:

P0241 – Boost Sensor “B” Circuit Low

P0242 – Boost Sensor “B” Circuit High

P0240 is therefore less about one specific electrical voltage fault and more about the plausibility and behavior of the sensor signal.

Think of P0240 as a “Does This Reading Make Sense?” Code

One of the easiest ways to understand this fault is to imagine the ECM asking a simple question:

“Given the engine speed, throttle position, load and turbocharger command, does the pressure reported by Sensor B make sense?”

If the answer is repeatedly no, P0240 can be stored.

That means the fault could be inside the sensor circuit, but it could also be somewhere in the actual air/boost system.

This is why P0240 requires a slightly different diagnostic strategy from a straightforward circuit-high or circuit-low fault.

What Is Boost Sensor “B”?

The exact definition of Boost Sensor “B” depends on the vehicle.

It may be a dedicated turbocharger pressure sensor, a charge-air pressure sensor, or another pressure sensor used by the engine management system.

On some engines, pressure sensors are positioned at different points in the intake system. One may measure pressure before the intercooler while another measures pressure closer to the intake manifold.

Other vehicles use a MAP sensor for some or all of these functions.

Therefore, “Sensor B” cannot be assigned to a universal physical location.

The manufacturer's wiring diagram and service information are needed to identify the actual sensor.

Why Does the ECM Need This Sensor?

Turbocharger control is a feedback system.

The ECM doesn't simply tell the turbocharger:

“Produce 1 bar of boost.”

It continuously monitors engine conditions and adjusts the boost-control system according to demand.

The ECM may consider:

• Engine RPM

• Accelerator position

• Engine load

• Airflow

• Intake pressure

• Exhaust conditions

• Engine temperature

• Fuel quantity

• Turbocharger actuator position

• Boost pressure

The pressure sensor provides one of the critical pieces of feedback.

If the sensor reports an implausible value, the ECM can no longer accurately determine the actual pressure inside the intake system.

A Simple Example

Imagine the ECM is commanding increased turbocharger boost during acceleration.

The turbocharger responds normally.

However, Boost Sensor “B” reports almost no pressure increase.

From the ECM's perspective, something is wrong.

It cannot immediately know whether:

• The sensor is defective

• The wiring is faulty

• There is a pressure leak

• The turbocharger isn't responding

• The wastegate is incorrectly positioned

• The actuator has failed

• Another sensor is providing contradictory information

The ECM therefore records a range/performance fault.

This is why P0240 identifies a problem in the relationship between the sensor signal and expected system behavior, not necessarily a failed sensor.

The Most Common Causes

There are several possible causes, and they should not all be treated equally.

Defective boost pressure sensor

The sensor may have become contaminated, internally damaged or electrically unstable.

Damaged sensor wiring

A broken, chafed or partially damaged wire can cause an unstable or implausible signal.

Connector problem

Corrosion, moisture, loose terminals or poor terminal tension can cause intermittent sensor readings.

Blocked or contaminated pressure port

Some pressure sensors have a small pressure passage. Oil residue, carbon or other contamination can interfere with pressure measurement.

Boost leak

A leaking hose, intercooler or connection can prevent the system from producing the pressure expected by the ECM.

Wastegate problem

A wastegate that remains too far open can cause insufficient boost.

A wastegate that fails to open can cause excessive boost.

Turbocharger actuator problem

The actuator may not respond correctly to ECM commands.

Vacuum system problem

On vacuum-controlled turbo systems, a leaking hose, faulty vacuum source or defective control solenoid can prevent proper actuator operation.

MAP/pressure sensor disagreement

If two pressure measurements don't agree as expected, the ECM may identify a range/performance problem.

Turbocharger mechanical fault

Compressor or turbine damage, excessive shaft wear, variable-geometry mechanism problems or other mechanical faults can affect boost response.

ECM problem

Possible, but generally much less common than problems with the sensor, wiring, air system or boost-control hardware.

What P0240 Does Not Tell You

P0240 does not tell you exactly which component has failed.

It does not prove that:

• The turbocharger is broken

• The boost sensor is defective

• The wastegate is stuck

• The intercooler is leaking

• The actuator has failed

The code is essentially a starting point for diagnosis.

This is particularly important because turbochargers can be expensive.

Replacing one simply because P0240 appears can turn a relatively inexpensive sensor or hose problem into a very expensive repair.

The Best Place to Start: Live Data

With a range/performance code, live data can be more informative than simply measuring resistance.

A scan tool can often display parameters such as:

• Boost pressure

• MAP pressure

• Desired boost

• Actual boost

• Engine load

• MAF airflow

• Wastegate command

• Turbo actuator position

• Throttle position

The exact parameters available depend on the vehicle.

The objective is to determine whether the reported pressure changes logically as engine conditions change.

Check the Reading With the Engine Off

An extremely useful basic check is to look at the pressure reading with the engine off.

At this point, there should normally be no significant intake vacuum or turbocharger-generated boost.

The pressure sensor should therefore report a value reasonably consistent with atmospheric pressure, depending on sensor type and altitude.

If Sensor B reports something obviously unrealistic before the engine even starts, the investigation should immediately focus on:

• Sensor

• Wiring

• Reference voltage

• Ground

• Signal circuit

• Sensor calibration

rather than immediately blaming the turbocharger.

Watch What Happens During Acceleration

The next question is how the sensor behaves when the engine is running.

As engine load and turbocharger activity increase, the pressure reading should respond appropriately.

A sensor that remains frozen at one value is suspicious.

A sensor that suddenly jumps to an impossible value is suspicious.

A sensor that responds much differently from the expected boost behavior is also suspicious.

This is where P0240 becomes a data-analysis problem, rather than simply a parts-replacement problem.

Compare Desired Boost With Actual Boost

If the vehicle provides both values, this is one of the strongest diagnostic tools available.

Suppose the ECM requests increased boost but actual pressure remains low.

Possible causes include:

• Boost leak

• Wastegate stuck open

• Actuator problem

• Vacuum problem

• Turbocharger mechanical fault

• Incorrect sensor reading

Now consider the opposite.

The ECM requests moderate boost but actual pressure becomes excessively high.

Possible causes include:

• Wastegate not opening

• Sticking VGT mechanism

• Actuator problem

• Boost-control solenoid problem

• Incorrect pressure feedback

• Turbocharger control problem

The important thing is that P0240 should be diagnosed according to the actual pattern of the data.

Inspect the Charge-Air System

A boost pressure sensor can report a perfectly accurate low pressure if the intake system has a leak.

Inspect:

• Turbocharger outlet hose

• Intercooler

• Intercooler connections

• Intake pipes

• Hose clamps

• Plastic charge pipes

• Rubber couplers

• Intake manifold connections

Look for oil traces around connections as well.

A small amount of oil mist can accumulate around a pressurized intake leak and provide a useful visual clue.

A proper pressure or smoke test may be necessary when a leak is suspected.

Inspect the Wastegate

The wastegate controls how much exhaust energy reaches the turbocharger turbine.

If it does not move correctly, boost pressure can become inconsistent with the ECM's expectations.

Check for:

• Sticking linkage

• Corrosion

• Excessive play

• Bent linkage

• Damaged actuator rod

• Incorrect actuator movement

Do not assume that a functioning electrical solenoid means the wastegate itself is mechanically healthy.

What About Variable Geometry Turbochargers?

Not every turbocharged engine uses a conventional wastegate.

Diesel engines and some gasoline engines use variable geometry turbochargers (VGT/VNT).

Instead of simply opening a wastegate, the turbocharger changes vane position to regulate turbine behavior.

In such systems, the equivalent boost-control problem may involve:

• Vane position

• Electronic actuator

• Vacuum actuator

• Position feedback

• Vacuum supply

• Carbon-related vane sticking

Therefore, the generic description of P0240 should always be interpreted according to the actual turbocharger architecture.

Electrical Testing Still Matters

Although P0240 is a range/performance code, the sensor circuit should still be electrically tested.

Depending on the system, check:

5-volt reference

The sensor may require a stable reference voltage from the ECM.

Ground

A poor sensor ground can distort the signal.

Signal

The signal should change appropriately with pressure.

Wiring

Check for opens, shorts and excessive resistance.

Connector

Check terminal condition and contact quality.

Continuity alone is not enough.

A damaged wire may pass a basic continuity test but develop excessive resistance when the circuit is operating or when the harness moves.

A Sensor Can Be Electrically Good and Still Be Wrong

This is another important diagnostic point.

A pressure sensor can have:

• Correct supply voltage

• Correct ground

• Apparently normal wiring

• No obvious connector damage

and still produce an incorrect pressure reading.

This can happen because the sensor's internal pressure-sensing element or calibration has failed.

Therefore, electrical testing should be combined with pressure plausibility testing.

What If P0240 Appears Together With Other Codes?

Additional codes can completely change the diagnostic direction.

For example, P0240 combined with a boost-control actuator code points toward a different investigation than P0240 alone.

Likewise, if there are several sensor reference-voltage codes, investigate the shared 5-volt reference before replacing the boost sensor.

If there are MAF, MAP and turbocharger codes together, compare the sensors and system data rather than treating every code as a separate component failure.

The first code is not always the root cause.

Can a Dirty Air Filter Cause P0240?

A severely restricted air filter can influence airflow and turbocharger operation, but it is not normally the first explanation for a dedicated boost sensor range/performance code.

It should still be inspected during a broader turbocharger diagnosis, especially when airflow-related data is abnormal.

But replacing the air filter without confirming a restriction is not a diagnosis.

Can a Boost Leak Cause P0240?

Yes.

A significant boost leak can cause actual pressure to remain outside the expected range.

For example, the ECM commands increased boost, but air escapes through a damaged intercooler hose.

The pressure sensor reports less boost than expected.

The ECM sees a mismatch and may eventually store P0240.

This is one reason a range/performance code should not be treated as purely electrical.

Can a Bad Boost Sensor Cause P0240?

Absolutely.

In fact, the sensor itself is one of the first components that should be investigated.

But the correct approach is to prove the sensor is reporting incorrectly rather than replacing it simply because its name appears in the code.

Can P0240 Cause Limp Mode?

Yes.

If the ECM cannot trust boost pressure information, it may reduce engine output.

The vehicle can enter limp mode to prevent:

• Excessive boost

• Incorrect fueling

• Engine damage

• Turbocharger damage

• Excessive emissions

The driver may experience a dramatic reduction in power.

After the ignition is switched off and restarted, the vehicle may temporarily feel normal again if the fault is intermittent or the ECM returns to a default control strategy.

Intermittent P0240

An intermittent fault deserves special attention to wiring and temperature.

The problem may appear only when:

• The engine is hot

• Turbocharger temperature is high

• Engine movement increases

• Harness vibration occurs

• Boost pressure rises

• A connector expands with heat

• A damaged wire moves

In these cases, the vehicle can behave perfectly during a short workshop inspection.

Monitoring live data while reproducing the fault can be much more useful than simply clearing the code.

A Practical Diagnostic Scenario

Imagine a vehicle that drives normally at light throttle.

During hard acceleration, the driver feels a sudden loss of power and P0240 appears.

The first assumption might be:

“The turbocharger has failed.”

But the diagnostic process shows:

• Turbocharger actuator moves correctly

• Wastegate mechanism is free

• No boost leak is found

• Desired boost is reasonable

• Sensor B suddenly reports an implausible pressure value

The turbocharger may therefore be perfectly healthy.

The actual fault could be the sensor or its electrical circuit.

Now consider another vehicle with the same P0240.

This time:

• Sensor readings are electrically plausible

• Desired boost increases

• Actual boost remains far below target

• Pressure testing finds a leaking intercooler hose

The same diagnostic code has a completely different root cause.

That is why the code should guide the diagnosis, not dictate the replacement part.

When Should the Turbocharger Be Suspected?

The turbocharger becomes a stronger suspect when the supporting evidence points in that direction.

For example:

• Boost remains incorrect after control-system testing

• Actuator operation is correct

• Wiring and sensors test correctly

• No charge-air leak is present

• Wastegate/VGT mechanism operates correctly

• Actual boost consistently fails to follow command

• Mechanical inspection reveals abnormal turbocharger condition

Only then does turbocharger replacement or rebuilding become a logical conclusion.

Recommended Diagnostic Order

For P0240, a sensible diagnostic sequence is:

Scan all DTCs

↓

Check freeze-frame and live data

↓

Identify the exact Boost Sensor “B”

↓

Check sensor reading with engine off

↓

Inspect connector and wiring

↓

Verify reference voltage and ground

↓

Check sensor signal

↓

Compare sensor data with actual pressure

↓

Compare desired boost with actual boost

↓

Inspect charge-air hoses and intercooler

↓

Test wastegate/VGT actuator and mechanism

↓

Check vacuum/pressure control system where applicable

↓

Evaluate turbocharger mechanically

↓

Consider ECM fault only after the external system has been verified

This sequence helps prevent unnecessary parts replacement.

P0240 vs P0241 vs P0242

These three codes belong to the same Boost Sensor “B” group but point in different directions.

P0240 indicates a range/performance problem. The sensor signal does not behave as expected for the operating conditions.

P0241 indicates a low circuit signal.

P0242 indicates a high circuit signal.

This distinction matters diagnostically.

With P0241 or P0242, electrical circuit testing becomes especially important.

With P0240, you need to look at both electrical signal integrity and actual boost-system behavior.

Final Diagnosis

P0240 – Turbocharger/Supercharger Boost Sensor “B” Circuit Range/Performance means the ECM has determined that the pressure information from Boost Sensor “B” is outside the expected operating range or does not correspond correctly to the engine's operating conditions.

The sensor may be faulty, but it is only one possibility.

The actual cause can also be:

• Wiring or connector problems

• Incorrect sensor reference or ground

• Boost leak

• Wastegate malfunction

• VGT/VNT actuator problem

• Vacuum or pressure-control problem

• MAP/boost sensor disagreement

• Turbocharger mechanical fault

• ECM-related problem

The most effective diagnosis is therefore not “replace Boost Sensor B.”

It is:

“Find out why the pressure reported by Sensor B does not agree with what the engine control system expects.”

Once the sensor signal, actual pressure, commanded boost and mechanical boost-control system are compared, P0240 becomes much easier to isolate—and an expensive turbocharger replacement can often be avoided.