P0240 Code: Boost Sensor B Circuit Range/Performance
P0240: Compare the Pressure Channels
Separate sensor plausibility from actual underboost, overboost and airflow faults.
DIAGNOSTIC FOCUS
- FAULT TYPE
- Boost sensor B plausibility
- FIRST CHECKS
- Key-on comparison, response, wiring and pressure path
Sensor B location and whether it measures pre-throttle, manifold, charge pipe or another stage are vehicle specific.
P0240 means Turbocharger/Supercharger Boost Sensor B Circuit Range/Performance. The controller judged boost sensor B's value or response implausible compared with expected pressure, another sensor or operating conditions. The code does not prove the turbocharger is bad, and it differs from P0241 low or P0242 high electrical limit faults.
Save the complete fault event before clearing it: boost sensor A/B, MAP, barometric and throttle/airflow data, commanded boost or wastegate position, engine speed/load, temperatures and companion underboost/overboost codes. Map sensor B, compare all pressure sensors key-on engine-off, inspect its hose/port and circuit, then evaluate response under a safe controlled load before testing turbo hardware.
What Does the P0240 Code Mean?
Boosted engines may use several pressure sensors before and after the compressor, charge-air cooler or throttle. The controller can compare them with barometric pressure at key-on and with modeled airflow and boost during operation.
Range/performance means the signal can remain inside its electrical rails yet disagree with physics or another channel. That is different from a circuit-low/open or circuit-high short code.
A contaminated sensor, blocked pressure port, hose leak, wiring bias, wrong part or genuine boost-control fault can all create implausibility. The correlation pattern decides whether to remain in the sensor path or move to air/boost hardware.
With the engine off and pressure stabilized, compare sensor B with MAP, barometric and sensor A as the OEM directs.
Graph pressure channels during a controlled load change. A biased, slow or flat response differs from real system-wide boost loss.
Inspect sensor port, hose, charge-air plumbing and condensate/contamination before condemning electronics.
P0240 Symptoms, Severity, and Driving Safety
The plausibility monitor can find a small offset before the driver notices performance.
The controller may limit torque when pressure information is unreliable. Save command and actual data.
A false pressure signal or actual boost leak can affect control, but fuel and ignition faults remain separate.
Wrong part, damaged seal, blocked port or connector trouble can create an immediate correlation error.
P0299 or P0234 changes the test path toward physical boost control only after the sensor signals are proven.
Condensation, oil contamination or temperature-sensitive wiring can alter a pressure port or signal.
A stable MIL may allow cautious travel, but reduced power, abnormal turbo noise, smoke, oil leakage, detonation, severe surging or an overboost warning requires stopping. Avoid full-load tests until sensor plausibility is established.
P0240 Causes: Biased Sensor, Circuit, Pressure Port, or Boost System?
Start with static pressure correlation, then follow sensor B's physical port and electrical path. Test actual boost hardware only after the pressure channels are trustworthy.
Biased or Contaminated Sensor B
Oil mist, water or internal drift can keep the signal in range but incorrect.
How to prove it: Compare stabilized pressure and response with peer sensors before cleaning or replacement.
Check firstBlocked, Split, or Misrouted Pressure Port/Hose
Restriction or leakage can delay or distort only sensor B's pressure exposure.
How to prove it: Inspect the exact port and hose, then apply only approved low-pressure testing.
Check firstReference, Ground, or Signal Resistance
A shared reference or ground drop can bias the signal without a hard low/high code.
How to prove it: Compare companion sensors and voltage-drop the circuit at the sensor under operating conditions.
Verify directlyWrong Sensor, Seal, or Calibration
An incorrect transfer function or installation leak can fail correlation after recent service.
How to prove it: Verify part number, connector, seal and calibration applicability by VIN.
Verify directlyCharge-Air Leak or Restriction
A hose, cooler or throttle-path problem can make pressure channels disagree depending on their locations.
How to prove it: Smoke/pressure-test the charge path within OEM limits after sensors and ports are proven.
Verify directlyBoost-Control or Turbo Mechanical Fault
Wastegate, actuator, bypass valve or turbo damage can create real pressure behavior outside the model.
How to prove it: Compare command/position and physical boost evidence; do not infer turbo failure from P0240 alone.
Final branchDo not reuse one cross-sensor pressure threshold. OEM publications show different sensor locations and calibrated comparison windows. Use the exact pressure units and test condition.
Using UR800 to Organize P0240 Evidence
The iCARZONE UR800 Full-System Bidirectional Scan Tool with ECU Coding supports full-system diagnostics, available DTCs, freeze frame, ECU information and live data. Graph boost sensor B, sensor A, MAP, barometric pressure, commanded boost, wastegate/bypass command or position, airflow, throttle, speed/load and temperatures. Key-on comparison and same-time overlay are more useful than one snapshot.
The official product page advertises bidirectional control and ECU coding. Coverage varies by VIN, ECU and software. A scan value cannot prove actual gauge pressure, port blockage, hose integrity, sensor transfer function or turbo mechanical condition. Active boost-control tests are VIN- and condition-dependent.
Use a calibrated pressure source/gauge only within the published range, a high-impedance meter and an approved charge-system smoke/pressure test. Avoid heat, rotating parts and uncontrolled boost.
iCARZONE UR800 Full-System Bidirectional Scan Tool with ECU Coding
Overlay boost sensor B with MAP, barometric and supported boost-control data before replacing the sensor or turbo.
Price and availability checked September 2, 2026. Prices shown are USD. Recheck the current offer, stock and required vehicle/function coverage before purchase.
How to Diagnose P0240 With Pressure Correlation Data
P0240 is a comparison problem. Establish the correct sensor-B location and compare stabilized and dynamic pressure channels before deciding whether the fault is electrical, pneumatic or true boost control.
P0240 Quick Diagnostic Path
-
1
Capture Pressure and Boost Context
- Save P0240 status, freeze frame and all airflow, pressure, boost-control, fuel and ignition faults.
- Record sensor A/B, MAP, BARO, command/position, airflow, throttle, speed/load and temperature at the event.
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2
Identify Sensor B and Its Pressure Source
- Use VIN diagrams to locate sensor B and determine what side of the compressor, cooler or throttle it measures.
- Verify connector, part application, port, hose and any integrated temperature element.
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3
Perform a Stabilized Key-On Comparison
- At the OEM-specified key-on engine-off condition, compare B with MAP, BARO and other pressure channels.
- Use correct units and altitude context; do not impose one universal allowed difference.
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4
Inspect and Test the Sensor Path
- Check contamination, restriction, hose damage, seals, reference, ground and signal voltage/drop.
- Apply a calibrated pressure only within the published range and watch for smooth response.
-
5
Evaluate Dynamic Correlation and Boost Hardware
- Graph all pressure channels during a safe controlled load change after static checks pass.
- If the whole system response is abnormal, test charge leaks, restriction, wastegate/bypass and turbo condition without uncontrolled boost.
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6
Repair and Verify the Pressure Model
- Repair the proven sensor/port/circuit, charge-air leak/restriction, actuator or mechanical issue.
- Repeat stabilized comparison and controlled-load graph, confirm expected command/response and no returning P0240 or under/overboost faults.
How to Fix P0240 and Verify the Repair
Clean or Repair the Sensor-B Pressure Path
Correct a proven blocked port, damaged hose, seal or contamination source.
Repair the Sensor-B Circuit or Replace a Proven Sensor
Restore reference/ground/signal integrity or use a verified VIN-correct sensor.
Seal a Proven Charge-Air Leak or Restriction
Repair hoses, cooler or joints only when pressure-location evidence identifies the physical path.
Service a Proven Boost-Control or Turbo Fault
Use command/position and mechanical evidence before actuator or turbo replacement.
Pressure-Channel Data Diagnosis
VIN-specific quoteMapping, stabilized comparison and dynamic overlay establish scope.
Sensor/Port or Harness Service
VIN-specific quoteAccess, contamination and sealed-wire repair affect labor.
Charge-Air Leak/Restriction Repair
VIN-specific quoteSmoke/pressure testing and cooler/hose access determine cost.
Actuator or Turbo Work
VIN-specific quoteMechanical verification, oil/coolant lines and calibration make this a separate estimate.
Ask the estimate to separate sensor/circuit, pressure-port, charge-air plumbing and turbo-control work. P0240 alone cannot justify a turbocharger.
Verification needs both a stabilized pressure correlation and correct dynamic response under safe load. A new sensor with an unchanged biased comparison is not a pass.
P0240 Sensor Locations, Boost Safety, and DIY Limits
An Audi Q5/SQ5 quick-reference book defines P0240 and shows multiple cross-checks among boost, inlet and ambient sensors for listed applications.
B may read a different charge-air stage; identify its actual pressure source.
Range/performance can be a correlation failure even when voltage is inside normal rails.
P0241 and P0242 target electrical extremes; do not merge them with P0240.
Those pressure differences and thresholds are specific to the documented engines. Another architecture may locate sensor B elsewhere or compare a different set of channels.
- Save pressure channels and load conditions.
- Inspect accessible ports, hoses and connectors.
- Compare key-on readings in consistent units.
- Stop for smoke, oil leak or severe turbo noise.
- Apply pressure without the OEM limit.
- Run uncontrolled road-load boost tests.
- Probe hot/rotating turbo areas.
- Condemn actuators or turbo internals without proof.
Frequently Asked Questions About P0240
What does P0240 mean?
Is the turbocharger bad?
Where is boost sensor B?
How is P0240 different from P0241/P0242?
Can I clean the sensor?
Can the vehicle be driven?
Can UR800 diagnose P0240?
How is the repair verified?
Sources and Technical Review Notes
- Audi Q5/SQ5 Quick Reference Specification Book — Defines P0240 and documents application-specific cross-sensor range/performance checks.
- VW Touareg Quick Reference Specification Book — Provides related charge-pressure sensor and pump circuit context with application-specific criteria.
- Ford 2024–2025 Gasoline OBD System Summary — Explains pressure-sensor correlation, boost-control and airflow monitor concepts on a different OEM architecture.
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