Faulty boost pressure sensor 'B' (often the downstream or post-throttle sensor); Damaged or corroded wiring harness or connector at the sensor; Intake air leaks or boost leaks between the turbocharger and intake manifold; Clogged or restricted intercooler or charge air cooler; Failed or dirty mass airflow sensor affecting boost calculations; Sticking or faulty turbocharger wastegate or variable geometry actuator; Engine control module software issues or internal faults (less common)

DTC codes / P02xx · Fuel and air metering (injector circuits) / P0239

P0239Turbo/Super Charger Boost Sensor 'B' Circuit

Q: What does code P0239 mean?

Turbo/Super Charger Boost Sensor 'B' Circuit. P0239 indicates that the powertrain control module has detected an out-of-range signal on the 'B' circuit of the turbocharger or supercharger boost sensor, which is often the sensor that monitors pressure after the throttle body or intercooler. The computer compares this signal against expected values and sets the code when the voltage or rationality check fails.

P0239 indicates that the powertrain control module has detected an out-of-range signal on the 'B' circuit of the turbocharger or supercharger boost sensor, which is often the sensor that monitors pressure after the throttle body or intercooler. The computer compares this signal against expected values and sets the code when the voltage or rationality check fails.

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 under acceleration
Poor fuel economy or sluggish throttle response
Rough idle or hesitation during light acceleration
In rare cases, a noticeable loss of boost pressure

Common causes, most likely first

Faulty boost pressure sensor 'B' (often the downstream or post-throttle sensor)
Damaged or corroded wiring harness or connector at the sensor
Intake air leaks or boost leaks between the turbocharger and intake manifold
Clogged or restricted intercooler or charge air cooler
Failed or dirty mass airflow sensor affecting boost calculations
Sticking or faulty turbocharger wastegate or variable geometry actuator
Engine control module software issues or internal faults (less common)

How to diagnose and fix it

Perform a visual inspection of the boost sensor 'B' and its wiring for damage, corrosion, or loose connections
Use a scan tool to check live data for boost pressure sensor 'B' and compare with sensor 'A' and manifold absolute pressure readings
Check for intake and boost leaks using a smoke machine or pressure test
Test the sensor 'B' reference voltage and signal voltage with a multimeter, following manufacturer specifications
Inspect the intercooler and charge pipes for restrictions or blockages
Replace the boost pressure sensor 'B' if testing confirms it is faulty
Clear the code and perform a road test to verify the repair and ensure the code does not return

Boost sensor B misdiagnosis traps

Many technicians replace the boost sensor 'B' without first checking for intake leaks, which can mimic a sensor fault by causing unexpected pressure readings.
The 'B' circuit often refers to a sensor located after the throttle body, so a sticking throttle body or carbon buildup can skew its readings and set this code.
A dirty or failing mass airflow sensor can cause the computer to calculate incorrect boost pressure, leading to a P0239 without any fault in the boost sensor itself.
On some vehicles, the boost sensor 'B' shares a reference voltage with other sensors, so a short in a related circuit can trigger this code along with others.
Intermittent wiring faults at the sensor connector are common and may not appear during static testing, so a wiggle test while monitoring live data is essential.

Can I keep driving with P0239?

You can generally drive with this code, but avoid heavy acceleration and towing until it is diagnosed, as the engine may enter limp mode and boost performance can be reduced.

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.