P0239 Turbocharger/Supercharger Boost Sensor B Circuit Malfunction

P0239 indicates a turbocharger or supercharger boost sensor B circuit malfunction. The second boost pressure input is not reliable.

Code details

Generic OBD-II · P0

System: Fuel / Air
Code type: Generic (SAE / ISO controlled)
Standard: SAE J2012 / ISO 15031-6

Diagnostic boundary

A diagnostic trouble code reports that a monitored test failed. It does not prove one specific part is bad, and manufacturer logic can add vehicle-specific conditions.

Do not replace boost-control hardware before verifying boost sensor B circuit and pressure plausibility.

Symptoms of P0239

Check-engine light on, sometimes with rough or uneven running.
Hesitation, surging, or a noticeable change in fuel economy.
Occasionally hard starting or a smell of unburnt fuel.

Common causes of P0239

A failing or contaminated sensor (MAF, MAP, oxygen or air-fuel sensor).
Intake or vacuum leaks, or an exhaust leak near an upstream sensor.
Wiring, connector, or fuel-delivery problems that skew the reading.

Useful checks before replacing parts

Compare boost sensor B with sensor A, MAP, BARO, desired boost, throttle angle, airflow, and key-on pressure readings.
Check sensor B signal, reference voltage, ground, connector fit, charge-pipe routing, sensor port contamination, and wiring continuity.
Inspect boost leaks, intake plumbing, intercooler service areas, and related boost control or correlation codes.

Related OBD-II codes

These nearby fuel / air entries can help compare wording and pin down the fault area.