What it means
The control module detects an electrical fault in the boost pressure sensor B circuit. The code does not by itself identify a boost leak or a wastegate fault.
At a glance
- Usually lights the check-engine light
- Affects emissions; the car can fail an emissions test
How it works
Boost pressure sensor B measures pressure at a second monitored point in the turbocharger or supercharger system, where fitted. P0239 sets when the control module detects an electrical fault in sensor B’s circuit; it does not by itself identify a boost leak or wastegate problem.
Common causes
Most likely first.
- Boost sensor B failure
- Damaged wiring or connector
- Poor electrical connection
- Control module fault
Symptoms
- Check engine light on
- Significant power loss / limp mode
- Possible blue or black smoke from exhaust
- Whistling or hissing sound from intake
How to diagnose it
- Record freeze-frame data and check scan-tool data for boost sensor B and any related pressure sensors to see when the circuit fault occurs.
- Use the vehicle’s service information to identify sensor B, then inspect its connector and wiring for damage, corrosion, moisture, or loose terminals.
- Check sensor B’s power or reference, ground, and signal circuits against the wiring diagram and manufacturer’s specification.
- With the circuit safely isolated, test the sensor B wiring for opens, shorts, or poor continuity, including sections exposed to heat or movement.
- If the wiring is sound, test sensor B and the control module input using the manufacturer’s diagnostic procedure.
Common fixes
- Secure the sensor B connector and repair corroded or damaged terminals.
- Repair an open or short in the boost sensor B wiring.
- Replace boost pressure sensor B if it fails the specified circuit test.
- Repair a control module fault only after sensor B and its circuit have been confirmed good.
Can I keep driving?
If the engine has reduced power or abnormal boost symptoms, avoid hard acceleration and towing until sensor B’s circuit is checked. Stop if severe power loss, heavy smoke, or rough running makes it unsafe to continue.
A code shows where the control module detected a fault, not always which part failed. Check the causes in order and confirm with a test before replacing parts. Have several codes? Check them together
This is a generic code: it means the same on every make. The car’s maker may add more detail in its own service information.