What does it mean?
Here the B turbocharger outlet pressure sensor circuit is electrically sound, but the value it reports does not agree with what the engine should be producing. The module builds an expected compressor outlet pressure from engine speed, load, commanded wastegate or vane position, barometric pressure and the manifold pressure sensor, then compares that model with the measured signal. When the difference stays outside the allowed window for a set time, the reading is judged implausible. A classic example is a sensor that reads correctly at key-on but never rises as boost builds, or one that reports pressure while the engine is off. Because a wrong boost value can lead to real overboost or underboost, the module usually limits boost and reduces power while the code is active.
Symptoms
- Reduced power, flat acceleration or limp mode under load
- MIL on, sometimes with additional boost control or overboost codes
- Audible hiss or a whistling leak from the charge pipework when a boost leak is the cause
- Black smoke on diesels under acceleration
- Inconsistent boost readings in live data compared with the manifold pressure sensor
Likely causes
- Sensor port or the pressure passage partially blocked with oil, soot or condensation, so it damps and lags the real pressure
- Drifted sensor that no longer matches barometric pressure at key-on
- Boost leak between the compressor and the sensor location, so the sensor genuinely sees less pressure than the model expects
- Charge pipe or clamp loose, or a split hose that opens only under load
- High resistance in the signal or ground circuit shifting the reported value
- Faulty manifold pressure or barometric sensor making the comparison fail even though this sensor is good
- Wastegate, vane actuator or bypass valve not holding its commanded position, so real boost differs from the target
How to fix it
- With the key on and the engine not running, compare this sensor, the manifold pressure sensor and barometric pressure; all three should read within a small band of each other
- Log the sensor against manifold pressure and commanded boost during a road test to see where the two diverge
- Pressure-test the charge air system to find leaks at hoses, clamps, the cooler and the sensor seal
- Remove the sensor and clean or inspect the port for oil and carbon build-up
- Check the signal and ground circuits for added resistance and check the reference voltage under load
- Verify that the wastegate or variable vane actuator reaches its commanded positions
- Replace the sensor once leaks, blockage and wiring have been excluded, then confirm the values track correctly through the boost range