Cause
Boost leak in charge pipework
Pressurised air escaping from the ducting between the compressor and the engine, so the boost the turbocharger genuinely produces never reaches the cylinders. The control module sees a target it cannot meet and blames the part it commands — the wastegate, the vane actuator, the turbocharger itself — which is why a leak so often ends with an expensive part replaced and the fault still present.
It is frequently audible before it is measurable. A whistle or a chuff under load that is absent at idle is the leak opening as pressure rises, and it is worth listening for before anything is connected.
The tell in the data is the disagreement between two measurements. A turbocharger working into a leak still spins hard and its own speed or compressor-outlet reading looks healthy, while the manifold pressure downstream falls short. Two boost readings that disagree with each other locate the leak between them, and that is more useful than either reading alone.
Where it leaks is predictable. A charge hose relaxing off its stub under pressure, a clamp that was never retorqued after a service, a split on the underside of a bend, a perished intercooler end-tank seal, or a sensor grommet not seated. Pressure-test the system cold rather than hunting it running — a leak that only opens under boost is silent at idle, which is precisely why it survives an inspection.
Typically a moderate job.
Some of these codes mean you should stop driving
3 of the 21 codes this can cause indicate a fault where continuing to drive risks damage or is unsafe. Which one you have matters more than the cause does — read the code's own page before deciding.
Codes this can cause (21)
Codes where this is a likely explanation first, rather than merely a possible one.
- P0046 Turbocharger/Supercharger Boost Control A Circuit Range/Performance Likely for this code High
- P0049 Turbocharger/Supercharger A Turbine Overspeed Likely for this code Stop driving Critical
- P0236 Turbocharger/Supercharger Boost Sensor A Circuit Range/Performance Likely for this code High
- P0240 Turbocharger/Supercharger Boost Sensor B Circuit Range/Performance Likely for this code High
- P0299 Turbocharger/Supercharger A Underboost Condition Likely for this code High
- P032F Combustion Engine Producing Insufficient Torque Likely for this code High
- P2074 Manifold Absolute Pressure/Mass Air Flow — Throttle Position Correlation at Higher Load Likely for this code Moderate
- P2262 Turbocharger/Supercharger Boost Pressure A Not Detected — Mechanical Likely for this code High
- P2263 Turbocharger/Supercharger A Boost System Performance Likely for this code High
- P2579 Turbocharger/Supercharger Speed Sensor A Circuit Range/Performance Likely for this code Stop driving High
- P2594 Turbocharger Speed Sensor B Circuit Range/Performance Likely for this code Stop driving High
- P2ADF Intake Air System Leak Bank 2 Likely for this code Moderate
- P0096 Intake Air Temperature Sensor 2 Circuit Range/Performance Bank 1 Moderate
- P0235 Turbocharger/Supercharger Boost Sensor A Circuit High
- P0239 Turbocharger/Supercharger Boost Sensor B Circuit High
- P2281 Air Leak Between Mass Air Flow Sensor and Throttle Body Moderate
- P2A0A Manifold Absolute Pressure Sensor B Circuit High
- P2A0B Manifold Absolute Pressure Sensor B Circuit Range/Performance High
- P2A0C Manifold Absolute Pressure Sensor B Circuit Low High
- P2A0D Manifold Absolute Pressure Sensor B Circuit High High
- P2A0E Manifold Absolute Pressure Sensor B Circuit Intermittent/Erratic High
Information, not instruction
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Have anything you intend to act on checked by a trained person against the manufacturer's own procedure for your vehicle. Nothing here replaces that procedure.
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