P012B: Turbocharger/Supercharger Inlet Pressure Sensor A Circuit Range/Performance
What to do
Ask for the air intake to be inspected before the sensor is replaced — the filter, the airbox and the hose between it and the turbocharger. This sensor measures how hard the engine is having to suck, so a blocked filter or a collapsing hose produces this fault while the sensor is working perfectly.
Mention when the air filter was last changed, and say if a non-standard filter or induction kit has been fitted, since a badly fitted one causes this directly.
Say whether the car feels flat under hard acceleration but normal otherwise. That pattern suggests the restriction is real rather than the reading being wrong.
Mention any rodent activity or nesting material found under the bonnet, which is a genuine and surprisingly common cause of a blocked airbox.
What this code means
The turbocharger inlet pressure sensor is reporting a value that is electrically valid but does not fit the conditions.
This is the member of the family where the sensor is most often innocent, and understanding why prevents an expensive mistake. The module knows roughly what pressure ought to exist ahead of the compressor: close to barometric at idle, a little below it under heavy draw. When the measured value sits outside that expectation, the sensor gets blamed — but a genuinely restricted intake produces exactly the same reading.
So the first question is whether the depression is real. A blocked air filter, a collapsed or delaminated intake hose, a mouse nest in the airbox, or an aftermarket filter fitted badly all pull the pressure down for honest reasons. The sensor is reporting the truth about a restriction nobody has looked for.
The cheap and conclusive check is at rest. With the engine off, this sensor must read barometric pressure, and it must agree with the manifold pressure sensor and the barometric sensor to within a small margin. Three sensors that should read the same and one that does not is the answer — and it takes seconds.
Where it agrees at rest and disagrees under load, look for the restriction rather than at the sensor.
Expect boost or turbocharger performance codes alongside, because the pressure ratio the module computes from this sensor is how it judges the turbocharger.
Likely causes
Start here
- Restricted air filter · easy
- Split or cracked intake hose · easy
- Faulty turbocharger inlet pressure sensor · easy
Less common
- Sensor drifted out of calibration · easy
- Rodent damage to wiring · moderate
Symptoms
Components involved
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.
Community experience
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