P012A: Turbocharger/Supercharger Inlet Pressure Sensor A Circuit
What to do
Ask when the air filter was last changed, and mention it if it is overdue. This sensor's job is largely to notice a restricted intake, so a filter choked with debris is a real possibility and one of the cheapest things on the list.
Mention if the car has been driven in heavy snow or through deep standing water, since a blocked or wet intake produces genuine readings that look like a fault.
Expect turbocharger-related codes alongside this one. They are often consequences — the module uses this sensor to judge whether the turbo is performing, so it cannot make that judgement while this is faulty.
The car will usually drive normally, though it may limit boost as a precaution.
What this code means
A general electrical fault has been detected in the turbocharger inlet pressure sensor circuit.
The name misleads almost everybody, so it is worth being exact: this sensor measures the pressure going into the compressor, not the boost coming out of it. It sits between the air filter and the turbocharger, in a region that is at or slightly below atmospheric pressure — the compressor pulls a small depression as it draws air in.
Which makes it a restriction gauge more than a boost gauge. The module compares it against barometric pressure, and a growing difference means something is choking the intake: a blocked air filter, a collapsed intake hose, a snow-packed grille, or a plastic bag drawn onto the intake mouth.
Knowing the pressure at both ends of the compressor also lets the module compute a pressure ratio, which is how it judges whether the turbocharger itself is delivering what it should. So a fault here disables that judgement, and turbocharger performance codes often follow as a consequence rather than as separate faults.
A general circuit code is the least specific member of its family. Where a low, high or range/performance code is stored alongside, that one carries the useful information.
Check the connector before the sensor. It lives in the engine bay near the intake with the usual exposure to heat, vibration and oil mist.
Likely causes
Start here
Less common
- Restricted air filter · easy
- Damaged wiring harness · moderate
- Oil in the sensor connector · easy
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.
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