What it means
The module detects a reading from the turbocharger or supercharger inlet pressure sensor A, downstream of the throttle valve, that is outside the expected range or inconsistent with operating conditions.
At a glance
- Usually lights the check-engine light
- Affects emissions; the car can fail an emissions test
How it works
Sensor A reports pressure in the turbocharger or supercharger inlet passage downstream of the throttle valve. The control module compares that reading with expected values for operating conditions and checks whether it changes plausibly. P012B sets when the circuit is electrically present but the reading is out of range or inconsistent.
Common causes
Most likely first.
- Sensor reading drifted
- Sensor element aged beyond calibration window
- Sensor mounting loose - signal damping
Symptoms
- Check engine light on
How to diagnose it
- Save freeze-frame data and review live sensor A pressure alongside engine speed, throttle position, and other available pressure readings to identify when the mismatch occurs.
- Check that sensor A is firmly mounted in the inlet passage downstream of the throttle valve and that its pressure port is not obstructed.
- Inspect the sensor connector and wiring for looseness, corrosion, damage, or a poor fit that could distort the signal.
- With the engine off, compare sensor A's reading with other pressure readings for plausibility under the same conditions.
- If the mounting and wiring are sound, test sensor A's response as conditions change and compare it with the manufacturer's specification.
Common fixes
- Secure sensor A if its mounting is loose.
- Clean an obstructed sensor pressure port, following the vehicle service information.
- Repair a loose or corroded connector or damaged wiring.
- Replace sensor A if its reading is biased or responds outside the manufacturer's specification.
Can I keep driving?
If the only symptom is the check-engine light, cautious driving is generally possible, but avoid hard acceleration until the pressure reading is checked. An inaccurate reading can impair engine management and may lead to poor running.
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.