What it means
The ECM detects a range/performance fault on the turbocharger/supercharger a temperature sensor. Reading cannot be used reliably for control.
At a glance
- Usually lights the check-engine light
- Affects emissions; the car can fail an emissions test
How it works
Turbocharger or supercharger A’s temperature sensor helps the engine control module manage heat in the forced-induction system. P2B71 sets when the sensor signal is electrically plausible but its temperature reading is outside the expected range or does not track conditions correctly, which can point to a drifting, displaced, or aged sensor.
Common causes
Most likely first.
- Sensor characteristic drifted
- Sensor mounting displaced
- Sensor element aged beyond calibration window
Symptoms
- Check engine light on
- Significant power loss / limp mode
- Possible blue or black smoke from exhaust
- Whistling or hissing sound from intake
How to diagnose it
- Record freeze-frame data and compare sensor A’s live temperature reading with ambient temperature when cold and with operating conditions as the system warms.
- Inspect sensor A’s mounting and connector to confirm it is seated in the intended position and has no damage or contamination.
- Check the sensor harness for chafing, poor connections, or heat damage that could distort the reading without causing a clear open or short.
- Compare sensor A’s readings with related intake or forced-induction temperature data under similar conditions for implausible differences.
- Test the sensor response over changing temperatures using the manufacturer’s procedure and compare it with the manufacturer’s specification.
Common fixes
- Secure sensor A in its correct mounting position.
- Clean and secure a poor sensor A connector or repair damaged wiring.
- Replace turbocharger or supercharger A’s temperature sensor if its output drifts outside specification.
- Correct a confirmed intake or charge-air leak if it is contributing to abnormal temperatures or symptoms.
Can I keep driving?
Avoid hard acceleration and sustained boost while the temperature reading is unreliable, especially if power is reduced or smoke appears. Incorrect temperature feedback can impair forced-induction control, and continued operation under heavy load may aggravate an underlying problem.
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.