P2578Turbocharger/Supercharger Speed Sensor A Circuit
- Generic OBD-II code · Powertrain
- Turns on the check-engine light
- Matters for the ITP
- Can trigger limp mode
- How the car detects it
- P2578 is the catch-all electrical fault for speed sensor A, the pickup that counts revolutions of the turbocharger or supercharger shaft, normally by sensing a tone feature on the compressor wheel or its nut. The engine computer logs it when the sensor line is faulty in a way it cannot classify as too low, too high or sporadic; those cases have their own codes P2580, P2581 and P2582, and P2579 covers a readable but implausible speed. No manufacturer documents P2578 publicly with thresholds. CARB requires electronic parts used for boost control to be monitored as comprehensive components, and Bentley's W12 bulletin on its two shaft speed sensors calls for checks for an open line, shorts to ground or battery and shorts between wires. Boost may be limited and the warning lamp is usually on.
- What you may notice
- Malfunction indicator lamp on
- Reduced power because boost is limited as a precaution
- Turbo speed missing or frozen in live data
- Likely causes
- LikelyLoose, corroded or oil-soaked connector at the speed sensor
- PossibleHarness chafed or heat-damaged near the hot turbocharger housing
- PossibleInternal failure of speed sensor A
- RareFault in the engine control module input stage
- Inspection (ITP)
- Matters for the ITP. While the check-engine light is on, the car fails the emissions check.
- Repair
- Medium · Usually a job for a workshop.Typical cost: €80 – €600
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.