P2578
Turbocharger/Supercharger Speed Sensor A Circuit
General electrical fault on the turbocharger/supercharger shaft speed sensor A — a high-frequency Hall or eddy-current sensor on the compressor shaft. The ECM uses turbo speed for overspeed protection (typically 200,000+ rpm) and for closed-loop boost on VGT systems. With no valid speed the ECM limits boost.
- Check engine light: Yes
- Emissions related: Yes
- Repair difficulty: medium
Symptoms
- Check engine light on
- Significant power loss / limp mode
- Possible blue or black smoke from exhaust
- Whistling or hissing sound from intake
Common causes
Ordered by how often each turns out to be the cause.
- Open or shorted wiringCommon
- Aged sensor with reduced output amplitudePossible
Parts involved
- Turbo Speed Sensor A
- Sensor Wiring
P2578 is a generic OBD-II code defined by SAE J2012. Exact wording and diagnostic procedure vary by manufacturer and model. Code definitions are drawn from the public-domain OBDex dataset; the workshop notes are our own.