Powertrain, generic (extended)

P2578 Turbocharger/Supercharger Speed Sensor A Circuit

Check engine lightOn
EmissionsRelevant
Drive cycleNot required
Limp modePossible

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.

Likely causes

Loose, corroded or oil-soaked connector at the speed sensor
Harness chafed or heat-damaged near the hot turbocharger housing
Internal failure of speed sensor A
Fault in the engine control module input stage

Symptoms

  • Malfunction indicator lamp on
  • Reduced power because boost is limited as a precaution
  • Turbo speed missing or frozen in live data

Repair estimate

DifficultyMediumWorkshop job
Parts and labour€80–600
Time0.5–3 h

Typical range across vehicles; the real cost depends on what the testing finds.

Parts involved

turbo speed sensor asensor wiring

Related codes

P2579P2580P2581P2582P2593

References: law.cornell.edu, static.nhtsa.gov.