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Diagnose/P0178
P0178Low SeverityFuel System

Fuel Composition Sensor Circuit Low Input

What This Means

The fuel composition sensor voltage is below the minimum expected threshold. This sensor detects ethanol content in flex-fuel vehicles to adjust fuel delivery for different fuel blends.

Common Symptoms

  • Check engine light on
  • Poor performance with E85
  • Fuel economy changes
  • Hard starting

Common Causes

  • Faulty fuel composition sensor
  • Wiring damage
  • Connector corrosion
  • Contaminated sensor
  • PCM circuit issue

Estimated Repair Cost

$100 – $400
Parts and labor (varies by vehicle and location)
Difficulty:Moderate

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For informational purposes only. Diagnostic trouble codes are starting points for diagnosis, not definitive answers. Always consult a certified mechanic for proper diagnosis and repair. Estimated costs vary by vehicle, location, and shop rates.