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Diagnose/P0139
P0139Medium SeverityEmissions

O2 Sensor Circuit Slow Response (Bank 1, Sensor 2)

What This Means

The downstream oxygen sensor on bank 1 (after the catalytic converter) is switching between rich and lean readings too slowly. This sensor is used to monitor catalytic converter efficiency.

Common Symptoms

  • Check engine light on
  • Failed emissions test
  • No driveability change
  • Higher emissions

Common Causes

  • Faulty O2 sensor
  • Damaged wiring or connector
  • Exhaust leak near sensor
  • Catalytic converter degradation
  • PCM circuit failure

Estimated Repair Cost

$150 – $500
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.