P0139 – O2 Sensor Slow Response (Bank 1 Sensor 2)

Description

The ECM detects a slow response from the downstream O2 sensor.

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Symptoms

  • Poor fuel economy
  • Check engine light

Causes

  • Aging O2 sensor
  • Exhaust leaks

Diagnosis

  • Monitor O2 switching
  • Inspect exhaust

Repair

  • Replace O2 sensor
  • Fix leaks