P1139 – O2 Sensor Lean (BMW)

Description

P1139 BMW indicates the O2 sensor detects a lean mixture.

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Symptoms

  • Rough idle
  • Hesitation
  • High fuel trims

Causes

  • Vacuum leak
  • Weak fuel pump
  • Sensor failure

Diagnosis

  • Check fuel trims
  • Inspect vacuum lines
  • Test fuel pressure

Repair

  • Fix vacuum leaks
  • Repair fuel system
  • Replace sensor

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