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Diagnose/P0409
P0409Medium SeverityEmissions

Exhaust Gas Recirculation Sensor A Circuit Intermittent

What This Means

The EGR (Exhaust Gas Recirculation) system sensor or control circuit has a malfunction. This circuit monitors and controls EGR valve position for proper exhaust gas recirculation.

Common Symptoms

  • Check engine light on
  • Engine knocking or pinging
  • Rough idle
  • Failed emissions test

Common Causes

  • Carbon buildup in EGR passages
  • Stuck or failed EGR valve
  • Faulty EGR position sensor
  • Vacuum supply issue
  • Wiring damage

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.