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Diagnose/P0125
P0125Low SeverityEngine

Insufficient Coolant Temperature for Closed Loop

What This Means

The engine is not reaching the minimum temperature required for the fuel system to enter closed-loop operation. The computer needs a warm engine to use O2 sensor feedback for precise fuel control.

Common Symptoms

  • Poor fuel economy
  • Higher emissions
  • Slow warm-up
  • Check engine light on

Common Causes

  • Thermostat stuck open
  • Faulty ECT sensor
  • Low coolant level
  • Cooling fan always on
  • Very cold ambient conditions

Estimated Repair Cost

$75 – $350
Parts and labor (varies by vehicle and location)
Difficulty:Easy

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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.