P0125 - Insufficient Coolant Temp for Closed Loop

Engine did not reach closed-loop temperature in expected time.

Code Overview

Engine did not reach closed-loop temperature in expected time.

Common Causes

• Thermostat stuck open
• Low coolant level or trapped air in the cooling system
• ECT sensor reading colder than actual
• Cooling fan running too much or too early

Symptoms

• Weak cabin heat in cool weather
• Extended warm-up before closed loop
• Reduced fuel economy from staying in warm-up strategy too long

Diagnostic Steps

1. Review the coolant warm-up curve from a cold start on the scan tool
2. Inspect thermostat operation and housing for signs of poor sealing
3. Verify coolant level and bleed air from the system if needed
4. Check whether the cooling fan is running when it should not

Repair Difficulty

Moderate

General difficulty estimate for the most common repair path.

Likely Repairs & Cost Guides

Use test results to confirm the fault before pricing the repair.

Related OBD Codes

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Next Steps

Move from the code to a diagnosis path, then into repair pricing once the fault is confirmed.