P0125
Low SeverityInsufficient Coolant Temperature for Closed Loop Fuel Control
Cooling System
What Does P0125 Mean?
The engine is not reaching proper operating temperature for the fuel system to go into closed-loop mode. Typically a stuck-open thermostat.
Common Fix
Replace thermostat
Estimated Cost (DIY)
$15 - $40
Symptoms
- ⚠️Poor fuel economy
- ⚠️Heater blows lukewarm
- ⚠️Temperature gauge stays low
- ⚠️Check engine light
Related Symptoms
Common Causes
How to Diagnose P0125
- 1Check if engine reaches operating temp (190-210°F)
- 2Compare ECT sensor reading to actual temp
- 3Inspect thermostat
- 4Replace thermostat if stuck open
OEM Diagnostic Flowchart
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Open the exact vehicle hub for a repair workflow commonly associated with P0125.
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Related Codes
The engine is not reaching normal operating temperature within the expected time. The thermostat is almost certainly stuck open.
The ECT sensor reading is not changing as expected during warm-up. Either the sensor is lazy or the thermostat is preventing normal warm-up.
The ECT sensor circuit has a general malfunction. This sensor tells the ECM how warm the engine is for fuel, timing, and fan control.
Frequently Asked Questions
- Is P0125 the same as P0128?
- Very similar. P0125 means the ECM cannot enter closed-loop fuel control. P0128 means the coolant has not reached expected temp within a time limit. Both usually mean a stuck thermostat.
- Can I drive with P0125?
- Yes, but fuel economy suffers and your heater will not work well in winter. Replace the thermostat soon.
Related Repair Guides
If your vehicle has triggered P0125, these DIY repair guides may help: