P0125 Nissan Altima
Insufficient Coolant Temperature for Closed Loop · Powertrain Code · Medium · Repair: Moderate
What is P0125?
The engine is not reaching operating temperature quickly enough for the ECM to enter closed-loop fuel control. Usually caused by a stuck-open thermostat.
When the Nissan Altima triggers code P0125 (insufficient coolant temperature for closed loop), it typically points to an issue in the powertrain system. Below you'll find the most common causes, symptoms, and repair options specific to the Nissan Altima.
This repair is rated moderate, meaning some experience and specialty tools required.
Diagnostic data on this page is compiled from publicly available repair resources and technical service bulletins. Always have a qualified mechanic confirm the diagnosis before authorizing repairs on your Nissan Altima.
Common Causes on Nissan Altima
- Stuck-open thermostat preventing engine from reaching operating temp
- Failed ECT sensor giving inaccurate readings
- Low coolant level allowing air pockets
- Thermostat housing leak (common on QR25DE)
Symptoms
- Check Engine Light on
- Engine very slow to warm up
- Heater blows lukewarm
- Poor fuel economy in cold weather
- Temperature gauge stays low
Notes for Nissan Altima
When replacing the thermostat on QR25DE engines, also inspect the housing for hairline cracks that cause slow leaks.