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P0128: Coolant Thermostat Below Regulating Temperature
The engine is taking too long to reach normal operating temperature.
Common causes
- Thermostat stuck open
- Low coolant
- Bad coolant temperature sensor
- Cooling fan running when it should not
This free page explains the code. A Shop Brief adapts the next steps to your year, make, model, and full code stack.
Related codes:
P0113P0455P0420 Pricing Sample brief