Coolant Thermostat Below Temperature
The engine coolant is not reaching the expected temperature within a specified time.
Informational only. Consult a qualified mechanic.
- Stuck-open thermostat
- Low coolant level
- Faulty ECT sensor
Replace the thermostat. This is a common and inexpensive repair.
What does P0128 mean?
The P0128 OBD-II diagnostic trouble code (DTC) indicates: coolant thermostat below temperature. This is a low-severity powertrain code that your vehicle's onboard diagnostics system triggers when the engine coolant is not reaching the expected temperature within a specified time. If your check engine light is on with this code, the vehicle is generally safe to drive, but you should have it inspected soon.
Use Your Service Book to log this diagnostic trouble code to your vehicle's service history, track repairs, and get maintenance reminders — all for free.
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