P0128
GENERIC DTC · Cooling
Coolant thermostat temperature below regulating temperature
Ce que le code signifie
The engine did not reach the modeled operating temperature in the expected time.
Gravité et conduite
Service soon; stop if actual overheating occurs
Causes possibles
- Thermostat stuck open
- Coolant-temperature sensor bias
- Low coolant from a leak
- Extreme conditions or cooling-fan control
Prochaines vérifications
- Never open a hot cooling system
- Compare scan temperature with actual cold-soak temperature
- Inspect for visible leakage only when fully cool
Source et limite
Code structure follows SAE J2012. Manufacturer-specific definitions, pinpoint tests, wiring, torque, fluids, and repair procedures require authoritative information for the exact vehicle.
SAE J2012 Diagnostic Trouble Code DefinitionsReviewed 2026-08-13