P0128 — Coolant Thermostat Below Regulating Temperature
Reviewed1 source
1 source
- Official data (NHTSA)official_feed
What P0128 means
Safe to drive short-term
The engine fails to reach operating temperature within the expected time — most often a thermostat stuck open.
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General information, not a diagnosis or repair instruction. Always confirm with a qualified mechanic for your specific vehicle.
Common causes
- Faulty ECT sensor or its wiring
- Thermostat stuck open
- Low coolant level
Symptoms
- Повышенный расход топлива
- Slow engine warm-up
- Temperature gauge reads low
- Cabin heater blows cold on long drives
- Cooling fan runs constantly
- Weak cabin heat
- Reduced fuel economy
- Increased fuel consumption
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