P0128: Coolant Temperature Below Thermostat Regulating Temperature
Severity: Low
What it means
The engine takes too long to warm up.
Common symptoms
- Temperature gauge reads low
- Weak cabin heat
- Lower fuel economy
Common causes
- Thermostat stuck open
- Faulty coolant temperature sensor
- Low coolant
What to check first
- Check the coolant level when the engine is cold
- Watch whether the gauge reaches normal after 15 minutes of driving
Causes vary by vehicle. Confirm with testing before replacing parts.
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