Cooling · Severity: Low
P0128 — Coolant Thermostat Below Regulating Temperature
The engine takes too long to reach operating temperature.
Common symptoms
- Temperature gauge stays low
- Poor heater output
- Higher fuel consumption
Likely causes
- Thermostat stuck open
- Faulty coolant temperature sensor
- Low coolant level
- Cooling fan running constantly
First test to run
Log coolant temperature from a cold start; if it stalls below ~80 °C while the radiator hose warms early, the thermostat is open.
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