P0128Toyota YarisYears: 1996 - 2026
Coolant Thermostat (Coolant Temperature Below Thermostat Regulating Temperature)
Reviewed by ASE Certified Technician
What does this mean?
Code P0128 indicates the engine coolant temperature has not reached the thermostat's regulating temperature within a specified time after starting.
Disclaimer: This diagnostic code is part of the standard OBD2 system and can apply to Toyota Yaris models manufactured from 1996 to 2026. However, please note that the presence of this specific code depends on your vehicle's exact engine configuration, options, and production year.
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Common Causes
Faulty or stuck thermostat
Faulty Engine Coolant Temperature (ECT) sensor
Coolant leak or low coolant level
Symptoms to Watch For
- Check Engine Light is illuminated
- Decreased fuel economy
- Engine stalls when cold
- Coolant temperature warning light on