p0128
Easy Fix
Toyota · Sedans
Coolant Thermostat Below Regulating Temperature
Quick Answer
Error code P0128 on your Toyota Sedans means: Coolant Thermostat Below Regulating Temperature. This is usually fixable — see the step-by-step guide below.
Affected Models
Applies to all models
Avalon XLE 2022Camry XSE 2024Camry Hybrid SE 2024Corolla SE 2024Corolla Hybrid LE 2024Crown Platinum 2024Mirai Limited 2024Prius XLE 2024Camry LE 2023Camry LE 2024Camry SE 2023Camry SE 2024Camry TRD 2024Camry XLE 2024Corolla LE 2023Corolla LE 2024Corolla XSE 2024Crown Limited 2024Crown XLE 2024Prius LE 2024Prius Limited 2024
Likely Causes
How to Fix It
1
Check coolant level and top off if low; inspect for leaks
2
Use a scan tool to monitor engine coolant temperature during warm-up and compare to actual temperature with a thermometer
3
Verify the radiator fan is not running continuously at cold start
4
Replace the thermostat if the engine takes too long to reach operating temperature
5
Refill coolant and bleed air from the cooling system after thermostat replacement
Pro Tip
This is a common issue that most users can resolve without specialized tools. Try the first step before moving on to more complex solutions.
Parts You May Need
Thermostat
Thermostat housing gasket
Engine coolant
ECT sensor (if faulty)
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