P0128Coolant Thermostat Below Regulating Temperature
The engine has been running long enough to reach operating temperature, but coolant temperature stayed below the thermostat's regulating value. Almost always caused by a thermostat stuck open. Costs fuel economy and increases cold-engine emissions.
This code also has a manufacturer-specific definition:
Can I keep driving? With caution
You can drive to the shop, but do not postpone the repair. The problem may worsen and damage other components.
Sistema Afectado
Aire / Combustible · Inyección, MAF, MAP, O₂
Relacionado con la mezcla aire-combustible: sensores de flujo, presión, inyectores o bomba.
Espacio para vendedores de repuestos
Aún no hay un anunciante en este espacio.
Possible Causes
The components or conditions that trigger this code
- 1Thermostat stuck open Coolant sensor reading low
How to Fix It — Step by Step
Recommended diagnostic and repair procedure
- 1Difficulty: medium. Estimated time: 0.7-3 hours. Estimated cost: €50-€
- 2DIY possible
Note: This information is for general reference. For precise diagnostics and safety repairs, always consult a certified mechanic.
Estimated Cost
Approximate range in USD (varies by region and shop)
Sensors + injectors
* Diagnosis only: $50–$150
Quick Info
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