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Ron, ASE Certified Technician
Category: Mercedes
Satisfied Customers: 33097
Experience:  ASE Certs.
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P0128: Coolant Thermostat (Coolant Temperature Below

Customer Question

P0128: Coolant Thermostat (Coolant Temperature Below Thermostat Regulating Temperature)
Submitted: 5 months ago.
Category: Mercedes
Expert:  Ron replied 5 months ago.

Hello and thank you for your question,

Can you tell me what model and engine size your 2005 Mercedes has please?

Customer: replied 5 months ago.
e320 6 cylinder
Customer: replied 5 months ago.
coolant temp. sensor right
Expert:  Ron replied 5 months ago.

Thank you for that,

In most cases providing the cooling system is full and there is no trapped air this code sets due to a thermostat being stuck open. When the thermostat sticks open it dose not allow the engine to reach the correct temperature and this code will set.