P0128 Code: Meaning, Causes, and Symptoms | OBD2 Codes
P0128 – Coolant Thermostat Malfunction
P0128: DIY Repairing Video Tutorial
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P0128 Possible Causes
Leaking or stuck open thermostat
Low engine coolant level
Insufficient warm up time
Faulty engine coolant temperature sensor
Engine coolant temperature sensor harness is open or shorted
Engine coolant temperature sensor circuit poor electrical connection
P0128 Possible Symptoms
Engine Light ON (or Service Engine Soon Warning Light)
The thermostat is a component that blocks the flow of coolant to the radiator until the engine has warmed up. When the engine is cold, no coolant flows through the engine. Once the engine reaches its operating temperature, the thermostat opens. The OBDII sets when the engine coolant temperature has not risen enough to open the thermostat even though the engine has run long enough. This is due to a leak in the seal or the thermostat open stuck.