Coolant Thermostat Below Regulating Temperature
The engine is staying too cold for too long after startup. This usually means a thermostat is stuck open, the coolant level is low, or a temperature sensor is giving false readings.
You can usually drive short distances, but the engine may run inefficiently and heater performance may be poor. If the temperature gauge stays low, the coolant level is low, or the engine starts overheating, stop driving and diagnose it right away.
P0128 means the powertrain control module has detected that engine coolant temperature is not rising to the expected range within a specified time. The most common cause is a thermostat stuck open, but low coolant, a faulty coolant temperature sensor, an intake air temperature sensor issue, or a cooling fan that runs continuously can also trigger it.
Yes. A thermostat stuck open is the most common cause of P0128.
Usually no, but it can if the cooling system has other problems. A thermostat stuck open more often causes the engine to run too cool.
Yes. Low coolant can make the temperature reading incorrect and delay normal warm-up.
No. The car may still run, but fuel economy, heater performance, and emissions can get worse, and the underlying cooling issue may grow.