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P0128 OBD-II Trouble Code

Technical Description

Coolant Thermostat (Coolant Temperature Below Thermostat Regulating Temperature)

What does that mean?

This means that the engine's PCM detected that the engine has not reached the required temperature level within a specified amount of time after starting the engine. The intent of the P0128 code is to indicate a faulty thermostat. Similar codes: P0125

In determining the engine did not reach a "normal" temperature, it takes into account the length of time the vehicle has been running, the intake air temperature (IAT) sensor reading, the engine coolant temperature (ECT) sensor reading, and the speed of the vehicle.

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Symptoms

You will likely not notice any drivability problems other than the MIL illumination.

Causes

A code P0128 may mean that one or more of the following has happened:

Possible Solutions

Past experience indicates that the most likely solution is to replace the thermostat. However here are some suggestions on troubleshooting and repairing a P0128 OBD-II code:

Need more help?

If you still need help regarding the P0128 trouble code, please post your question in our auto repair forums.

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