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P0128: Coolant temperature below thermostat regulating temperature
Low urgencySystem: Cooling
What P0128 means
The engine is not reaching normal operating temperature in the expected time. A thermostat stuck open is the most common reason.
Common symptoms
- Weak heater, engine slow to warm up
- Worse fuel economy
- Failed emissions test
Common causes
- Thermostat stuck open
- Faulty coolant temperature sensor
- Low coolant or air in the cooling system
Can I keep driving?
Low urgency. Usually safe to drive for now. Have it looked at at your next service, and check the simple things first.
What to do next
- Write down the code and any symptoms you notice.
- Check the simple things first: the fuel cap, loose connectors and fluid levels where they apply.
- Do not just clear the code. If the light comes back, the cause is still there and needs a proper diagnosis.
- Read live data and freeze frame data with an OBD-II scanner app to see what the car was doing when the code was set.
Read P0128 from your own car
DriveHub connects to a $15 to $30 OBD-II adapter, reads the code from your car and explains it in plain English. iPhone and Android.
General information, not a diagnosis. Causes vary by make, model and engine. If you are unsure, have the car inspected.