When the code is set
The ECM monitors how quickly the coolant warms up after the engine starts, taking the outside temperature and engine load into account. If the coolant does not reach the specified temperature in the expected time, it stores P0128.
Can I keep driving?
Usually safe to drive
P0128 is usually not urgent and you can keep driving. Still have it fixed, because a cold engine uses more fuel and wears faster, and the heater works less well in winter. If the temperature gauge shows overheating or the red temperature warning light comes on, stop.
Symptoms
- The check engine light is on, often with no other symptoms.
- The temperature gauge rises slowly or drops on the motorway.
- The cabin heater is less effective.
- Higher fuel consumption.
Common causes
- A thermostat that sticks open or does not seal – the most common cause.
- A faulty coolant temperature sensor or its connector.
- Low coolant level.
- A radiator fan that does not switch off.
- Outdated engine control module software (on some models).
How to find the cause
A mechanic usually works like this:
- Check the coolant level.
- Read the sensor temperature with the engine cold; it should be close to the outside temperature.
- On a drive, watch how quickly the coolant warms up and whether it reaches operating temperature.
- Check whether the radiator hose warms up too early, which points to a thermostat stuck open.
Other ways the code is written
Scan tools and workshop printouts sometimes show the code with extra characters:
- P012800
Related codes
Frequently asked questions
Evoca fault code diagnostics is an informational aid and does not replace a professional inspection of your vehicle. Only an inspection of the vehicle at a workshop can confirm the cause of a fault.
Check P0128 for your car
Enter the code and, if you like, your car details. You get a free report with possible causes and next steps by email.