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Fault code

P0128 fault code.

This code comes up with one known fault.

Generic code

Code type

Engine and drivetrain

System

The engine does not reach operating temperature

The engine control unit compares the coolant temperature with the running time. The engine did not warm up within the expected time. The typical cause is a thermostat stuck open, but a bad temperature sensor can also cause it. A cold engine burns more fuel, and the cabin heating stays weaker.

The code tells you what the control unit measured, not which part has failed. The same code has several possible causes.

Which known faults it comes up with

M270: a failing electric thermostat leaves the engine cold

expensive

The electric thermostat can fail from 90 000 kilometres and sticks open. The coolant then circulates in the large circuit even while the engine should still be warming up, so the engine does not reach its 80 degree operating temperature.

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The control unit logs it too: code P0128 means that the coolant temperature stays below the regulating temperature of the thermostat. The symptom is that the engine does not warm up properly even after a long time, the heater is lukewarm, consumption rises and the engine management light comes on as well.

An engine running cold for a long time wears faster, because cold oil does not lubricate the same way and fuel dilutes it in a greater proportion. The thermostat is built into the coolant circuit, so its replacement involves draining coolant.

above 90,000 km

What to check

  • Run the engine for ten minutes: the temperature gauge has to reach its usual middle value
  • Turn the heating on: the air should be hot, not lukewarm
  • Have the fault codes read and look for P0128
2 more steps in the write-up

Information, not an expert opinion

We write the descriptions, and we put the source next to them. A person reviews them before they go out. They are still information, not a technical expert opinion.

  • A fault on the list does not mean the car you are looking at has it.
  • A fault missing from the list does not mean the model is fault-free. Write-ups are made model by model. Not all of them are done.
  • You decide whether to buy. This is no substitute for an inspection. That needs a workshop and a history check.
Details in the terms