Error Code P0128 - Thermostat or Temp Sensor
 

Hi everyone, last week engine check wit error code P0128 and it likely Thermostat malfunction. I replaced new Mahle Thermostat on Monday and after 3 days driving, tonight the engine check and scanning error code P0128 again. I diagnostic and clear the code and restart the engine, the engine check light is gone.

However, the scanning tool software still show "PERMANENT" P0128 Coolant Thermostat (Coolant Temperature Below Thermostat Regulating Temperature)

Is the new Thermostat defective? Is the Temperature Sensor fail? (I replaced genuine Temp sensor in January), i filled Coolant on Monday and rechecked coolant level is full.

(I attached the error image below)


Any help?

Thank you!

Read the temp coming out of the radiator see if it's making sense also the oil temp. With those two you should be able to tell if the thermostat is stuck open or the sensor is just whack. Also what does ECT read with scanner? Typically of they fail you'll get a temp like -40° or some crazy max temp. If that's the case def the wiring or the sensor.

New ≠ fixed follow the symptoms even if they point to a new part.

suspect it's the temp sensor. was it genuine bmw?

BMW Temperature Sensor - Genuine BMW 13621433076

How can there be no trouble codes and a permanent code at the same time? Is "permanent" your scanners definition of a shadow code?

Thank you all - I replace coolant temp. sensor again and it has been 2 weeks with out P0128 error.

Would be useful to know, eh?


Bad 3rd world sensor or wire/connector issue my guess