Coolant temperature staying low

[davalc89]

Hi,

My coolant temperature rarely now goes to operating range. When it gets there i'll will come down to around 75 celsius. Sometimes it slowly wobble back and forth between 75 and 90. This is all in mixed road and highway speed. Electric fan is not working all the time. I'm thinking thermostat. Has anybody ever had a bad temperature sensor?

Thx

[06T200]

No but I had a thermostat that was too cold for the ECM, it threw a P0128 code if I recall correct, once I replaced it with a 190 thermostat it had been fine.

[Daox]

I'd bet thermostat. They're a common item to go on cars. Much more common than a temp sensor. Cheaper to replace too.

[davalc89]

I've got an update on the situation. Today the temp gauge pretty much drop to the bottom and code p0128 came up. Any idea to diagnose the temp sensor and make sure it's not the culprit?

Thx

[06T200]

Does your scan tool give you the engine temp values to see what it is seeing? Before you begin the long journey to the temp sensor did you replace the thermostat with a new one? I have to ask, as simply getting to the coolant temp sensor will be the biggest challenge as it is underneath the intake manifold. You will need to get at it from under the car and measure the resistance at the sensor. The thermostat however is a five minute swap and should fix it.

[davalc89]

I thought the sensor was the one on the thermostat housing. If it isn't, what is it?

[06T200]

Sorry, I assumed you were working on an 04-07 Aveo.... My bad. When I don't know the year Aveo you are working on, I am really just shooting in the dark with your questions. I have no experience on Aveo's past 07MY, so ignore my comments.

[06T200]

FWIW: There is no test procedure for the temp sensor, at least not for pre 07 models. If you could let me know what year you are working on I could look up to see if there is a test process for yours.

[davalc89]

It's a 2010 thx

[06T200]

test procedure:

Note:
A thermometer can be used to test the sensor off the vehicle.

Test the ECT sensor by varying the sensor temperature while monitoring the sensor resistance. Compare the readings with the Temperature Versus Resistance table and verify that the resistance is within 5 percent of the specification.




Temperature Versus Resistance
See attachment, can't post the table here...