[iflyil]

Hey everyone, I’m having a challenge with my Malibu hybrid. 2018 120,000 miles. The other day after I started it remotely, when I got in and pushed the button the temp gauge stayed cold and the radiator fan kicked on and the battery only hybrid function didn’t work. Engine constantly ran never went full hybrid. I drove home 25 miles and the heat worked fine and did warm up. Drove it like that close and cautiously for a couple days trying to get a CEL to pop up. The radiator fan would run for a few minutes after I shut down the car. So I decided to pull the negative terminal off of the 12v battery and let it sit for a bit before reconnecting. When I reconnected it, the temp gauge read at operating temp where the thermostat would kick on. At this point, the only thing off about the vehicle Is the temp gauge. Hybrid systems worked and heat worked when the car did actually warm up again and no fan. Got in it today and the temp is back at all the way cold and fan running with no hybrid. I could be wrong, but I think I can rule out thermostat stuck shut since heat is working and the engine hasn’t blown, but I think there may be another temp sensor that is telling my car it needs to heat up and keeps the engine running to get to operating temperature separate from one that the thermostat uses. Confused? I am too

 

[Drunken Elvis]

Not sure about the 2018 Hybrid but....earlier versions of the Malibu would do what you describe when the computer lost communication with the engine coolant temp sensor. It would also do this if the computer deemed that the readings from the temp sensor were unreliable. That is...not indicating the expected results. Cause was almost always a bad engine temp sensor. Highly recommend a OEM part. The problem could also be the associated wiring/connectors and or a bad thermostat [not behaving as expected]
Failing Engine Coolant Temp sensor is common. Cheap and easy to try.

 

[iflyil]

Challenge was solved by replacing the coolant temperature sensor.