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I have a 2009 Chevy Malibu lt 2.4L and the temp gauge will drop while driving or it wont even read that the engine is at operating temp but the ac blows cold air and I got a scan tool and no codes were tripped so i hit reset all codes and the needle went up to operating temp and I replaced the coolant temp sensor any clue what it could be

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  • Welcome to Motor Vehicle Maintenance & Repair! Oct 17, 2021 at 18:52
  • Perhaps there was no fault. Try driving hard uphill for several miles and see if the gauge stays at normal or normal plus a bit. Then drive down and see if it goes below normal. If so then it seems fine.
    – Solar Mike
    Oct 17, 2021 at 19:10
  • so say i start it the temp gauge does the thing where it goes up and down like all of the gauges do then it will stay down or it'll go up while i drive it then it'll go down and read cold then stay down the the cold air works Oct 17, 2021 at 19:48
  • AC blowing cold air has nothing to do with it.
    – Solar Mike
    Oct 17, 2021 at 20:20
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    i heard that it could have been the bcm if cold air blew then it wasnt the bcm but if the fans turned on but no cold air blew then i would have to run a test to see hat part of the bcm needs to be fixed but since cold air blows its not the bcm Oct 17, 2021 at 20:23

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First check to ensure you have enough coolant. Air pockets around the sensor will cause erratic readings. I've never seen a code get thrown for lack of coolant in the radiator. If it's low, check for a leak.

If it's full, do a pressure test to ensure it's holding the pressure it should. My next guess would be a faulty sensor but you've just replaced that. Check for damaged wires leading from the sensor to the wiring harness.

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  • Why the downvote? I've had every one of these things cause an erratic temperature sensor reading. If you're going to leave a downvote, leave a comment as to why my answer doesn't meet your standards. Apr 14, 2023 at 13:51

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