Engine Temperature Keeps Getting Lost and Fans Run at Full Speed

Mistico3 said:

A few months ago, just as I was getting home, the engine fan started going full speed and I could hear it over my radio. I also noticed that the A/C stopped working and even after I got home and turned the engine off, the fan stayed on for 5 minutes on my 2015 Chevy Tahoe. I had a friend who was a mechanic come and check the truck and saw that there was no temperature reading and explained to me that since the computer could not tell what the temp of the engine was, it went into failsafe mode and engaged the fan at full speed. He told me that it was most likely the sensor and suggested I replace it. Two days later, before I could buy the replacement, the problem went away, but then came back 3 weeks later. The problem went away the very next day and the truck was fine for a week or so, then the problem came back so I had the sensor replaced hoping that this loss of engine reading would go away. A week later, the problem came back and then it went away and this has been going for months. The problem seems to have more and more often so I have been tracking this issue for the last four weeks and I can tell you the following for certain:

- The problem starts after 10-15 minutes of going on the freeway and the problem persists until I shut down the engine for a few hours, and then go back on the freeway.

This has been driving me insane because I have driven the truck for days in the city and the problem persists until I go to work and have to be on the freeway driving at 65 miles an hour. Once the problem goes away, it will not come back until I get on the freeway again. It doesn't always happen but for the past 6 days, it has been very consistent. I drive to work and before I get there, the fan is going full speed and I get no temp reading. Once I am on my way home, by the time I get off the freeway, the temperature reading is back and the engine works normally. I want to say it is probably a short somewhere but this consistent behavior is throwing me off. I have been hesitant to take the truck to the mechanic because I feel they are going to do some work, the problem will go away because somehow the problem gets resolved and then the problem comes back because what they did was not really the problem so I am hoping someone has had this problem and has a better insight. If I do ever find out what is wrong with mine, I will make sure to share it.
Thank you for reading.

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L8T BURB said:

I'll bet the house that a scanner will show you "coolant temperature below threshold". It will not illuminate the CEL, but even a cheap scanner from Harbor Freight will detect the stored code.

Rather than write a novel explaining my position on this, I'll save you the time of extensive reading and headache, and likely some money as well.

Replace the thermostat with a GM genuine thermostat. The coolant temp sensor is NOT the culprit. People get confused thinking it is, only to end up replacing it multiple times over and over before realizing the thermostat was the issue all along. Never once have I heard of someone replacing a thermostat with a GM genuine one, more than once.

Once you replace the thermostat, again... must use GM Genuine part, top off the coolant and clear any codes with cheap scanner. Guaranteed this will never happen again. I have gone through this issue myself, so I am speaking from experience and not theory. If you're unable or unwilling to source a scanner tool, removing the negative battery cable for a period of time may clear the code.

Please report back with your findings.

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