Engine Temperature Keeps Getting Lost and Fans Run at Full Speed

[Mistico3]

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.

 

[Fless]

I would recommend carefully inspecting the coolant temp sensor connector & pins for fitment, and for any compromised or broken wire in that harness near the connector. If anything there is questionable put a new pigtail on it.

I'd also replace the thermostat, as we've seen others here solve their similar issue with a new OE (make & temperature) thermostat.

 

[Joseph Garcia]

We need the underlying trouble codes that are generating this warning light on your dashboard.

I recommend that you get yourself a quality bi-directional scanner to add to your tool box. Then, you will be able to read ALL codes, along with a brief explanation/pointer to the source of your issue. You will literally save thousands of dollars in diagnostic and repair costs over the life of your truck, and you will most likely recoup the cost of the scanner within 1 year.

 

[Doubeleive]

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.

try the above suggestions but know that doing things like unplugging it and or disconnecting the battery sort of "resets" it for a few days and it may continue repeating the same issue.
if that happens source a new OEM temperature sensor from the dealer or from a local auto parts.
there is a bad rash of defective temp sensors and thermostats out there, this comes up ALL THE TIME now on here last post was just a week or so ago and a few days before that and a few day before that and so on, it has become a very common issue
some people have had to replace the sensor multiple times, as to if those are oem or not I do not know but I suspect not.

 

[Mistico3]

We need the underlying trouble codes that are generating this warning light on your dashboard.

I recommend that you get yourself a quality bi-directional scanner to add to your tool box. Then, you will be able to read ALL codes, along with a brief explanation/pointer to the source of your issue. You will literally save thousands of dollars in diagnostic and repair costs over the life of your truck, and you will most likely recoup the cost of the scanner within 1 year.

Hello Joseph,
Thank you for your response, the issue here is that there are no codes or light on my dashboard. The problem only lasts for either half a day to 2 days before it fixes itself for a day or two. Only once the issue lasted long enough for the Check Engine Light to come on but by the time I was going to take it to get a reading, the issue went away and the light went out and this has not happen again long enough for the light to come back on. I have actually been hoping that the problem shows up and does not go away so that I can take it to a mechanic.

 

[Mistico3]

try the above suggestions but know that doing things like unplugging it and or disconnecting the battery sort of "resets" it for a few days and it may continue repeating the same issue.
if that happens source a new OEM temperature sensor from the dealer or from a local auto parts.
there is a bad rash of defective temp sensors and thermostats out there, this comes up ALL THE TIME now on here last post was just a week or so ago and a few days before that and a few day before that and so on, it has become a very common issue
some people have had to replace the sensor multiple times, as to if those are oem or not I do not know but I suspect not.

Thank you for the information, I see that you are correct and there are a lot of posts here. Now that I know that this is common, I think I will see if I can get the wires to the sensor in case there is a problem with that which is causing this intermittent problem. If that does not solve the issue, then I will replace the thermostat just in case somehow that is related to this issue and will try a new sensor as well. I will keep everyone posted as to what I find and I appreciate all the help and suggestions everyone is leaving such as having to replace the sensor multiple times since that would not have been in my radar, or at least not for a while.

 

[Joseph Garcia]

Hello Joseph,
Thank you for your response, the issue here is that there are no codes or light on my dashboard. The problem only lasts for either half a day to 2 days before it fixes itself for a day or two. Only once the issue lasted long enough for the Check Engine Light to come on but by the time I was going to take it to get a reading, the issue went away and the light went out and this has not happen again long enough for the light to come back on. I have actually been hoping that the problem shows up and does not go away so that I can take it to a mechanic.

The code is stored in your truck's electronic system modules. To my knowledge, when a CEL appears on the dashboard, a trouble code is triggered, and it is stored (even though the CEL light on the dashboard disappears), and it does not reset or delete itself. Thus, with a quality bi-directional scanner, the trouble code can be retrieved and analyzed.