Temp gauge quit working, and engine fans running needlessly.

fishnaked · March 15

Hi,

I have a 2015 Sierra truck with ~130k. Today, two things happened. 1) The temp gauge stopped working 2) The engine fans come on after I shut the engine off and remain on for 3-4 minutes. It's only 50 degrees outside. I've never heard these fans come on in the heat of the summer.

I assume these two things are somehow related, being they both started occurring at the same time.

The heater works as it always has. It puts out heat...but not as much as other vehicles I have owned.

Any ideas what is going on?

Thanks.

CamGTP · March 15

Bad coolant temp sensor.

JimCost2014 · March 15

1 hour ago, fishnaked said:

Hi,

I have a 2015 Sierra truck with ~130k. Today, two things happened. 1) The temp gauge stopped working 2) The engine fans come on after I shut the engine off and remain on for 3-4 minutes. It's only 50 degrees outside. I've never heard these fans come on in the heat of the summer.

I assume these two things are somehow related, being they both started occurring at the same time.

The heater works as it always has. It puts out heat...but not as much as other vehicles I have owned.

Any ideas what is going on?

Thanks.

If you have never changed your thermostat, replace it with an OEM version, best place to start.

mikeyk101 · March 15

When the thermostat on my 2016 failed 3 years ago and was sticking open, I noticed that the temp gauge would not go all the way to the 210 mark in the winter and although there was some heat, it wasn't what it should be. I first replaced it with a Motorrad aftermarket thermostat and within months, that failed and want opening all the way. I switched to a GM thermostat and haven't had any trouble since. So I agree with the above posted comment by @JimCost2014. But I also went with a 194⁰ GM thermostat instead of the stock 207⁰ one because I do occasionally tow and wanted to give the system to start getting the benefits of the radiator sooner. But if your temp gauge isn't moving at all then @CamGTP has the answer you need.

Eric G · May 9

So I just had this issue. Fans on High, no movement of the temp gauge on the dash. Replaced Coolant Temp Sensor, no change. Replaced thermostat, no change. Interesting note; the engine temp could be read via data stream on the code reader, but the needle on the dash gauge never moved. Checked with code reader again, P0128 as expected. Attempted to clear codes and noticed that my scan tool read "erase command rejected". I have never seen a request rejected before. Went with the sure fire way to clear codes, disconnect the negative battery cable, wait, then reconnect. Verified that no codes were present with one more read before starting up. Everything worked after the hard reset. Temp gauge worked and agreed with what I was seeing on the scan tool and the fans were not running any more. Be sure to clear your fault codes to make the sensor/thermostat fix actually work.

asilverblazer · May 11

On 5/9/2026 at 3:48 PM, Eric G said:

So I just had this issue. Fans on High, no movement of the temp gauge on the dash. Replaced Coolant Temp Sensor, no change. Replaced thermostat, no change. Interesting note; the engine temp could be read via data stream on the code reader, but the needle on the dash gauge never moved. Checked with code reader again, P0128 as expected. Attempted to clear codes and noticed that my scan tool read "erase command rejected". I have never seen a request rejected before. Went with the sure fire way to clear codes, disconnect the negative battery cable, wait, then reconnect. Verified that no codes were present with one more read before starting up. Everything worked after the hard reset. Temp gauge worked and agreed with what I was seeing on the scan tool and the fans were not running any more. Be sure to clear your fault codes to make the sensor/thermostat fix actually work.

Just did this on my 2016 Yukon Denali, I had to disconnect the battery to reset it as well. I didn't replace the thermostat - just the sensor.

Northside · May 18

I had this happen to my '14 Silverado with 89000 miles on it a couple of weeks ago. I shut it off in my garage, but the fans kept running, so I undid the negative battery cable and the fans stopped. I watched a few YouTube videos which recommended changing both the thermostat and temperature sensor. I thought about doing the job myself, but I was sitting my granddaughter who couldn't walk due to an ankle injury. A local shop wanted nearly $800 to do the job. That sounded ridiculous so I followed the videos and did it myself in just an hour with cleaning up and wiping down the tools. I did disconnect the battery's negative cable before starting the job. The truck runs perfectly now!