2017 1500 Sierra cooling fan on constantly and no temp reading on gauge

ChevyGMCfan · January 19

Hello: the cooling fan came on this morning with a cold engine, and the temp gauge did not indicate any temperature as the truck was driven. The fan stayed on for several minutes after shutdown. I couldn't find a thread related to this. Anyone have any experience with this? 2017 1500 Denali with 5.3, 4WD.

Note: my wife's 2017 Acadia Denali V6 did the same thing, I replaced the temp sensor and thermostat, problem solved. Coincidence?

PFTX_5.3 · January 19

I had the same problem. I only replaced the thermostat, and that fixed the issue. The correct fix is to replace the thermostat and temp sensor.

mikeyk101 · January 20

Just to add, I highly recommend using an OEM thermostat if you are going to replace it. I have a 2016 and back in early 2023, that original thermostat was getting stuck open and my truck struggled to warm up and get heat to the cabin. I went with a Motorrad 194⁰ aftermarket thermostat and very quickly, that one failed and was getting stuck partially closed so the truck would occasionally run hotter than it was supposed to. I ended up replacing it with the OEM 194⁰ thermostat that I believe is used in the Cadillac CTS 6.2l as well as other motors like for Corvettes and Camaros. Part number is # 12674634 but is also listed as 15-11113. The OEM for my 5.3l was a 207⁰ thermostat and I wanted a little buffer for when I tow my toy hauler or cargo trailer. So far I have not had any issues. I also wanted to go back to OEM because I figured if the original one ran fine for almost 7 years, another OEM will give me the same or hopefully better. The Motorrad was a complete waste of money.

Now during all this, I never noticed an issue with fans running more than they should or the coolant gauge reading 0 so you may also need to replace the temp sensor like you mentioned and @PFTX_5.3 also mentions.

Edited January 20 by mikeyk101

newdude · January 20

Thermostat. Go OEM. You can replace the temp sensor if you want to as well as its right there.

ChevyGMCfan · January 20

Thanks, guys. This confirms my thoughts.

B.Sharp · March 6

OK, I’m having the same issue and it’s driving me crazy.

First I replaced the temp sensor with a Standard brand unit. That fixed it for a couple of weeks, then the problem came back. The fan started running constantly again.

At that point I thought it might be the thermostat, so I replaced that. Same story. It worked for a few weeks, then the fan started running all the time again.

Next I installed a factory temp sensor. So now the truck has a factory thermostat and a factory temp sensor. That worked for about three or four weeks, then the problem returned.

At this point, about every three weeks I stop by a friend’s shop and he clears the code. Everything goes back to normal for a while, then the issue comes back.

The truck is a 2014 SLE 4x4 Crew Cab with the 5.3. It has almost 130K miles. I bought it new and have had zero issues with it until the last four months. This temperature issue is just ridiculous.

I’m wondering if something else could be causing it. It feels like it might be electrical. Every once in a while I also get a “Service Charging System” message.

The alternator did fail on me while I was driving on the highway, so I had to get it towed. I replaced it with a factory unit. Most of the time the gauge shows around 14 volts, but occasionally it will drop to 12 while I’m driving. If I stop, turn the truck off, and restart it, it goes back to 14 and stays there.

It’s very intermittent. I’m starting to wonder if the charging system issue and the temperature issue could be related.

Edited March 6 by B.Sharp

MikeBMW · March 11

On 3/6/2026 at 1:27 PM, B.Sharp said:

Most of the time the gauge shows around 14 volts, but occasionally it will drop to 12 while I’m driving. If I stop, turn the truck off, and restart it, it goes back to 14 and stays there.

The alternator is checked by the BCM (maybe ECM?) and will change depending on the battery level.
It's not unusual to see a variation from 12 volts to 14 volts.
If you had a battery change, assure the charging ring is still in place.