Cooling Fans Running - Temperature Gauge not working - my data, experience and rigged fix.

[The guitar zombie]

I am starting this thread because you have to go through a lot of posts to get where I am.

The problems (many models have it):


1) My 2015 Yukon Denali’s engine temperature gauge intermittently reads zero and the cooling fans come on where the computer assumes the sensor has failed so the car goes into a protective safe mode (fans run constantly - better too cool than too hot). if the Car is shut off with the fans running, they start up again when the car starts and will continue to run until 5 minutes after the car shuts off. The fans may, or may not start up the next time the car is started. It may run for a day or two and the problem will start up again.

2) The running fans cause problems.

a) the battery gets drained. On my Yukon, a near dead battery does not act typical to other older cars. Lights are bright, they don’t dim when heater is turned on, but when you hit the start button, the dash display goes black. Then the dash lights and headlights are bright again. Don’t be decieved, this is how a dead battery works (or doesn’t work) in a GM.

b) Because the control module doesn’t know the engine temp, the engine may not run properly. It may run rough or may be harder to start. Exhaust may be a bit more smelly.


Troubleshooting: I had my mechanic replace the engine temperature sensor. It worked, not because it needed one, but because he disconnected the battery and reconnected it. I took the old one and tested it. When the “old” sensor was immersed in three different cups of water (room temp 70°, ice cold 35° and hot 130° I measured the sensor’s resistance each time. It worked within spec (chart can be found on line). So my sensor wasn’t bad.

Opinions: many opinions and theories were offered in previous posts.

1. The sensor itself is cheap and therefore intermittent. I am an engineering specialist with expertise in instrumentation and sensors. No. Not in this case.
2. The wiring caused a power surge and killed the sensor. Again, no.
3. One post even replaced the car’s computer ($$$) and still did not solve the problem.
4. Loose connectors. I can’t say 100% no, but my mechanic did check the sensor’s connector.

Solution: This works but is not really a solution, but a work around. I added a battery switch. When I shut the car off, if the fan is running, I kill the battery via the switch (I bought and installed - there are many configurations). Every time, so far, the car starts normal (no fan running). There are systems you can buy that provide a switch near the dash. The cutoff can be an added safety feature as well. But, you will have to reset your date and time. Some of the car’s personal settings will have to be reprogrammed. The radio stations remain programmed though.

Suspicions: I think it is a control module programming issue.

Other thoughts - maybe rigging the control module fuse to have an in line switch on one of the terminals will reset the problem. I don’t know (yet) but next time, instead of disconnecting the battery, I will pull the fuse to see if it resets the temp sensing system. My guess is that it has the same effect (reprogramming) as disconnecting the battery cable, if it does the reset.

I will edit this post as I try different things.

 

[mattbta]

The emissions monitors are going to be a PITA to complete if you have to get an obdii state inspection if you’re killing the battery every shutoff.

 

[Fless]

Have you thought about reading the ECT sensor temp with a scanner to see what it's reporting? Then comparing that to actual (give or take) with an infrared temp gun?

 

[HouTexTruckGuy]

I had the same problem with the Temp gauge stuck on zero and fans running, and no AC.

I changed out the ECT and it seems to have fix the problem and then it re-occured about a week later. I then used an OBD code reader and got the P0128 (Coolent Temperature Below Thermostat Regulating Temperature). I then used the OBD reader and erased the P0128 code reading. Everything went back to normal. We'll see if it lasts before troubleshooting further. I'm keeping the OBD reader in the vehicle because if the fan stays on too long, I check the see if the code is present. Erasing the code shuts the fans off immediately when the engine is not running.

 

[Geotrash]

I had the same problem with the Temp gauge stuck on zero and fans running, and no AC.

I changed out the ECT and it seems to have fix the problem and then it re-occured about a week later. I then used an OBD code reader and got the P0128 (Coolent Temperature Below Thermostat Regulating Temperature). I then used the OBD reader and erased the P0128 code reading. Everything went back to normal. We'll see if it lasts before troubleshooting further. I'm keeping the OBD reader in the vehicle because if the fan stays on too long, I check the see if the code is present. Erasing the code shuts the fans off immediately when the engine is not running.

Boom! Guy stops in for one post and it's a winner!

 

[L8T BURB]

Sorry to bump an old post, but I have the fix for this!!

I had this EXACT problem with my 2015 Suburban, and after extensive research online I realized there is not a lot of GOOD information on a true root cause/fix. I will include details of my repair journey which ultimately led me to the solution....

1. Replaced coolant temp sensor w/Autozone sensor (Temporarily seemed to correct the issue)
2. Replaced coolant temp sensor a 2nd time (Autozone warranty)
3. Replaced thermostat AND coolant temp sensor w/genuine GM parts (FIXED)

The only thing I can figure is that the factory thermostat was worn out and was leaking off (constantly staying partially open). This caused the engine temp to never get to normal operating range. This causes the vehicle to enter a "fail safe" mode, causing the fan to run non-stop (including several minutes after shut off), and also causes your AC system to not allow the AC compressor to engage.

If you run the engine long enough like this, you'll eventually get a check engine light and the code will read "operating temp below threshold". This means the engine is unable to get to normal operating range, and is fully entering the fail safe mode.

Trust me...I know it sounds far fetched to believe all these systems are tied together....but I assure you they are.

In short, grab a genuine GM thermostat housing as well as a genuine GM coolant temp sensor. You'll also need about a gallon of Dex-Cool. This repair is quick and easily can be done in your garage/driveway within 30 minutes with a couple of simple hand tools.

Hope this helps!!

 

[zcb350fb]

hey interceptor589. do you have part numbers for those parts? I ran into this issue two days ago. replaced temperature sensor in auto zone parking lot because we were traveling. car ran great fro two days on the brand new sensor and then the issue resurfaced again today

 

[Thrust]

This is common on Cadillac CT6 3.0TT engines as well. Same fix, thermostat and temp sensor.

 

[Fless]

hey interceptor589. do you have part numbers for those parts? I ran into this issue two days ago. replaced temperature sensor in auto zone parking lot because we were traveling. car ran great fro two days on the brand new sensor and then the issue resurfaced again today

TIP o' the day: if you want to "tag" someone so they get notified, use either the "Reply" feature at the bottom of his/her post (like I did above), or start with the "@" sign, then start to type the username. A dropdown list will appear.

Like this:

Select the username from the dropdown -- @zcb350fb -- and continue writing your message. If you don't use either of those methods your target might not see your question.

 

[03catburban]

If temp sensor is reading correctly then it's always the thermostat that causes that issue, I've repaired many GM models for this exact same issue

 

[L8T BURB]

hey interceptor589. do you have part numbers for those parts? I ran into this issue two days ago. replaced temperature sensor in auto zone parking lot because we were traveling. car ran great fro two days on the brand new sensor and then the issue resurfaced again today

@zcb350fb These are the part numbers that I used. YMMV.

12608814 - Coolant Temp Sensor ~$30
12674639 - Outlet Assembly w/Thermostat ~$50

You'll also need about a gallon of Dexcool, as you'll lose some when replacing the sensor and thermostat.

Clearing the code with a pocket scanner will temporarily cure the problem, but it will only continue happening until this repair is made. If you have a pocket scanner, it may not be a bad idea to keep it in your vehicle until you're able to do the repair. I noticed that when my engine light came on before the repair, I could simply pull off the road, clear the code, and systems would temporarily resume as normal.

 

[Terry2015Tahoe]

Boom! Guy stops in for one post and it's a winner!

Hi Grady,
I had the same issue and I noticed that temperature was running "low" after clearing the code. The problem was a stuck thermostat. Took me less than an hour to install new one and all issues are resolved. I made a quick video on steps.....Hope this helps.

 

[sandyjk]

We are in the midst of fixing this. Replace the coolant temperature gauge and the thermostat, then disconnect the battery for a minute or so. Reconnect and you should be good to go. We replaced the coolant temp gauge twice and the fan behaved for a few days, and then it would blow again, no engine temp registered, and it would continue blowing for six minutes when I'd shut off the engine. Apparently the underlying issue is that the thermostat gets air in it and stops working. There are youtube tutorials on how to replace both items.

 

[Fless]

Replace the coolant temperature gauge ...

Do you mean the coolant temp SENSOR?

 

[hatinthering]

I had exactly the same symptoms (15 Tahoe). Replaced temp sensor, but problem resurfaced a couple weeks later.

The permanent fix was a new thermostat....didn't realize until replacing that I was never really coming up to full temp (gauge straight up), it had always been running on the cool side of normal. Probably confused the computer and threw into default mode of fans on and '0' temp gauge.

Zero issues after replacing thermostat, and gauge points straight up now.

 

[Krbobby]

So I just replaced the coolant temp sensor, for the third time, now did the thermostat with it. As soon as I start the car now, the fan instantly goes into the constant on mode. What went wrong?

 

[Bagherra]

So I just replaced the coolant temp sensor, for the third time, now did the thermostat with it. As soon as I start the car now, the fan instantly goes into the constant on mode. What went wrong?

Did you clear codes? From what i've heard, you might not get a CEL but the code will be stored...

 

[Krbobby]

It’s never thrown a code for the situation. However, I unplugged the coolant temp sensor and had a bent pin inside that I couldn’t see in the dark.
Straighten the pin, plugged it back on and everything is great.
Thanks for your response!!

 

[Bagherra]

When replacing the thermostat or ECT, and there is air trapped in coolant system, how do you "burp" it?

 

[Krbobby]

All I did was open the reservoir and ran it till it got hot and then added a little more coolant. Put the lid on it continued to run it. I had zero problems after that. Right or wrong, idk, worked for me.