Fans running constantly

[RenegadePrue]

2018 Yukon Denali,
Driving the other day and the fans kick on and stay on. Also notice the temp gauge no longer shows a temp. So I went to the store and got the typical parts,
First, sensor replacement (no luck)
Back to store
Second, replace thermostat (no luck)
Third, fill system to make sure not air locked.
Replaces sensor second time thinking I got a bad sensor (no luck)
The heater blows hot but the one thing I am confused on is the upper radiator hose does not get hot. It is not air locked?!
What can it be??? I was thinking water pump is going out but the heater blows hot air so I don’t think it’s a water pump issue at all!!!
Please help with ideas!!!

 

[2016Dom]

Try disconnecting the battery for a bit, if you did not try that already.

 

[RenegadePrue]

Try disconnecting the battery for a bit, if you did not try that already.

Thank you, I did not try that one yet!!! Appreciate your response and help!

 

[Joseph Garcia]

Welcome to the Forum from NH.

Lots of knowledgeable folks here who freely share their knowledge, experiences, and perspectives. Knowledge is power.

I hope that you will become a participating member in the Forum's discussions.

Pics of the truck, please.

You are already receiving sage advice from the knowledgeable folks on this Forum.

 

[Geotrash]

2018 Yukon Denali,
Driving the other day and the fans kick on and stay on. Also notice the temp gauge no longer shows a temp. So I went to the store and got the typical parts,
First, sensor replacement (no luck)
Back to store
Second, replace thermostat (no luck)
Third, fill system to make sure not air locked.
Replaces sensor second time thinking I got a bad sensor (no luck)
The heater blows hot but the one thing I am confused on is the upper radiator hose does not get hot. It is not air locked?!
What can it be??? I was thinking water pump is going out but the heater blows hot air so I don’t think it’s a water pump issue at all!!!
Please help with ideas!!!

How many miles on it?

Those are the same symptoms as a stuck-open thermostat would have. It'll get warm enough to provide heat because coolant gets diverted to the heater core before it goes to the radiator, but the upper radiator hose remains cool-ish. And when the computer thinks the coolant temp should be higher than it is, it assumes the sensor has failed and turns the fans on as a precaution.

 

[RenegadePrue]

How many miles on it?

Those are the same symptoms as a stuck-open thermostat would have. It'll get warm enough to provide heat because coolant gets diverted to the heater core before it goes to the radiator, but the upper radiator hose remains cool-ish. And when the computer thinks the coolant temp should be higher than it is, it assumes the sensor has failed and turns the fans on as a precaution.

85k miles, the original thermostat worked when I put it in hot water, but I had replaced it already before checking it. So thermostat isn’t the issue. Also upper radiator hose isn’t getting hot at all….
GMC said it sounds like something major.

 

[Geotrash]

85k miles, the original thermostat worked when I put it in hot water, but I had replaced it already before checking it. So thermostat isn’t the issue. Also upper radiator hose isn’t getting hot at all….
GMC said it sounds like something major.

"Sounds like something major" = get ready to pay us big money to fix something you could fix at home for $25. In fact, an experience like that is why most of us are here.

The cooling system on these is simple. You could replace the radiator, every cooling line, the water pump and thermostat in a Saturday afternoon for less than $500. That said, we could also keep guessing or we could do some smarter troubleshooting. The fact that the upper radiator hose isn't getting hot would not be uncommon in colder temperatures. Where are you located?

I'm more concerned with why the fans are running at 100% duty cycle and why you're not getting a gauge reading on the dashboard. If the cause were mechanical, you would still be getting a temp gauge reading on the dash. With that, I believe the problem is still electrical. Did you also replace the pigtail on the coolant temp sensor? It's common for them to need replacing at the same time - so much so that many sensors include a new pigtail that you can splice in.

if you did replace the pigtail, do you have access to a bidirectional scanner? We need to know: coolant temp as the computer sees it, and what the computer is commanding the fans to do. We also need to know if there are any other codes set. The shop manual (alldata) has a troubleshooting chart that explains what different parameters will trigger the fans to 100% duty cycle. Troubleshooting starts with this:

Circuit/System Verification​

1. Ignition ON.
2. Verify that DTC P0480, P0691, or P0692, is not set.
   • If a DTC is set
     Refer to DTC P0480, P0691, or P0692.
   • If no DTC is set.
3. Verify the scan tool Cooling Fan Motor Command parameter is 0 %.
   • If greater than 0 %
     Refer to Diagnostic Aids and Symptoms - Engine Cooling for further diagnosis.
   • If 0 %
4. Verify that the G10 Cooling Fan Motors are not operating.
   • If a G10 Cooling Fan Motor is operating
     Test or replace the appropriate G10 Cooling Fan Motor.
   • If the G10 Cooling Fan Motor is not operating
5. All OK.

If P0480, P0691, or P0692 are present, then:​

Circuit/System Description​

The engine control module (ECM) commands the speed of the cooling fans based on cooling requirements. The ECM controls the cooling fan speed by commanding the cooling control module. The cooling fan control module supplies separate power and ground circuits for each cooling fan. The ECM sends a pulse width modulated (PWM) signal to the cooling fan control module. The cooling fan control module interprets the signal and operates the cooling fans at the commanded speeds.

Conditions for Running the DTC​

• The ignition voltage is 11 volts or greater.
• The engine speed is 400 RPM or greater.
• The ECM driver transitions from ON to OFF or from OFF to ON.
• DTCs P0480, P0691, and P0692 run continuously once the above conditions are met.

Conditions for Setting the DTC​

The ECM detects that the commanded state of the driver and the actual state of the control circuit do not match for greater than 5 seconds.

Action Taken When the DTC Sets​

• DTCs P0480, P0691, and P0692 are Type B DTCs.

Conditions for Clearing the MIL/DTC​

• DTCs P0480, P0691, and P0692 are Type B DTCs.

Diagnostic Aids​

• A delay or ramp up of approximately 12 seconds may occur before the cooling fan activates or changes speed when being commanded with a scan tool.

 

[RenegadePrue]

"Sounds like something major" = get ready to pay us big money to fix something you could fix at home for $25. In fact, an experience like that is why most of us are here.

The cooling system on these is simple. You could replace the radiator, every cooling line, the water pump and thermostat in a Saturday afternoon for less than $500. That said, we could also keep guessing or we could do some smarter troubleshooting. The fact that the upper radiator hose isn't getting hot would not be uncommon in colder temperatures. Where are you located?

I'm more concerned with why the fans are running at 100% duty cycle and why you're not getting a gauge reading on the dashboard. If the cause were mechanical, you would still be getting a temp gauge reading on the dash. With that, I believe the problem is still electrical. Did you also replace the pigtail on the coolant temp sensor? It's common for them to need replacing at the same time - so much so that many sensors include a new pigtail that you can splice in.

if you did replace the pigtail, do you have access to a bidirectional scanner? We need to know: coolant temp as the computer sees it, and what the computer is commanding the fans to do. We also need to know if there are any other codes set. The shop manual (alldata) has a troubleshooting chart that explains what different parameters will trigger the fans to 100% duty cycle. Troubleshooting starts with this:

Circuit/System Verification​

1. Ignition ON.
2. Verify that DTC P0480, P0691, or P0692, is not set.
   • If a DTC is set
     Refer to DTC P0480, P0691, or P0692.
   • If no DTC is set.
3. Verify the scan tool Cooling Fan Motor Command parameter is 0 %.
   • If greater than 0 %
     Refer to Diagnostic Aids and Symptoms - Engine Cooling for further diagnosis.
   • If 0 %
4. Verify that the G10 Cooling Fan Motors are not operating.
   • If a G10 Cooling Fan Motor is operating
     Test or replace the appropriate G10 Cooling Fan Motor.
   • If the G10 Cooling Fan Motor is not operating
5. All OK.

If P0480, P0691, or P0692 are present, then:​

Circuit/System Description​

The engine control module (ECM) commands the speed of the cooling fans based on cooling requirements. The ECM controls the cooling fan speed by commanding the cooling control module. The cooling fan control module supplies separate power and ground circuits for each cooling fan. The ECM sends a pulse width modulated (PWM) signal to the cooling fan control module. The cooling fan control module interprets the signal and operates the cooling fans at the commanded speeds.

Conditions for Running the DTC​

• The ignition voltage is 11 volts or greater.
• The engine speed is 400 RPM or greater.
• The ECM driver transitions from ON to OFF or from OFF to ON.
• DTCs P0480, P0691, and P0692 run continuously once the above conditions are met.

Conditions for Setting the DTC​

The ECM detects that the commanded state of the driver and the actual state of the control circuit do not match for greater than 5 seconds.

Action Taken When the DTC Sets​

• DTCs P0480, P0691, and P0692 are Type B DTCs.

Conditions for Clearing the MIL/DTC​

• DTCs P0480, P0691, and P0692 are Type B DTCs.

Diagnostic Aids​

• A delay or ramp up of approximately 12 seconds may occur before the cooling fan activates or changes speed when being commanded with a scan tool.

The only good thing is we just bought this two months ago and opted for the exclusionary bumper to bumper warranty. So we do have full coverage warranty so it will only cost me $100 deductible. Not sure if this helps at all but another issue when it’s in park and you floor it at 2500 rpm it stalls or more of a hiccup on the rev.
I’m in Washington state and yes it’s cold, but after driving for an hour yesterday the upper radiator was still not hot?! Is this normal for these not to get hot?
And last, I will go get a live read obd2 today as I just got an old basic obd2 scanner and it would not communicate with the car for some reason?!?!
Thanks for all the info!!
You are the best!

 

[Jimmy17]

Thank you, I did not try that one yet!!! Appreciate your response and help!

So? I'm experiencing the same symptoms. I pulled the 40A fuses for both fans so as to not drain the battery (I hate it when that happens) once I have parked the vehicle and turned off the ignition. The engine is not hot, therefore. what is causing the fans to kick on and stay on? Did the suggested cure of disconnecting the battery have any effect?

 

[2016Dom]

When it happed to me i chained the thermostat and temp sensor, dis connected the battery while working on it.
Short trips Yukon never got up to temp, ether a bad thermostat or temp sensor.
Read some place that when the ECM goes into some sort of safety mode when temp readings are not what is expected the fans come on thinking the engine could be over heating.

 

[Fless]

So? I'm experiencing the same symptoms. I pulled the 40A fuses for both fans so as to not drain the battery (I hate it when that happens) once I have parked the vehicle and turned off the ignition. The engine is not hot, therefore. what is causing the fans to kick on and stay on? Did the suggested cure of disconnecting the battery have any effect?

It would help to know what you're working on. Consider adding some vehicle info to your signature so it's always there for reference and context.

Are there any DTCs set? If so, which ones?

Does the ECT gauge work? Does it agree with what a scan tool shows as the coolant temp?

 

[joe_joe]

I had this happen on my 2015 Suburban and it was the temperature sensor that went bad.

I started with pulling the battery cables and while this ended up resetting it, once I started driving again the fans went right back to full blast.

I reached out to a mechanic buddy and he said it was the temp sensor and lucky for me he was right. Easy fix in the driveway.

 

[OR VietVet]

I just did this repair on my landlord's 2018 Suburban with a 5.3. The fans were stuck on very high speed and he let it run long enough that it caused some bearing noise and I ended up replacing the fans and shroud. The CTS looked like this and the temp gauge was stuck at 160 degrees and the thermostat was suspect. I changed them and had the battery disconnected during the process. He was still getting heat. The system was keeping fans on, even after ignition was shut off. He pulled the 40 amp fuse to shut them down. This is a well documented problem at you tube. The bearings were worn bad enough, that when they were cycled off and then would do a restart, there was a chirp noise from the bearing area but no noise when running. I used Genuine GM parts for CTS and thermostat assembly.

 

[Vector]

I experienced the same problem, and this thread might be helpful;

Fans run like the engine is overheating, coolant gauge reads no temperature, A/C disengaged.

My 2015 Escalade was running fine, but I noticed a loud hum under the hood. The fans were running much faster than usual, so I looked at my coolant guage and it was reading zero, despite me having driven for miles. I pulled over and under the hood the temp felt fine, hose barely warm to the...

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