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

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How's the coolant level in the surge tank?

Any recent work done on the truck, like a new radiator?
 

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I would first replace the coolant sensor and make sure all connections are tight. If you're reading "0" that's the obvious place to begin. The sensor is below the thermostat housing and can be identified by its brass base that screws into the block. Replace it with battery disconnected, reconnect and see what happens. If that does not work, there is a separate pressure switch on the high side a/c line that forces the fans to run anytime the a/c is on high. Make sure the connections are tight. Its not a replicable item unless you 1st void the system of freon, replace then fill it back up. There is no reason for them to fail so check connections 1st.
wrong engine, on the l84/l86 it's on the waterpump just to the left of the thermostat housing, it's right in front of the engine
 
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I get it! I have decently strong Google-Fu. But there are times where I still get caught up not using the one magic keyword I need to pinpoint what I'm trying to find. I wasn't specifically looking for anything coolant temp sensor-related. I subscribe to LegitStreetCars and was catching up on the latest of his wife- I mean, the latest of his wife's supercharged Escalade. :p Your description of the symptoms reminded me of that video.




A stuck-open thermostat would still allow the coolant to warm up enough to register on the gauge and not just sit at "0". The PCM isn't seeing ANY temp at all, so it's playing it safe. It's far better for it to over-cool than under-cool.

I have actually watched the video from this guy when he first got hold of that ESV a year or so ago. He acquired it from the dealership near me for a song. I actually reached out to them saying if they had any other deals like that, count me in, as that was a steal.

As to the malady, I am confident the thermostat never was stuck in the closed position, as it never overheated. The fact it would go into that mode from a cold start also told me it was likely the sensor. Autozone said their scan tool said it was the thermostat code, but it is not as nuanced as the dealerships ability to differentiate.
A quick reset via disconnecting the battery has resolved the problem again, but I am not going to wait until the sensor goes out again.

I had the coolant flushed not too long ago, so I will not go through draining the system again (unless I cannot avoid it) just to change out the sensor.
 
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Vector

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How's the coolant level in the surge tank?

Any recent work done on the truck, like a new radiator?

Most recent work done was a new injector replacement, but nothing to do with the cooling system. The tank is at normal level.
 

Doubeleive

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I have actually watched the video from this guy when he first got hold of that ESV a year or so ago. He acquired it from the dealership near me for a song. I actually reached out to them saying if they had any other deals like that, count me in, as that was a steal.

As to the malady, I am confident the thermostat never was stuck in the closed position, as it never overheated. The fact it would go into that mode from a cold start also told me it was likely the sensor. Autozone said their scan tool said it was the thermostat code, but it is not as nuanced as the dealerships ability to differentiate.
A quick reset via disconnecting the battery has resolved the problem again, but I am not going to wait until the sensor goes out again.

I had the coolant flushed not too long ago, so I will not go through draining the system again (unless I cannot avoid it) just to change out the sensor.
You only have to drain enough coolant so that the level is just below full, or if you are quick you can just unscrew the sensor and stick one back in real quick you will loose a little coolant but not much unless you let it sit there and spew out.
 
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Vector

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You only have to drain enough coolant so that the level is just below full, or if you are quick you can just unscrew the sensor and stick one back in real quick you will loose a little coolant but not much unless you let it sit there and spew out.
That is what I assumed with a cold engine not under pressure. However my old mechanic skills do not always translate to modern engines/systems.
 

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We had the same problem on my wife's 2015 Tahoe a few months ago. I ended up replacing the thermostat sensor, which at first did not seem to fix the issue. Immediately after replacing the sensor, I cranked it up, let it run for a minute then turned it off. The fans continued to run at high speed just like before I replaced the sensor. On a whim I disconnected the batter for a few minutes in the hopes the system would reset itself when I reconnected it. Upon reconnecting the battery, the system operated as normal and it has been since then. I really don't know if the computer fixed itself with disconnecting the battery or if the sensor actually was bad, but either way it was fixed.

If you replace the sensor, just be quick like @Doubeleive said and you'll only lose a little bit of coolant. Make sure you let the engine cool down though so the coolant isn't too hot when it comes out.
 

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We had the same problem on my wife's 2015 Tahoe a few months ago. I ended up replacing the thermostat sensor, which at first did not seem to fix the issue. Immediately after replacing the sensor, I cranked it up, let it run for a minute then turned it off. The fans continued to run at high speed just like before I replaced the sensor. On a whim I disconnected the batter for a few minutes in the hopes the system would reset itself when I reconnected it. Upon reconnecting the battery, the system operated as normal and it has been since then. I really don't know if the computer fixed itself with disconnecting the battery or if the sensor actually was bad, but either way it was fixed.

If you replace the sensor, just be quick like @Doubeleive said and you'll only lose a little bit of coolant. Make sure you let the engine cool down though so the coolant isn't too hot when it comes out.
When you replace the coolant temperature sensor on these, the computer still treats the new one as suspect until it completes a new warm-up cycle and it sees that it's behaving within the range of normal parameters. Then the computer will reset the system and indications and fan behavior will return to normal. Disconnecting the battery will also reset the system but it shouldn't be necessary if you let it warm up fully.
 

BG1988

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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 touch, even the heat shield near the exhaust manifold barely felt hot.
I did not think much of it, then I received a message saying the A/C was shut down.
I got home, shut of the engine, but the fans were running at high speed and continued to do so, as if it was overheated, and needing additional cooling.

Being late at night, I didn't want the fans to drain the battery overnight, so I disconnected the battery. I called the dealership, and they said it sounded lie a sensor malfunction, or maybe the thermostat was stuck. For my Corvette, I know exactly where the temp sensor is, as well as the thermostat. On this behemoth, I have no clue where either are located.
In any event I decided to go out and examine the engine. Upon reconnecting the battery, and starting it up, everything seemed back to normal. A/C worked, fans on normal speed, and the coolant temp read a normal temp.

That was a couple of weeks ago, and I assumed the battery disconnect caused a re-boot if you will, and hoped the problem to just be an anomaly.
Sadly the problem started again with the exact same symptoms. This time I let the fans run after turning it off, and they ran for about 5 minutes, then shut off.
Now without a battery disconnect like last time, with a totally cold engine, if I start it up, the fans are going into high speed mode, despite the engine being totally cold. Thus I doubt the thermostat is getting stuck in the closed position, otherwise the engine would overheat.

So with all those symptoms being tied together, I am hoping others here have the knowledge of what it might be?
ECT sensor is not working most likely.. does it go to the normal range?
 

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