Fans always run!

Tiny
SHADOWEN1
  • MEMBER
  • 2007 CHEVROLET SILVERADO
Engine Cooling problem V8 Four Wheel Drive Automatic 14500 miles

I have an 07 silverado classic with OEM electric cooling fans. The fans run constantly. As soon as the engine starts the fans come on and run on low for about 5 seconds and then kick up to high until I shut off the engine. I have replaced the coolant temp sensor, the relays in the aux fuse box and checked the radiator sensors which seem to be good. I checked the wiring and it all looks good. I am at a loss. What else could it be.

When you first start the engine both fans come on at low speed for about 5 seconds and then both go up to high speed until you turn the truck off. I have replaced all three relays and no dice. I have looked for a short or spliced wire but have not found any. That is why I am so stumped on this.
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Wednesday, December 17th, 2008 AT 3:57 PM

10 Replies

Tiny
BRIAN 1
  • EXPERT
The only other thing I can suggest is did you scan for any dtc's, there could also be a trouble code. Coolant fan problems might not turn on the SES light but there could be a dtc. Also looking at the scematic there could also be a problem in the pcm because there are 2 drivers in the pcm which are relay control grounds. The pcm controls the relays. (This is just a suggestion) but there could even be a problem in the pcm. You need to use a scan tool that is able to command the fans on and off. This might help to diagnose it. Post back with other questions/answers.
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Wednesday, December 17th, 2008 AT 5:27 PM
Tiny
SHADOWEN1
  • MEMBER
Yes I hookd up my ODB2 scan tool but received no DTC's. But my tool can't sent a commant to shut off the fans. Is there any other way to check the PCM?
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Wednesday, December 17th, 2008 AT 6:14 PM
Tiny
SHADOWEN1
  • MEMBER
I was thinking maybe if it could be a problem with the override relay for the A/C? I don't actually know if this truck has this but I know most aftermarket fan controlers have another switch that turns the fans on if the A/C is turned on. If that switch went bad could that be the cause of this? I don't know where this would be located at so this is someting I have never checked.
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Wednesday, December 17th, 2008 AT 6:26 PM
Tiny
BRIAN 1
  • EXPERT
Only other thing I could think of, is the coolant low or does the coolant sys have air in it, that could cause the fans to run on high.I looked at the scematic and the diagnostic it's preety straight forward, it just says to check all relays and check for a short to voltage on the motor supply voltage circuit. I also found this info on the operation of the fans, this might help. The engine cooling fan system consists of 2 electrical cooling fans and 3 fan relays. The relays are arranged in a series/parallel configuration that allows the powertrain control module (PCM) to operate both fans together at low or high speeds. The cooling fans and fan relays receive battery positive voltage from the underhood fuse block.

During low speed operation, the PCM supplies the ground path for the low speed fan relay through the low speed cooling fan relay control circuit. This energizes the low speed fan relay coil, closes the relay contacts, and supplies battery positive voltage from the low fan fuse through the cooling fan motor supply voltage circuit to the left cooling fan. The ground path for the left cooling fan is through the cooling fan s/p relay and the right cooling fan. The result is a series circuit with both fans running at low speed.

During high speed operation the PCM supplies the ground path for the low speed fan relay through the low speed cooling fan relay control circuit. After a 3 second delay, the PCM supplies a ground path for the high speed fan relay and the cooling fan s/p relay through the high speed cooling fan relay control circuit. This energizes the cooling fan s/p relay coil, closes the relay contacts, and provides a ground path for the left cooling fan. At the same time the high speed fan relay coil is energized closing the relay contacts and provides battery positive voltage from the high fan fuse on the cooling fan motor supply voltage circuit to the right cooling fan. During high speed fan operation, both engine cooling fans have there own ground path. The result is a parallel circuit with both fans running at high speed.

Important: The right and left cooling fan connectors are interchangeable. When servicing the fans be sure that the connectors are plugged into the correct fan.

The PCM commands the low speed cooling fans ON under the following conditions:

" Engine coolant temperature exceeds approximately 104.25 C (220 F).

" A/C refrigerant pressure exceeds 1447 kPa (210 psi).

" After the vehicle is shut OFF if the engine coolant temperature at key-off is greater than 101 C (214 F) the low speed fans will run for a minimum of 60 seconds After 60 seconds, if the coolant temperature drops below 101 C (214 F) the fans will shut OFF. The fans will automatically shut OFF after 3 min. Regardless of coolant temperature.

The PCM commands the high speed fans ON under the following conditions:

" Engine coolant temperature exceeds approximately 107.2 C (225 F).

" A/C refrigerant pressure exceeds approximately 1824 kPa (265 psi).

" When certain DTCs set.

At idle and very low vehicle speeds the cooling fans are only allowed to increase in speed if required. This insures idle stability by preventing the fans from cycling between high and low speed. I do't know to many more suggestions, I hope some of this info helped. If you get stuck of find any other info post back.
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Wednesday, December 17th, 2008 AT 10:30 PM
Tiny
SHADOWEN1
  • MEMBER
I will do some more trouble shooting. Thanks for all your time and all the info. You gave me a lot more help than I have been able to get anywhere else. I really appreciate it.
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Wednesday, December 17th, 2008 AT 10:56 PM
Tiny
JEEVES1169
  • MEMBER
I have the same problem with my 2007, did you ever find out what was wrong?
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Thursday, July 26th, 2012 AT 8:14 AM
Tiny
DJCL
  • EXPERT
A quick thing to check is un plug the ecm connecters and check inside for green powder. This truck was known to have problems with the plug letting water get in and fans running all the time. Clean out the plug end and the ecm end.
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Thursday, July 26th, 2012 AT 1:26 PM
Tiny
AARONPHILLIPS81
  • MEMBER
Resurecting an old thread.
I have the same issue and can't pinpoint what it is. Engine temp on dash never reads higher than before. Trans temp is steady around 150. Even with the a/c off the fans will run almost immediately after startup.
Next step is to change coolant temp sensor? Anyone know where it's located?
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Monday, March 28th, 2016 AT 5:59 AM
Tiny
PLATINUMWEDDINGS
  • MEMBER
Hello, Im having the same problem. 2007 chevy tahoe. 5.3. Fans going right to high and wont turn off till the cars off. What was the out come of your problem?
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Saturday, May 14th, 2016 AT 4:25 PM
Tiny
KEN
  • ADMIN
Hello,

I have found that if the ac system has too much Freon in it the computer thinks the system is overheating and runs the fans on high to try and cool the condenser. Please check the state of charge and get back to me.

https://www.2carpros.com/articles/re-charge-an-air-conditioner-system

and

https://www.2carpros.com/articles/air-conditioner-how-to-add-freon

Here is the air conditioner wiring diagrams (below) so you can see what I'm talking about.

Please let us know what happens, we are interested to see what it is.

Cheers, Ken
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Monday, June 26th, 2017 AT 9:55 PM

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