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Radiator fans are not working properly, they only turn on with the A/C on?

Tiny
GM1321
  • MEMBER
  • 2007 GMC SIERRA
  • 4.8L
  • V8
  • 2WD
  • AUTOMATIC
  • 98,000 MILES
The engine overheats without the A/C on, and the fans never turn on. I have replaced the water pump and thermostat, engine temperature sensor, the relays, checked the fuses, and put in a new ECM and nothing has resolved the issue yet. What else could be the problem? Thanks.
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Saturday, August 6th, 2022 AT 9:27 AM

8 Replies

Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
  • 43,110 POSTS
It looks like there are four relays that run the system. Did you replace all of them? Also, there are two fans, do both work? Here are the wiring diagrams for the fans so you can see how the system works and a guide to help you test the connections:

https://www.2carpros.com/articles/how-to-check-wiring

Can we see if there is power for the fan1 and fan2 fuses? This guide can help:

https://www.2carpros.com/articles/how-to-check-a-car-fuse

Here are the fuse locations as well. Check out the diagrams (below). Please let us know what you find. We are interested to see what it is.
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Sunday, August 7th, 2022 AT 8:37 AM
Tiny
GM1321
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  • 5 POSTS
I replaced all relays. Both fans work when the A/C is turned on. I checked all of the fuses, and none looked bad.
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Sunday, August 7th, 2022 AT 4:01 PM
Tiny
KEN L
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  • 43,110 POSTS
Lets check the ground at the lower radiator support, see if it is loose or corroded.
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Monday, August 8th, 2022 AT 5:37 PM
Tiny
GM1321
  • MEMBER
  • 5 POSTS
I’m not sure if I checked the right grounds or not. I checked the grounds on the driver side and passenger that are underneath the radiator that are connected to the frame of the truck. Both are tight and not corroded. The head of the bolt on the passenger side had a couple little small spots of rust but the ground wire connection was clean. The picture is of the ground I checked on the driver side. Not sure if it will help you know if I checked the right ground or not.
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Tuesday, August 9th, 2022 AT 7:07 PM
Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
  • 43,110 POSTS
Yep, it looks good, we need to check the system for broken wires, use the wiring diagrams above and this guide to confirm the connections. There are only relays, coolant sensor and the PCM in the system. Have you run the codes? Also, what makes you say the engine is overheating?

https://www.2carpros.com/articles/how-to-check-wiring

and

https://www.2carpros.com/articles/checking-a-service-engine-soon-or-check-engine-light-on-or-flashing

Please run down this guide and report back.
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Wednesday, August 10th, 2022 AT 12:31 PM
Tiny
GM1321
  • MEMBER
  • 5 POSTS
No codes are present. The engine temp keeps climbing without the A/C running and the fans never engage. I haven’t ever let it get higher than 230 while idling but the fans never come on. It runs at 210 with the AC on and the fans running. Electrical isn’t my thing but it sounds like that is what we have narrowed it down to so I will give it a look based on the diagrams etc. You provided.
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Thursday, August 11th, 2022 AT 2:11 PM
Tiny
GM1321
  • MEMBER
  • 5 POSTS
The ground to the hood had essentially an inch of play in that ground wouldn’t have anything to do with my problem, right? Does it matter which direction the relays are installed in? Looks like none of them are the same on my other two cars that work fine so I assume it doesn’t matter. Thanks.
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Friday, August 12th, 2022 AT 9:43 AM
Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
  • 43,110 POSTS
Yep, that can be a problem the direction the relay is in can matter even though it can go in both ways, I am not happy about that from GM. Try switching the relay orientation to see if it changes. Thanks for getting back to me.
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Friday, August 12th, 2022 AT 11:49 AM

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