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Engine overheats but the cooling fans do not turn on unless the AC comes on

Tiny
BRANDON STORCH
  • MEMBER
  • 2003 CHEVROLET MALIBU
  • 3.1L
  • V6
  • 2WD
  • AUTOMATIC
  • 195,000 MILES
The car itself overheats even after new water pump was installed, thermostat was installed, all relays and fuses were checked, system was bled out. Today I noticed the fans were not working. But would work if you turn the AC unit on. And if you turn the AC unit off the fan switch continue to work. Question is, why will the cooling fans not turn on when the temperature which is the point to need the cooling fans to be activated?
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Tuesday, August 7th, 2018 AT 8:23 AM

14 Replies

Tiny
PATENTED_REPAIR_PRO
  • MECHANIC
  • 1,853 POSTS
You might just have a faulty relay. Check the fuses first of all as shown in this diagram. Then if okay, try a new relay to the affected right or left fan.
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Wednesday, October 28th, 2020 AT 6:09 PM
Tiny
BRANDON STORCH
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  • 9 POSTS
All the fuses and relays are good to go, but still the fan will not come on and causing the engine to overheat unless the AC is turned on.
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Wednesday, October 28th, 2020 AT 6:09 PM
Tiny
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How do you know the relays are okay?
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Wednesday, October 28th, 2020 AT 6:09 PM
Tiny
BRANDON STORCH
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Brand new.
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Wednesday, October 28th, 2020 AT 6:09 PM
Tiny
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Okay, do you have a voltmeter or at least a 12 volt test light and a scan tool or code reader and if so are there any codes?
Also, which fan is it, left or right or both that does work when the AC is turned on?
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Wednesday, October 28th, 2020 AT 6:09 PM
Tiny
BRANDON STORCH
  • MEMBER
  • 9 POSTS
No codes, both fans fail to come on, but will work after the AC is turned on and will continue to work continuously after the AC has been turned off.
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Wednesday, October 28th, 2020 AT 6:09 PM
Tiny
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Have you done anything else such as replace the coolant temperature sensor?
So no P0480 or P0481?
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Wednesday, October 28th, 2020 AT 6:09 PM
Tiny
BRANDON STORCH
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  • 9 POSTS
Have not done that yet. Was next step.
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Wednesday, October 28th, 2020 AT 6:09 PM
Tiny
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Do you have a scan tool that can turn fans off and on?
If you do this step will both fans run on low speed or not?
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Wednesday, October 28th, 2020 AT 6:09 PM
Tiny
BRANDON STORCH
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No I do not.
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Wednesday, October 28th, 2020 AT 6:09 PM
Tiny
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Let me know if both fans run at low speed or not when doing this.
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Wednesday, October 28th, 2020 AT 6:09 PM
Tiny
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I think there would be a code set if it were a problem with the wiring. If the fans run in that test, I think you should give a new coolant temperature sensor a try.
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Wednesday, October 28th, 2020 AT 6:09 PM
Tiny
BRANDON STORCH
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I will pick one up on my way home see if it works. I will let you know.
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Wednesday, October 28th, 2020 AT 6:10 PM
Tiny
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Okay.
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Wednesday, October 28th, 2020 AT 6:10 PM

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