Coolant fan problem, getting hot

Tiny
DON SALTER
  • MEMBER
  • 2005 PONTIAC MONTANA
  • 3.4L
  • 6 CYL
  • 2WD
  • AUTOMATIC
  • 150,000 MILES
Have the vehicle listed above (same as the 2004 model). Noticed a few months back that the engine was running hot, not overheating, but getting close. When in stop and go traffic, the needle would rise (220 F and higher) and when moving, come down.

Had mechanic look it over. Replaced thermostat and checked system out and could not figure it out.

I decided to check the fans and they do not seem to be working properly. When I start the car and turn the AC on, neither fan comes on. AC did not seem to be cold either.

I unplugged the coolant sensor cable and started the car with AC on and fans came on briefly, maybe thirty seconds and shit off.

I left the sensor unplugged and tried again and fans would not come on.

I plugged it back in and still no fans.

Warmed the car up to about 235 F (according to my scan unit) and fans do not kick on.

I am going to investigate the fuses and relays next.

Currently, there is no visible leaks of coolant and my dipstick is clean - only oil. I think my head gasket is okay.

Any thoughts? Thanks!
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Wednesday, April 17th, 2019 AT 12:45 PM

5 Replies

Tiny
JACOBANDNICKOLAS
  • EXPERT
Welcome to 2CarPros.

I agree with you. The head gaskets don't seem to be the issue. The fans should come on. Also, if it doesn't overheat at highway speeds, then you know if it fan related.

With that, I have attached diagnostic flow charts. There are three of them that walk you through a process, but you need a scanner to perform the test. If you do, take a look through them.

If you don't first check fuses 1 and 6 in the under hood fuse box. See picture 4. If they are good, then remove the fan relays. There are a total of 3 of them. (relays 9, 10, and 13.) Picture 4 shows the lay out of the fuse box under the hood.

Here are directions for checking fuses and relays. Also, how to use basic test equipment.

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

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

https://www.2carpros.com/articles/how-to-check-an-electrical-relay-and-wiring-control-circuit

https://www.2carpros.com/articles/how-to-use-a-test-light-circuit-tester

https://www.2carpros.com/articles/how-to-use-a-voltmeter

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

____________________________________-

Let me know if you have questions or need help.

Take care,
Joe

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Wednesday, April 17th, 2019 AT 7:21 PM
Tiny
DON SALTER
  • MEMBER
Thanks for the reply. So I was at it again tonight. Took my multi-meter and tested the fuses and relays and they checked out fine.

I decided to again unplug from the cooling sensor and the fans both came on. And they continued to run.

Plug back in and turned on ac and fans do not come on. Again unplugged with no AC on and fans kicked in.

I will review what you send. Sadly I have limited tools but am suspecting perhaps the coolant sensor.
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Wednesday, April 17th, 2019 AT 7:26 PM
Tiny
JACOBANDNICKOLAS
  • EXPERT
Welcome back:

Let me know what you find or if you have other questions.

Take care,
Joe
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Wednesday, April 17th, 2019 AT 7:56 PM
Tiny
DON SALTER
  • MEMBER
Quick question based on what I have found thus far that when the coolant temperature sensor wire is unplugged the fans come on but do not work when plugged in even with the AC on. Could it be the coolant temperature sensor being bad?

That is, does the coolant temp sensor need work properly when I turn AC on? And if it is bad even turning AC On the won t help?
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Thursday, April 18th, 2019 AT 8:20 AM
Tiny
JACOBANDNICKOLAS
  • EXPERT
When you turn the AC on, power is supplied through a different relay. The sensor doesn't actuate it with the AC. By unplugging the sensor, the computer doesn't see any signal. As a result, it goes into a protective mode and turns them on to prevent damage.
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Thursday, April 18th, 2019 AT 8:16 PM

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