My radiator cooling fan is not working why?

Tiny
FORDMAN969
  • MEMBER
  • 2005 BUICK CENTURY
  • 3.1L
  • 6 CYL
  • 2WD
  • AUTOMATIC
  • 150,000 MILES
Just recently replaced the head gaskets (overheating blew gasket), temperature sensor, both fan motors, heater core and the radiator. Driver side fan kicks on just after coolant starts boiling and passenger side weakly tries to start but can't go as fast. I've checked all fuses and relays related to the fans and they're all good, max A/C should kick on passenger side but doesn't. I need advice and things to check.
Tuesday, May 12th, 2020 AT 1:55 PM

30 Replies

Tiny
KASEKENNY
  • MECHANIC
  • 18,907 POSTS
This is most likely one of two issues based on everything you replaced. Either you have an issue with the PCM not commanding them on the proper speed, or you have resistance in the wiring.

Try jumping 12 volts directly to each fan motor to ensure they are capable of spinning at high speed.

If they can, then you are not getting 12 volts to them when you should. Again, either the control module is not sending 12 volts or the wiring has high resistance not allowing the motors to get 12 volts.

You can confirm this by measuring the voltage you have at each fan when the A/C is on and the coolant temp get higher. Both fans should be on high at this point.

At that point, you want to measure resistance from the relay to the motor. Then to the PCM.

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

Let me know what questions you have. Thanks
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Tuesday, May 12th, 2020 AT 2:41 PM
Tiny
AKRACKER419
  • MEMBER
  • 1 POST
  • 2004 BUICK CENTURY
  • 3.1L
  • 6 CYL
  • FWD
  • 110,000 MILES
My cooling fan does not come on at all regardless if my A/C is on or not. I would think that it would kick on after my temperature gauge reached half way or better but still nothing? Why will it not come on?
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Wednesday, May 26th, 2021 AT 12:18 PM (Merged)
Tiny
STEVE W.
  • MECHANIC
  • 13,321 POSTS
GM fans in that vehicle turn on at 223 degrees and turn on for the AC if the air temperature is over 122 degrees. The only item you may want to check is the actual AC pressures and the pressure switch. It should activate at pressures over 190 psi. And turn on the fan. If you have access to a shop or an OEM level scan tool you can test the fans operation very easily and without touching anything under the hood until you have determined if there is a problem.
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Wednesday, May 26th, 2021 AT 12:18 PM (Merged)
Tiny
PATCAL096
  • MEMBER
  • 2 POSTS
  • 2003 BUICK CENTURY
  • 3.1L
  • V6
  • FWD
  • AUTOMATIC
  • 101,560 MILES
The cooling fans are not coming on unless I turn on the A/C. I have a obd2 adapter, using Torque Pro I checked the coolant temperatures to see if the fan came on at the right temperature. It got up to 221 F without the fans coming on. I have not coolant loss and all my hoses are uniformly warm. No cold spot in the radiator that I could find. I also pulled and reseated the three fan relays with no change. Not sure how to check the relays without buying new ones. Any thoughts? Thanks.

Pat Callaghan
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Wednesday, May 26th, 2021 AT 12:18 PM (Merged)
Tiny
CARADIODOC
  • MECHANIC
  • 33,788 POSTS
221 degrees is not hot enough for most GM vehicles. They need to get much hotter than other brands before the radiator fan will turn on. I always remember 226 degrees, but some experts say it can be even higher.

On most cars you can force the engine computer to turn on the radiator fan by unplugging the two-wire coolant temperature sensor. Turning the fan on is the default in case the engine is getting too hot. The computer will not know it, so it runs the fan to be safe. Doing that will set a diagnostic fault code. There is nothing to worry about, but it is a good idea to erase that code so it will not confuse someone in the near future. The only part of the circuit you are not testing this way is the sensor itself, but failures of temperature sensors is extremely uncommon because there is just one part inside them. Corroded connector terminals that add resistance to the circuit is more common than a failed sensor. That corrosion typically will not cause an incorrect temperature reading of just a few degrees. It is more likely you would see something around 100 to 150 degrees, and it is even more likely you would have an erratic idle speed tracking the erratic sensor readings.
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Wednesday, May 26th, 2021 AT 12:18 PM (Merged)
Tiny
PATCAL096
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Thanks for the reply. Wow! I thought 221 was hot. I was going to pull and test the relays tomorrow but I will retest with a little higher temperature. The thing is, the care was not this way when I got it last August. The temperature gauge was always less than half. Then this spring this started. Maybe I am paranoid but I want to know those fans are coming on without the A/C. I will update tomorrow.
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Wednesday, May 26th, 2021 AT 12:18 PM (Merged)
Tiny
JERRY98
  • MEMBER
  • 6 POSTS
  • 2003 BUICK CENTURY
  • 6 CYL
  • 48,000 MILES
I let my car run today at idle for an extended time and noticed my radiator fans never did come on, the temp gauge stayed around the notch below the halfway mark, never did go much beyond that mark. The hoses was hot but the fans never did come on. Is this normal? Can a car keep itself cooled enough on its own without the fans running? No signs that the car is overheating. I recently had a coolant flush (routine) and last year a new thermostat installed. The fans work fine when the AC is turned on.
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Wednesday, May 26th, 2021 AT 12:18 PM (Merged)
Tiny
SATURNTECH9
  • MECHANIC
  • 30,869 POSTS
The fans dont come till 222-228 depending on what the computer is programed to turn them on at. So if the temp didnt hit the correct temp the fan wont come on. If it didnt boil over thats a good sign. If you want to get a infared temp we can check and see how hot its getting etc.
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Wednesday, May 26th, 2021 AT 12:18 PM (Merged)
Tiny
JERRY98
  • MEMBER
  • 6 POSTS
The fans finally came on after a 20 mile trip then letting it idle. The temperature gauge went past the half way mark (almost to the next notch) before they came on and then cooled down to the notch below the half way mark. But thanks for your advice, now you have me interested in one of those infared guns:)
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Wednesday, May 26th, 2021 AT 12:18 PM (Merged)
Tiny
SATURNTECH9
  • MECHANIC
  • 30,869 POSTS
You can get a pretty nice infared gun on amazon pretty cheap.I recommend a ray tech one I bought when they first came out.I have since like 1994 or 1995 and still works great.
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Wednesday, May 26th, 2021 AT 12:18 PM (Merged)
Tiny
GORDON321
  • MEMBER
  • 1 POST
  • 2003 BUICK CENTURY
I just replaced the thermostat, radiator cap, coolant sensor, and checked all relays on my car. The cooling fans still are not coming on when the car reaches normal temperature. Then it starts to go past the normal temperature and the fans will not come on but when I unplug the coolant sensor or turn the air conditioner on both fans come on. Is there another sensor, switch or anything else that controls the fans? If so what and where is it located? Please respond ASAP. By the way nothing is stopped up.
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Wednesday, May 26th, 2021 AT 12:18 PM (Merged)
Tiny
BLUELIGHTNIN6
  • MECHANIC
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Three cooling fan relays and an engine coolant temperature sensor are easiest and cheapest on the circuit that could cause this issue. If they have been checked/replaced already than all that is left is the power-train control module (PCM).
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Wednesday, May 26th, 2021 AT 12:18 PM (Merged)
Tiny
DOUG S.
  • MEMBER
  • 1 POST
  • 2002 BUICK CENTURY
  • 6 CYL
  • FWD
  • AUTOMATIC
  • 140,000 MILES
It seems that my cooling fans are not coming on properly. They do work, I have replaced three relays and a fuse on the car. The temperature gauge will go up to the 3/4 mark, then the fans come on but only cool it down the the 1/2 mark. If I am driving on the highway, the temperature gauge stays between 1/4 and 1/2 mark. Also, I did replace the fans. Is this normal for this car? I have only had the car for three months?
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Wednesday, May 26th, 2021 AT 12:18 PM (Merged)
Tiny
JDL
  • MECHANIC
  • 16,098 POSTS
Hello,

I would try replacing the engine coolant temperature sensor which controls the fans via the PCM. Here is the fan wiring diagrams so you can see how the system works and the location of the sensor with a guide to show you the steps to replace it:

https://www.2carpros.com/articles/coolant-temperature-sensor-cts-replacement

Check out the diagrams (below). Please let us know what happens.

Cheers
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Wednesday, May 26th, 2021 AT 12:18 PM (Merged)
Tiny
LVZNLO
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  • 0 POST
I got the sensor for $28.00 it fixed the problem!
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Wednesday, May 26th, 2021 AT 12:19 PM (Merged)
Tiny
JOSEPH RANDALL
  • MEMBER
  • 1 POST
Dude. I just happened on your post!
Yes! I have the exact crazy symptom! Car I could swear when first got it always showed lower than halfway mark? Under load up hills, sitting, my scan tool indicates they come on at 215F, and I pressure tested, replaced thermostat (only cause of dumping sealer in it), I've bled system, freaked thinking it was the TSB with head gasket, but it holds pressure, comes back down, and only goes to 3/4 past. But to me. This isn't normal and I never saw this working on any model?
Suggestion. I'm installing a switch and using the signal area at relay. Basically I'm making my own ground I can turn on in traffic and if I need to? It makes no sense? Don't have combustion in system, don't have air in it, fans turn on with A/C request, it simply reads way higher than I consider normal?
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Wednesday, May 26th, 2021 AT 12:19 PM (Merged)
Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
  • 44,198 POSTS
The fans come on at 225-230 in that car, does it overheat boil over? We should do a chemical check for the head gasket this guide can help us:

https://www.2carpros.com/articles/head-gasket-blown-test

Please run down this guide and report back.

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Wednesday, May 26th, 2021 AT 12:19 PM (Merged)
Tiny
DEANLANDIS
  • MEMBER
  • 1 POST
  • 1998 BUICK CENTURY
Electric cooling fans will not turn on when engine gets too hot. I checked the fuses and relays. They are good. I replaced the CTS and it did not fix the problem. I did discover that if I disconnect the electrical connector to the CTS, the electric fans will turn on and stay on. I have left the connectors disconnected temporarily so that the engine does not over heat. In doing this, I've noticed a drop in gas mileage. Please help. Oh, the radiator fluid level is good.
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Wednesday, May 26th, 2021 AT 12:19 PM (Merged)
Tiny
HMAC300
  • MECHANIC
  • 48,600 POSTS
The reason your gas mileage dropped is you disconnect the cts and it doesn't control the fans. plug it back in. There are 3 relays not 2 and 2 large fuses. they all must be checked. I'm including a diagram. If it's not a relay, then you'll have to have a pro check it for a bad connection or shorted wire coming from or to the pcm....

Heres a guide on checking relays and one on testing wiring, they will help you figure this out

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

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


https://www.2carpros.com/forum/automotive_pictures/406719_relay_diag_1.jpg

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Wednesday, May 26th, 2021 AT 12:19 PM (Merged)
Tiny
DOUGLASEBOGGS
  • MEMBER
  • 1 POST
The relay was bad thank you.
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Wednesday, May 26th, 2021 AT 12:19 PM (Merged)

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