Cooling fans not working correctly

2004 BUICK RENDEZVOUS
3.4L • 6 CYL • FWD • AUTOMATIC
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JESSEPATTY
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Cooling fans on my wife's Buick appear to be coming on to late and to slow to keep the car's temp down in heavy traffic.

Car ran quite hot last Friday (221* on my scanner) in heavy traffic tripping the SES/MIL light. I pulled codes and found a P0128 so I changed the coolant temp sensor and cleared codes.

Drove it for while with no MIL light and it ran right at 201* the entire drive.... I came home and let it idle and in about 5 minutes is was right back up to 224* at which time the fans came on at a very slow speed. They ran for 5 minutes dropping it to 217* when they shut off. I decided to go ahead and replace the serp belt due to cracks when I noticed some bearing play in the water pump so I replaced the water pump... purged the system of air and let it idle..... within 5 mins it was right back up to 224* at which time the fans came on at a slow speed again.....

I feel the fans are coming on way to late and at too slow a speed to be effective. If I understand correctly, this vehicle has 2-speed fans, if this is true, High speed is not working. I'll also point out that when the AC is on both fans run continuously at slow speed.

I've checked the two cooling fan fuses and they are good, I also checked three cooling fan relays by swapping them around and it made no difference so I think all the relays are working but I am not 100% sure.

Car does not run over 199-200* when the AC remains on and/or at night when it's cool out.... It's only doing it during low airflow through the radiator periods above 80*...

If you could shed some light on this issue I sure would appreciate it.

Thanks
Feb 23, 2014 at 9:39 PM
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HMAC300
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actually 221 isn't to bad a temp to worry about but check the connections on the pcm they may be corroded etc and the ground. when a/c is on is when other fan kicks on always. it can be either of these. also withengine off and fans disconnected feel for cold spots on radiator if there are then the rad is bad it should be about same temp all over.
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Feb 24, 2014 at 7:15 AM
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JESSEPATTY
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Thank you....

I understand 221 isn't terrible but once it gets there it tends to keep climbing in stop and go traffic... I have her car today to figure it out and earlier I took a 30 minutes ride and as long as I was moving it stayed right around 199-202 on my scanner... As soon as I stopped for a light or something it began to climb quickly.

I've changed the Coolant temp sensor, radiator cap, Serp belt and water pump thus far... I'm going to go change the thermostat now and see what that does... I was trying to put that off because so much has to come off to replace it

Thank you, I appreciate the input.
Feb 24, 2014 at 10:04 AM
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STRAILER
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It sounds like the PCM is not triggering the high speed relay can you use a test light to see if a trigger signal is being sent when the engine is hot? Use the wiring diagram above and this guide.

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

Please run this test and get back to us so we can continue helping you.

Best, Ken
Mar 2, 2017 at 11:30 AM
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REY-GTS
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Thanks for this post it was the PCM on my car had to replace it cost me $640.00
Nov 29, 2018 at 6:20 PM
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AARONPTRSN
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My AC has been blowing warm air. Ive checked fuses and also freon. The clutch just stopped working for compressor. Also my cooling fans wont work. They do work when i hard wire right to battery. Help please.
Nov 30, 2018 at 11:29 AM (Merged)
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JACOBANDNICKOLAS
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Check to see if there is power to the clutch. If there is, then the clutch is bad. If there isn't, check the cycle switch.
Nov 30, 2018 at 11:29 AM (Merged)
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MARK FRIZZELL
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with solus I can manually initiate high and low speeds on fans. also, have replace ECT, and relay, still no luck, except I can remove five pin relay an throw a ground load on terminal 85 where relay plugs in and initiate fans. also, no codes appear on DTC,
Nov 30, 2018 at 11:29 AM (Merged)
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MARK FRIZZELL
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I also have run continuity test from ECM to relays and ECT all those wires are good. all grounds good.
Nov 30, 2018 at 11:29 AM (Merged)
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HMAC300
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it may be the fuse box problem or corrosion. try tweaking the prong on the relay and see if it will make contact. also, look for corrosion on plug in, try some dielectric grease on prongs of relay.
Nov 30, 2018 at 11:29 AM (Merged)
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MARK FRIZZELL
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I don't seem to be getting a signal from pcm to turn on the fans, is there any difficulty with installing a used pcm from same car?
Nov 30, 2018 at 11:29 AM (Merged)
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MARK FRIZZELL
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I didn't mention that this vehicle has a stalling type problem at acceleration, like is loading or choking it starts fine, idles fine, no codes , you basicly couldn't pass someone, does ok up to 30-40mph, if you accelerate hard it falls on its face
Nov 30, 2018 at 11:29 AM (Merged)
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HMAC300
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for the acceleration thing check fuel pressure with a gauge may be low. if you put old pcm in it should be ok if not then it would be security if no start. also clean throttle plate on both sides and iac with choke cleaner.
Nov 30, 2018 at 11:29 AM (Merged)
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CANDACE NICHOLS
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I have ground running to passenger side fan but no ground to drivers side fan or window. thinking it is a common ground or PCM is not grounding any clues? Also, I have no wiring diagrams to help. I believe the engine was swapped.
Nov 30, 2018 at 11:29 AM (Merged)
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HMAC300
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the main ground is on a stud at back of engine to transmission easy to spot. because of size I had to show diagram in two pictures. check all fuses, and relays ground is in center of engine. Also, check coolant temperature switch for resistance it may be bad. also is partial ECT sensor resistance, but you should get the idea on temperature etc.
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Nov 30, 2018 at 11:29 AM (Merged)
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LOVER BOY
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Electric cooling fans not working. Here's what I have checked already...fan fuses are still good, and fuse circuits are showing 12 volts when checked with volt meter. I checked fan plug with volt meter and didn't get a reading. So, I'm not sure if there's a relay switch or sensor for the fan to come on at a certain temp or is it just a bad cooling fan. What should I do?
Nov 30, 2018 at 11:29 AM (Merged)
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HMAC300
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try switching the relay with a like relay it's underhood and should be marked on inside top cover there are 3 relays 1-2-3 2 & 3 deal with high speed. also check the ground on rih side so fengine
Nov 30, 2018 at 11:29 AM (Merged)
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LOVER BOY
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Thank you for the answer car pros! Is it any kind of way you can send me a schematic or under hood image of wear the relays are under the hood
Nov 30, 2018 at 11:29 AM (Merged)
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HMAC300
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they are in the underhood fuse box and should be marked on inside of top cover.
Nov 30, 2018 at 11:29 AM (Merged)
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NEWMAN39US
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Engine Cooling problem 6 cyl Front Wheel Drive Automatic 130000 miles

My car is overheating and it appears that the 2nd cooling fan is not coming on. I have run direct power and it does work. I have checked fuses and relays and they are good. What should trigger the fan to come on?
Nov 30, 2018 at 11:29 AM (Merged)
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DOCFIXIT
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Hi
There are three fan relays what grounds relay for high speed fan is the PCM. Also two cooling fan fuses. What method of testing relays was used?
Let me know
Nov 30, 2018 at 11:29 AM (Merged)
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NEWMAN39US
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There are 4 relays that are the same in the engine comparment fuse box. I moved them to different positions with no change to anything so I assumed that is not the problem. Also swapped the 2 fuses. Is there a good way to check relays?
Nov 30, 2018 at 11:29 AM (Merged)
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DOCFIXIT
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Swaping is good with know good relay. Then PCM controls relay so need scan tool to check if relay is being activated
Nov 30, 2018 at 11:29 AM (Merged)
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NEWMAN39US
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I will have that checked. Thanks for your help
Nov 30, 2018 at 11:29 AM (Merged)
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NEWMAN39US
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One more question - when should the 2nd fan come on?
Nov 30, 2018 at 11:29 AM (Merged)
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JOLMO
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1) my high speed cooling fan does not turn on when driving or when I shut off the car and it starts to overheat.
2) I also looking for the location of the thermostat.
Nov 30, 2018 at 11:29 AM (Merged)
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DOCFIXIT
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With AC and if coolant rises above 220 deg. If AC is Auto maybe AC conroler telling PCM AC is on.
Nov 30, 2018 at 11:29 AM (Merged)
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KHLOW2008
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Hi jolmo, Thank you for the donation. Are the fans operating at low speed conditions? Have you checked the cooling Fan relay # 2 and # 3? Thermostat is located behind the housing of the outlet hose. WATER OUTLET HOUSING REPLACEMENT 1. Remove the air cleaner and duct assembly. 2. Drain the coolant until the coolant level is below the thermostat. 3. Remove the crossover exhaust pipe. 4. Remove the radiator hose from the thermostat housing. 5. Remove the thermostat housing bolts and clean any sealer from the bolt threads. 6. Remove the thermostat housing and gasket.


https://www.2carpros.com/forum/automotive_pictures/192750_Thermostat03RendezvousFig68_1.jpg

7. Remove the thermostat. 8. Clean the mating surfaces.
Nov 30, 2018 at 11:29 AM (Merged)
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NEWMAN39US
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Perfect -thanks very much for your help. Have a great day!
Nov 30, 2018 at 11:29 AM (Merged)
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JOLMO
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yes my fans are operating at low speed.
Nov 30, 2018 at 11:29 AM (Merged)
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KHLOW2008
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Here is a schematic of the cooling system. Check the fan relays 2 and 3.


https://www.2carpros.com/forum/automotive_pictures/192750_CoolingFan03RendezvousFig10a_1.jpg


https://www.2carpros.com/forum/automotive_pictures/192750_CoolingFan03RendezvousFig10b_1.jpg

Nov 30, 2018 at 11:30 AM (Merged)
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CANDACE NICHOLS
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The fans not coming on i think its a common ground I have ground to the left side fan but not to the drivers side fan and no ground to drivers side window as well I have no wiring diagram any clues?
Nov 30, 2018 at 11:30 AM (Merged)
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STRAILER
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Hello,

I have found this cooling fan wiring diagram (below) for you and a guide to help you get the problem fixed.

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

and

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

Please run some tests and get back to us so we can continue helping you.

Cheers, Ken


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Nov 30, 2018 at 11:30 AM (Merged)
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S_BRONSON
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Cooling fans not operating when a/c not running. Car overheats and may or may not start when hot. Turns over at normal speed but won't crank. vapor lock? computer? Help!
Nov 30, 2018 at 11:30 AM (Merged)
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XOWEY
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well first, the fans don't come on till the engine temp is around 130 F..............if it's not going into the red, it's not really overheating. this issue, we need to address first, many people assume that their car is overheating if the temp goes high when they are working on it. how high does the temp go when you drive it?

as far as the no start..........under the vehicle there is a connector that plugs into the floor on the drivers side just behind the drivers seat area, check there for any green corrosion/
Nov 30, 2018 at 11:30 AM (Merged)
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SHOCKY22
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The Cooling Fans In My Vehicle Aren't Turning On And I Have Changed The Relay, What Else Could Be Causing Them To Not Turn On?
Nov 30, 2018 at 11:30 AM (Merged)
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JACOBANDNICKOLAS
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Check the sending unit and wiring.
Nov 30, 2018 at 11:30 AM (Merged)
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JAMES GILLIS
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At idle engine temperature hits just above half way fans do not come on at all. wired direct runs normal temperature. I was needing to know if and where the fan control sensor is located? Oh, it has new head gaskets water pump thermostat and radiator, before anyone asks. lol.
Nov 30, 2018 at 11:30 AM (Merged)
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HMAC300
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the engine coolant temperature sensor tells PCM when to put fans on check fuse and relay in under hood fuse box. but you did not put engine size so we cannot tell you where it is.
Nov 30, 2018 at 11:30 AM (Merged)
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JAMES GILLIS
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I am sorry it is a 3.4 liter V6.
Nov 30, 2018 at 11:30 AM (Merged)
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HMAC300
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it is by the thermostat housing on drivers side rear of engine. see picture.
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Nov 30, 2018 at 11:30 AM (Merged)