Cooling fans not working correctly

Tiny
JESSEPATTY
  • MEMBER
  • 2004 BUICK RENDEZVOUS
  • 3.4L
  • 6 CYL
  • FWD
  • AUTOMATIC
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
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Sunday, February 23rd, 2014 AT 9:39 PM

40 Replies

Tiny
HMAC300
  • EXPERT
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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Monday, February 24th, 2014 AT 7:15 AM
Tiny
JESSEPATTY
  • MEMBER
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.
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Monday, February 24th, 2014 AT 10:04 AM
Tiny
KEN
  • ADMIN
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
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Thursday, March 2nd, 2017 AT 11:30 AM
Tiny
REY-GTS
  • MEMBER
Thanks for this post it was the PCM on my car had to replace it cost me $640.00
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Thursday, November 29th, 2018 AT 6:20 PM
Tiny
AARONPTRSN
  • MEMBER
  • 2004 BUICK RENDEZVOUS
  • 130,000 MILES
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.
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Friday, November 30th, 2018 AT 11:29 AM (Merged)
Tiny
JACOBANDNICKOLAS
  • EXPERT
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.
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Friday, November 30th, 2018 AT 11:29 AM (Merged)
Tiny
MARK FRIZZELL
  • MEMBER
  • 2005 BUICK RENDEZVOUS
  • 3.4L
  • V6
  • FWD
  • AUTOMATIC
  • 162,000 MILES
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.
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Friday, November 30th, 2018 AT 11:29 AM (Merged)
Tiny
MARK FRIZZELL
  • MEMBER
I also have run continuity test from ECM to relays and ECT all those wires are good. All grounds good.
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Friday, November 30th, 2018 AT 11:29 AM (Merged)
Tiny
HMAC300
  • EXPERT
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.
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Friday, November 30th, 2018 AT 11:29 AM (Merged)
Tiny
MARK FRIZZELL
  • MEMBER
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?
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Friday, November 30th, 2018 AT 11:29 AM (Merged)
Tiny
MARK FRIZZELL
  • MEMBER
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
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Friday, November 30th, 2018 AT 11:29 AM (Merged)
Tiny
HMAC300
  • EXPERT
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.
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Friday, November 30th, 2018 AT 11:29 AM (Merged)
Tiny
CANDACE NICHOLS
  • MEMBER
  • 2002 BUICK RENDEZVOUS
  • 3.4L
  • 6 CYL
  • 4WD
  • AUTOMATIC
  • 100,000 MILES
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.
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Friday, November 30th, 2018 AT 11:29 AM (Merged)
Tiny
HMAC300
  • EXPERT
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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Friday, November 30th, 2018 AT 11:29 AM (Merged)
Tiny
LOVER BOY
  • MEMBER
  • 2002 BUICK RENDEZVOUS
  • 6 CYL
  • 2WD
  • AUTOMATIC
  • 160,000 MILES
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?
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Friday, November 30th, 2018 AT 11:29 AM (Merged)
Tiny
HMAC300
  • EXPERT
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
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Friday, November 30th, 2018 AT 11:29 AM (Merged)
Tiny
LOVER BOY
  • MEMBER
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
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Friday, November 30th, 2018 AT 11:29 AM (Merged)
Tiny
HMAC300
  • EXPERT
They are in the underhood fuse box and should be marked on inside of top cover.
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Friday, November 30th, 2018 AT 11:29 AM (Merged)
Tiny
NEWMAN39US
  • MEMBER
  • 2002 BUICK RENDEZVOUS
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?
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Friday, November 30th, 2018 AT 11:29 AM (Merged)
Tiny
DOCFIXIT
  • EXPERT
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
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Friday, November 30th, 2018 AT 11:29 AM (Merged)

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