Is there a Radiator fan switch screwed into the cooling system somewhere or does the ecm control the fans?


Asked by Feb 23, 2014 at 11:22 PM about the 2004 Buick Rendezvous CXL FWD

Question type: Maintenance & Repair

I am usually pretty good at diagnosing my cars as I used to work as a tech for a GM dealer in the mid 90's... however I am quickly seeing that things have obviously changed...

I have a 2004 Buick Rendezvous with the 3.4 and it keeps running hot (221* on my scanner)  when my wife gets stuck in traffic... I noticed the fans were not coming on until 221* which I believe/feel is too late.  I also had a code P0128 which indicated my Coolant Temperature Below Thermostat Regulating Temperature so I replaced the Coolant temp sensor... It didn't change anything in regards to when the fans turn on.
I then replaced the serp belt due to cracks in it and while doing that I noticed some play in the water pump bearing so I replaced the water pump. It too didn't change anything in regards to it running hot in heavy traffic.
I have double checked the system is completely purged of air and everything else looks fine...  I remember all the GM's having one coolant temp sensor (for the ecm and gauge) and one radiator fan switch (turned on the fans) on all the electric fan vehicles back in the 90's but I can't find a Radiator fan switch on this Buick so I believe they now have the fans controlled by the ecm/pcm...   

I am also a bit concerned with how slow the fans run when they do turn on... Fans are coming on at approx 221* on my scanner and shutting off at 212* they only run for maybe 60 second and shut back off...  Of course I can leave the AC on max and they run continuously but again, they seem to be running at a slow speed and not moving much air.

If somebody could help me out here I sure would appreciate it... Thanks

17 Answers


Did you install a Delco coolant temperature sensor? I work at NAPA and we have trouble with GMs and aftermarket coolant temperature sensors. You are correct, the cooling fans are commanded on by the PCM. If your '04 Buick is like my '00 Grand Prix there's 3 fan relays. Two 4 pin relays and one 5 pin relay. The 4 pin relays are for each fan for low speed and the one 5 pin is for both fans high speed. With the 3.4 I'd check for a blown head gasket. These engines are notorious for that. HTH. -Jim

3 people found this helpful.

"code P0128 which indicated my Coolant Temperature Below Thermostat Regulating Temperature" Have you changed the thermostat or checked yours in hot water. It might be passing causing the engine to heat up. 221 is the trip point, they are operating normally. One sensor is the ECT that feeds the PCM, engine temp for fuel calculations and operates the fans. The other sensor is for the gauge or indicator light which ever the vehicle has.

5 people found this helpful.

JS08016.....I installed a Wells part which in my experience has always been a good product... After replacing the coolant temp sensor I no longer have the PO128... It doesn't have a blown head gasket. YET lol... It keeps running hot it may end up with one. Yetilikesbeer.... The code PO128 basically states that the vehicle is running "Below" the thermostat regulating temperature and is a strong indication the coolant temp sensor has failed. It is not sending a signal to the PCM setting the code... I replaced it and no longer have the code, however It continues to run hot in bumper to bumper traffic. Thanks guys, I appreciate the input.

2 people found this helpful.

I will also add that I have now replaced the Coolant temp sensor, Water Pump, Serp bent and Radiator cap... The Radiator looks very good and the car has always had Dexcool in it since it was new... I am going out to replace the thermostat now.

1 people found this helpful.

For warm up and highway traffic the coolant can be cooled by the rad as it passes through the faulty thermostat. As you hit heavy loads, high ambient temps or stop and go traffic the constant flow of passing fluid slowly heats up the entire coolant system. The rad is most efficent when the thermostat opens/closes allowing the stationary fluid to cool in the core, not just blast through. Trust me, I've had enough passing thermostats to know what happens, I'm to the point were I will not install the POS's untill I cycle them in a pot of water and confirm they open and close properly. For the code, there are multiple triggers in the ECU to trigger the code, there is most likely a runtime condition based on temp and running conditions to trigger it. I'm not bored enough to scroll through the code but I'm sure it's there. BTW If the fans triggered at the same time with the old ECT and the new one they are both good.

1 people found this helpful.

Test it in a pot of water. I pop them a few times then set them upside down and put water on the beast. If it drips toss it (a drip at 0 pressure is a spray at 12 ish). If it holds water it should be good.

1 people found this helpful.

You're welcome. Glad to help. -Jim


I bought a 2005 Buick Rendezvous, the mechanic has changed the radiator, the water pump, the thermostat, the temp switch and it's still running hot...Help!!!!

7 people found this helpful.

What is your definition of HOT....they want the engine to run hot, the emit less pollutants. Most GM cars have two fans, one come on when the engine gets up to temp, the second one come on when you turn on the a/ most cases they are wired so they are only running at 1/2 speed until the engine gets pretty in stop and go traffic...then around 230 degrees the fans get switched to high. You first need to determine how hot the engine is getting, are you loosing coolant? Then determine if both fans are working. Then notice their speed before the engine gets hot and after you think it is hot....are they running at two different speeds. Once you get all those answers you should know what to do next.

I to have a 2005 that stays over heating . Changed radiator cap thermostat new cooliant and bleed air out still overheats need help have a baby to drive around...

i got the same problem. im thinking new fans


By putting 12V directly to each fan you can verify that the fans are OK. You might check for a bad relay...owners manual might identify it and where it is...probably in the engine compartment and there is usually a chart on the inside of the cover identifying each relay. On most cars all the relays are the same so you can switch a couple of relays and if the problem goes with the relay you have found the problem.

2 people found this helpful.

This car is a piece of shit it overheats in traffic and even driving on the streets gm engineers did a horrible job in designing it it needs to be modified to be able to cool down im thinking add a air intake like setup on ghe hole by were the batery is and adding some sort of fan by the engine and another exit hole on. The oppisite side if anyone can think of how to be able to do it it would help everuone that owns thia veicle

2 people found this helpful.

I have a similar problem with my 06 Buick Rendezvous with 3.5L. I flushed the radiator and bled after refilling, replaced the thermostat and radiator cap, checked fuses and relays...all good. Now the car runs at just above 1/4 on the gauge but everyone now and then it spikes the needle to FULL OVERHEAT! I'll shut the car down and wait about an hour, start the car and all is good again - like nothing ever happened! I bought a new coolant temperature sensor but am having trouble locating where it goes. Do I need to remove the throttle body to get at it?

2 people found this helpful.

Is there any way to lower the trigger temp so my fan kicks on at a lower temp?

This a common problem for the Rendezvous. Try installing an adjustable fan controller.

I also own a 2003 rendenvous an ir to was running hot i watched the reserve water tank and noticed it was blowing bubbles in it toke the engine apart because its true these engines had a faulty head and intake manifold gasket that goes out at about 150,000 miles replaced both gasket put all fluids back perged air and got a lower opening thermostat and and replaced the water temp sensor and now it runs at 195 degrees been driving on it for 2 years no problems and if you have the know how to rebuild the engine it will only cost you about 350.00 to rebuild and put all fluid back it not then your looking at anywhere from 1100.00 to 2500.00 if you have to have a shop replace it almost forgot to tell the most important thing shave the heads down i did mine the old school way but any good machine shop will do it for you for 150 to 225 price wise

Your Answer:


Looking for a Used Rendezvous in your area?

CarGurus has 677 nationwide Rendezvous listings starting at $1,000.


Buick Rendezvous Experts

  • #1
  • #2
  • #3
    Tom Demyan
View All

Related Models For Sale

Used Chevrolet Equinox
1,231 Great Deals out of 88,471 listings starting at $995
Used Ford Escape
1,233 Great Deals out of 111,565 listings starting at $1,995
Used Ford Explorer
926 Great Deals out of 70,971 listings starting at $1,275
Used Nissan Murano
376 Great Deals out of 26,807 listings starting at $1,500
Used Honda Pilot
342 Great Deals out of 46,578 listings starting at $750
Used Honda Odyssey
438 Great Deals out of 34,867 listings starting at $1,200
Used Honda CR-V
760 Great Deals out of 76,925 listings starting at $100
Used Jeep Grand Cherokee
1,161 Great Deals out of 74,220 listings starting at $750
Used Chevrolet Malibu
622 Great Deals out of 51,591 listings starting at $1,550
Used Chevrolet TrailBlazer
78 Great Deals out of 3,431 listings starting at $988
Used GMC Envoy
43 Great Deals out of 1,602 listings starting at $1,990

Used Cars For Sale

2007 Buick Rendezvous CXL FWD For Sale
51 listings starting at $2,700
2006 Buick Rendezvous CXL FWD For Sale
23 listings starting at $1,971
2005 Buick Rendezvous CXL FWD For Sale
19 listings starting at $1,797

Content submitted by Users is not endorsed by CarGurus, does not express the opinions of CarGurus, and should not be considered reviewed, screened, or approved by CarGurus. Please refer to CarGurus Terms of Use.