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radiator cooling fans constantly running


jp628
08-09-2005, 06:23 PM
Someone please help me, have a 95 Buick LeSabre Limited/with a 3.8. The radiator cooling fans are constantly running with key on. They only go off when you turn the key off. If anyone knows what the problem is, would be greatly appreciated. Thank you.

yogi_123rd
08-09-2005, 10:33 PM
The fan system has two speeds - slow and high speed. The slow speed system is used with the AC, the high speed system is used when the engine is hot. There are two relays involved located on the inside driver side fender wall near the radiator. Both these relays are the same part number and can be swapped. One relay is for the slow speed and one relay is for the high speed circuit. The ECM controls both of these relays based on if the AC is on (slow speed) and the temperature switch on (high speed) which is located in the intake manifold behind the throttle body.

When you turn the AC on, the fans should constantly run at low speed. This is would be normal (if you want your AC to work).

Now, testing with your AC turned off, if the fan is running at slow speed, find the relay that controls that circuit (disconnecting it will stop the fans) and
swap it with the other relay. If the fans stop, the relay is bad.

If the fans are running at high speed - do the same to check the relay. You also may have a bad temperature switch that could possibly be shorted telling the ECM to run the high speed circuit causing the same problem.

The problem can also be the ECM itself as it controls the relays. You can hear a click when the relay is activated. In my 90 Lesaber, my slow speed circuit runs constantly and I know the problem is in the ECM

mcqueary
08-09-2005, 10:35 PM
The coolant fans are controlled by two relays in the engine compartment near the firewall. The two coolant relays are the ones closest to the driver's side. The relay on the driver's end controls both fans (driver's side runs in low speed) and the relay next to it is for the driver's side fan in high speed mode. Power is provided to the relay coil when the key is on. The car's computer tells the relays to turn on by grounding the other side of the relay coil. It sounds like the computer is telling the fans to turn on because the computer thinks the engine is hot or the A/C is on or because of a computer malfunction. A short to ground is another possibility.

Is your service engine soon light on? Does this happen even when you first start the engine when it's cold?

jp628
08-10-2005, 05:55 AM
The check engine light has never come on with the engine running. The fans are running even when the motor is cold. Sometimes they run on high speed, sometimes they run on low speed with a/c off. thanks for reply. Anything else would be appreciated.

mcqueary
08-10-2005, 08:56 AM
My guess is that your computer (PCM) is bad. In particular the circuits that control the fans (called the quad driver number 4 or QDM #4) is probably bad. By the way QDM #4 also controls the air conditioner relay so it's possible you may have problems here also later on. When this part of the PCM goes bad the service engine soon light will not come on but diagnostic trouble code P1670 should be stored in the computer memory. You could verify this if you were able to read the trouble codes. Unfortunately, the codes on the 1995 are hard to read if you do not have the correct scan tool and even many service shops (and most Autozones) do not know how to read them. A regular OBDC-II scanner will not read the codes although it can be plugged in to the 16 pin connector under the driver's side dashboard OK.

One possible plan is to have the codes read at a Buick dealer (ask them first how much this would cost). If they confirm code P1670 and say you need a PCM, they can replace it (I estimate 3 to 4 hundred dollars) or you may be able to find a used one on ebay (75 - 150 dollars) if you are paitient and replace it yourself.

Or you may just decide to live with the problem. If you live in a cold weather climate, having the fans on all the time may not allow your engine to warm up properly. Otherwise having the fans on will just be a nuisance. It's also possible the QDM#4 circuit may fail open and you will have no fans which is a major problem.

kok328
08-10-2005, 05:43 PM
Ebay? Wouldn't the local salvage/junk/bone yard suffice and be cheaper (depending, for me I live in Buick city and parts are a dime a dozen)?

jp628
08-10-2005, 06:21 PM
i got home from work today and the fans were off, i shut the motor off and turned the key to the on, position and they stayed off(the fans) would the pcm do this even though it is going bad?

mcqueary
08-10-2005, 11:55 PM
Do you mean the fans never come on now or are they coming on and going off when they are supposed to? If the problem is intermittent, I think the problem could still be the PCM. And I agree with the previous poster that if you have access to a junkyard, check there for a PCM.

jp628
08-11-2005, 04:53 AM
i don,t know whats going to happen with them now, i,ll see what happens today going to work and back, all i know is that they were off when i got home, and stayed off when key was turned to on, with engine off, this is a first for this , i,ll let you know tonite, do i have to get a pcm out of a lesabre or will one work out of a park av.? can you tell me what years and makes will work in mine and what all is involved switching pcm,s. thanks

jp628
08-12-2005, 05:50 AM
well second day in a row everything is back to normal fans are going off now they run with the a/c on and shut off when a/c is turned off. does the pcm correct its own problems? i,ll let you know of any changes and thanks for all your advise.

jp628
08-12-2005, 09:43 PM
third day, all is well

jp628
08-13-2005, 07:25 PM
4th day and all is ok

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