How to test the electro-viscous fan clutch

Mooseman

Moderator
So you suspect that your fan clutch is defective. One of two conditions is possible.

If your fan is roaring like a jet engine after it has warmed up, DO NOT TEST. It's already confirmed that the clutch is locked up and needs to be replaced. Normally, it will roar a little on startup and should quiet down as it warms up. If it is locked up, it's not bad to run it like this but power and fuel consumption will suffer and you may get a CEL with a code about the fan speed.

The other possible condition is that the fan is not working enough. The engine may or may not be getting overheated but a lot of times, A/C performance will suffer while idling but will be better while moving. You may or may not be getting a CEL with a fan code. It might not be overheating because the residual friction is spinning the fan just enough to pull a little bit of air. Here's how to test for this condition.

  1. Warm up the engine completely

  2. Turn on the A/C
  3. Try to stop the fan using a rag like in the video below
  4. Hold it for a little bit. You should feel some tugging from the fan trying to get it going again
  5. If you are getting that tugging, the clutch is working. If not, it's defective.
  6. If the temperature gauge is starting to climb and the fan is still not working, let go of the fan and turn on the heater to cool the engine
If it's winter or your A/C doesn't work (i.e. it's empty), use this alternative method:

  1. Turn off the heater and warm up the engine completely
  2. Stop the fan using a rag like in the video below
  3. Because the engine is at normal operating temperature, the PCM will not command the fan to run right away. Keep holding it while the engine gets hotter
  4. As it gets hotter, you should start feeling some tugging from the fan trying to get it going
  5. If you are getting that tugging, the clutch is working. If not, it's defective.
  6. If the temperature gauge is starting to climb and the fan is still not working, let go of the fan and turn on the heater to cool the engine



An extra test to do while holding the fan, try to push the fan edge fore and aft. If it moves more than about 1/8", the bearings inside the clutch are failing. It might also make you think that the clutch is working because of this wobble and failing bearings due to extra friction.

If your engine is not overheating, you can continue to run it like this until a replacement clutch can be ordered and installed. You might get a CEL but keep an eye on your engine temperature, especially if the weather is warm/hot and avoid using the A/C. Hayden is the preferred brand here while Dorman have been known to fail prematurely, despite their lifetime warranty.
 
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littleblazer

Gold Supporter
Hmmmmm..... that truck looks awfully familiar. :biggrin: Nice write up. :thumbsup:
 
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Mooseman

Mooseman

Moderator
Hope you don't mind me referencing your video? I keep using it as an example on how to test the fan so thought it would be prefect for this article.
 

littleblazer

Gold Supporter
Not at all, I'm glad its useful.
 
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Mooseman

Mooseman

Moderator
I just want to add another thing to check before declaring the clutch dead. Swap the fan relay with another similar one in the fuse box (headlight IIRC) and see if the problem persists. One last thing, check the wiring, especially at the clutch connector to ensure there are no broken wires.
 

swede

Well-Known Member
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Mooseman

Mooseman

Moderator
You could put +12V to the white wire, which will effectively put the fan to 100% engagement but my method will also show if it works at partial engagement. The PCM never puts it to 100%, 90% is the highest and that's at very high engine temps. It may work at 100% but maybe not at 20-30%.

Of course the absolute best way to test is with a Tech 2.
 

webdawg

Well-Known Member
Okay, so in your other post to me about testing it you say that the one in this video is bad. The one in this video is bad? I am going to do a re test of mine, I think it is bad and I want to be sure.
 
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Mooseman

Mooseman

Moderator
I found this video by Scanner Danner where he's trying to diagnose a fan code. Shows the signals to and from the the fan and how the fan operates when commanded by the PCM and the scanner. Very interesting info and could be useful to anyone that has a scope and/or high end scanner or Tech 2.

A bit long but very informational.

 

m.mcmillen

Gold Supporter
Not everyone has a scanner that can command the fan clutch. I’m pretty sure that is why this method is posted.
 
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Mooseman

Mooseman

Moderator
Very good info on the function of the EV Clutch however, the quick function test requires a Tech 2. The info I posted regarding a locked clutch (beyond a few minutes) is still accurate.
 

Thunderwing

New Member
Very good info on the function of the EV Clutch however, the quick function test requires a Tech 2. The info I posted regarding a locked clutch (beyond a few minutes) is still accurate.
I think you missed the main point. (of the Tech Link, which is that a scan tool is not required if you read on)

If the goal is to determine the root cause of the issue(faulty fan clutch or the control circuit):
-unplug the fan clutch connector
-run the engine at 2000rpm for 2 minutes

The Fan Should not be roaring/fully engaged

The fan clutch should be disengaged with no voltage applied.
This applies to the complaint of 'Fan Running All of the Time'.

you said 'DO NOT TEST'.

You could have an issue with the control circuit.
It's always good to properly test and confirm a failed component before guessing and throwing parts at a complaint.

The key information in the Gm Tech Link Bulletin is that the Fan is controlled 'ON' by an electrical signal, therefore unplugging it, the fan should be 'OFF'.
 
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littleblazer

Gold Supporter
I think you missed the main point.

If the goal is to determine the root cause of the issue(faulty fan clutch or the control circuit):
-unplug the fan clutch connector
-run the engine at 2000rpm for 2 minutes

The Fan Should not be roaring/fully engaged

The fan clutch should be disengaged with no voltage applied.
This applies to the complaint of 'Fan Running All of the Time'.

you said 'DO NOT TEST'.

You could have an issue with the control circuit.
It's always good to properly test and confirm a failed component before guessing and throwing parts at a complaint.

The key information in the Gm Tech Link Bulletin is that the Fan is controlled 'ON' by an electrical signal, therefore unplugging it, the fan should be 'OFF'.
Short of a relay sticking, I see no possible cause that it would be electrical. The pwm feed is positive so if that breaks it defaults to unlocked. If the ground breaks it's the same. If you end up in full lock, the thing is somehow getting a constant positive, the pcm should see that and set a light because its command and actual are different.

And checking the relay is addressed in post 7...
 
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Mooseman

Mooseman

Moderator
When I said DO NOT TEST, that's with the method described with the rag. As you could imagine, trying to stop a locked fan with a rag would not be a pleasant experience.

And pulling the relay would have the same effect as unplugging it. And I also mention checking the wiring which is a common problem.
 

Thunderwing

New Member
Short of a relay sticking, I see no possible cause that it would be electrical. The pwm feed is positive so if that breaks it defaults to unlocked. If the ground breaks it's the same. If you end up in full lock, the thing is somehow getting a constant positive, the pcm should see that and set a light because its command and actual are different.

And checking the relay is addressed in post 7...
Electrical faults don't have to be wiring, they can be control module input/output related including:
a faulty sensor(input) giving the control module information that would make it command the fan on(output)
-wiring to one of the sensors(inputs) that as a result, affect the output of the control module
-a faulty control module

Ok, here is an example of how it could be electrical...

Complaint: 'Fan Running All of the Time'
Confirmed complaint of the fan running all of the time
Disconnected the Fan Clutch Connector at the Fan Shroud
Ran Engine at 2000rpm for 2 minutes=fan disengaged (ok)

The fault is not with the Fan Clutch as it disengaged like it is supposed to with its' connector disconnected.

The fault is within the control circuit.

Several Reasons that the fan could be commanded on including:
-A/C Command
-Coolant Temp Command
-Gearbox Oil Temp Command
-PCM Faulty
-Short-to-power
-Are there any active DTCs?

The Main point is that you want to quickly do these 2 things:
-Confirm The Complaint(and obtain as many details about the operating conditions during the time of the fault)
-Determine if the fault is mechanical or electrical(and then follow the appropriate troubleshooting steps)

In Review: The complaint is an issue with the fan clutch running all of the time(overcooling the engine cooling package). By starting diagnostics at the place in the fan clutch system where the mechanical and electrical components separate(the fan clutch connector), you successfully start the troubleshooting process in the right direction.
 

djthumper

Administrator
You do realize that you are posting things that don't work for the everyday person trying to figure out his problem. We don't all go to a dealer to get work done right away. You are also talking to people that have been doing this for a while on this platform. You should probably slow your role a little and do more reading.

I deleted all of your cross posting and starting of a new thread on this very thing. I understand you are the new kick on the forum and you think you have something to prove. So far you have proved that you just want to get into the conversations and not listen. You didn't even start with an intro thread to introduce yourself.
 

Thunderwing

New Member
You do realize that you are posting things that don't work for the everyday person trying to figure out his problem. We don't all go to a dealer to get work done right away. You are also talking to people that have been doing this for a while on this platform. You should probably slow your role a little and do more reading.

I deleted all of your cross posting and starting of a new thread on this very thing. I understand you are the new kick on the forum and you think you have something to prove. So far you have proved that you just want to get into the conversations and not listen. You didn't even start with an intro thread to introduce yourself.
I don't know what you're talking about -cross-posting and starting a new thread-
I was just trying to add some info that was missing to diag a fan running all of the time.
I didn't know I was supposed to introduce myself. I don't want to prove anything, just trying to be helpful and post that Tech link bulletin on this that I came across.
 

littleblazer

Gold Supporter
Electrical faults don't have to be wiring, they can be control module input/output related including:
a faulty sensor(input) giving the control module information that would make it command the fan on(output)
-wiring to one of the sensors(inputs) that as a result, affect the output of the control module
-a faulty control module

Ok, here is an example of how it could be electrical...

Complaint: 'Fan Running All of the Time'
Confirmed complaint of the fan running all of the time
Disconnected the Fan Clutch Connector at the Fan Shroud
Ran Engine at 2000rpm for 2 minutes=fan disengaged (ok)

The fault is not with the Fan Clutch as it disengaged like it is supposed to with its' connector disconnected.

The fault is within the control circuit.

Several Reasons that the fan could be commanded on including:
-A/C Command
-Coolant Temp Command
-Gearbox Oil Temp Command
-PCM Faulty
-Short-to-power
-Are there any active DTCs?

The Main point is that you want to quickly do these 2 things:
-Confirm The Complaint(and obtain as many details about the operating conditions during the time of the fault)
-Determine if the fault is mechanical or electrical(and then follow the appropriate troubleshooting steps)

In Review: The complaint is an issue with the fan clutch running all of the time(overcooling the engine cooling package). By starting diagnostics at the place in the fan clutch system where the mechanical and electrical components separate(the fan clutch connector), you successfully start the troubleshooting process in the right direction.
I get what you're saying, but the way the circuit is laid out, you would only get a short to power via a stuck relay. Any other command is pwm unless you are running insanely high temps. And at that point you should be more worried about destroyed components. And in the case of a faulty pcm, they brick themselves, ask me how I know...

I get the whole test it theory, but when there was a design revision preventing a lockup failure mode, you'd tend to think that is going to be (and generally is) the problem. Every electrical issue I've encountered with it is usually no feed and not the other way around. Stranger things have happened though.
 

mitchr316

New Member
Mooseman, post was a long time ago and not sure this is even active! I just joined today and been digging into whether I should replace EV on 2004 Buick Rainier 5.3. AC little warm
At idle and concerned temp climbed to 220+ a few time la pulling hills last summer when not towing. Bought a new 3k RV and picking up Saturday and want to run cool. Replaced pump and stat last year cuz dripping, assumed weep hole. Stopped dropping but a little seepage still somewhere. AC problem and heating up last year was with coolant topped off. Most of tech stuff in thread over head, but tried your fan test with rag. Seemed like stopped pretty easy other ac on and at 210 but then more forceful after tried again. What should feel like if really working good? Thank you.
 

littleblazer

Gold Supporter
Mooseman, post was a long time ago and not sure this is even active! I just joined today and been digging into whether I should replace EV on 2004 Buick Rainier 5.3. AC little warm
At idle and concerned temp climbed to 220+ a few time la pulling hills last summer when not towing. Bought a new 3k RV and picking up Saturday and want to run cool. Replaced pump and stat last year cuz dripping, assumed weep hole. Stopped dropping but a little seepage still somewhere. AC problem and heating up last year was with coolant topped off. Most of tech stuff in thread over head, but tried your fan test with rag. Seemed like stopped pretty easy other ac on and at 210 but then more forceful after tried again. What should feel like if really working good? Thank you.
Iirc if it is working properly it should try to pull out of your hand. It should spin back up instantly after you let go too.
 

mitchr316

New Member
Thank u LB. Will go feel it again. I think it’s doing what u r saying, just hard to tell how hard it should be trying to pull out of hand. Appreciate the help.
 

mitchr316

New Member
Once stopped I can hold with light pressure of single finger or thumbpad, and after revving at 2k RPM same result to stop and hold. Stopped with rag pushed in for a few minutes but couldn’t see any temp rise, with air on, but it’s 55F here.
 

MRRSM

Lifetime VIP Supporter
Time for a Radiator-Heater Core Flush? ...and... A Transmission Fluid & Cooler Lines Flush, too? Perhaps the Heat Soak cannot get carried away because things may have gotten a bit "sluggish" inside of the radiating units?

Transmission Flush:

Radiator- Heater Core Flush:
 
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Mooseman

Mooseman

Moderator
Try it again but pull the fan relay. If it feels the same, then I would assume the clutch is done. You could also put 12v+ to the white wire at the clutch (or at the relay if you can figure out which terminal it is). This should lock the clutch and pull air like a dump truck. If it doesn't change, it's toast.
 

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