Engine Coolant Fan Outsmarting Me

[Glenn]

Being able to understand wiring diagrams and troubleshoot wiring often separates the men from the boys (or, not dissing the ladies, the “real mechanics from the wannabes”). So, I confess, I’m a boy on this one. The vehicle is an ’02 Chevy Venture LS with front wheel drive 3.4L engine.

Coolant fan number 2 (passenger side facing vehicle) stopped working. With our hot Southern summers and a salvage yard nearby, I went and bought another fan without attempting any diagnostics. I discovered the issue is not the fan. Number 2 cooling fan will not come on. Here is what I know:

The cooling fan (salvage and original are good) This was determined by testing fans off the car, and using the connector for cooling fan 1.
I checked the fan wiring harness for continuity (pictured at bottom), all is good.

With my multimeter, I verified I have good current going to the motor (light blue wire) and coming from the motor, black.
Both relays are fine, I swapped them.
Both 30 amp maxi fuses are fine.
The ac clutch relay seems to work, it turns on the number 1 fan when ac is turned on.
My tests were performed with the vehicle cranked and the ac turned on…

I’ve used a bypass wire from coolant fan number 2 black at the fan and grounded it. Still the fan will not work. I’m scratching me head here. With proper voltage going to the fan and grounding the return it still will not turn on.

I’ve attached a few photos, including a wiring diagram. Maybe you can see it without it being too blurry. Please be gentle if I’ve colored something wrong. Staying dirty and learning.

Attachments:

• image_2014-09-01.jpg
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Topic

[Joeseph Mama]

Jump 87 and 30 and see if your fan comes on.

IF it does come on, we can rule out a “load side” problem. In this case I would lean towards wysetech’s suggestion of a signal problem (possibly with the PCM) in which case a bi-directional scan tool will be needed for further diagnosis.

Test the circuit for continuity before condemning the PCM.

[Glenn]

Thanks Wysetech…Correct me if I’m wrong. The PCM commands current to the relay, the relay then switches upon command, sending positive current to the fan. Since I have voltage at the fan, should I at least assume the PCM is doing it’s part?

[Joeseph Mama]

Since I have voltage at the fan, should I at least assume the PCM is doing it’s part?

This piece of information may imply that you have a problem in the ground circuit.

Apply your own ground to the #2 fan motor and see if your fan operates normally…

[Glenn]

Ratchetface,jumping 87 and 30 didn’t work either this disabled both fans . Did anybody take a peek at the wiring diagram in the original post? I appreciate all you guys commenting. I’m off to buy wire and a switch so my wife can drive tomorrow.

[Glenn]

I did apply my own ground… It didn’t work. I was thinking ground originally.

[Joeseph Mama]

So to recap:

You’ve applied power to the fan and it works.

You’ve jumped 87 & 30 and the fan doesn’t work.

You get 12v power to the fan.

Applying your own ground to the fan motor has no effect.

Q: are all the above statements true…

[Glenn]

Yes..true

[Bryan Carter]

In your initial post you stated:

[quote=”tomatofarmer1″ post=110148]
With my multimeter, I verified I have good current going to the motor (light blue wire) and coming from the motor, black.[/quote]
So, what was that current reading? How many amps did you see?

[Glenn]

Well, here I have to confess to McWicked…what an oxymoron 🙂 As a weekend warrior, my diagnostic tools aren’t the greatest. I have a simple multimeter that only shows volts, not amps. I need to get serious and buy a better multimeter. The blue wire in question is a 10 gauge wire, not one to easily get stressed and broken. Don’t kick me out of the club, here is my temporary fix idea until I can obtain equipment to go deeper. See the toggle switch. Gotta keep the wheels rollin’.

Attachments:

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[Joeseph Mama]

you’ve stated that the following conditions are true:

You get 12v power to the fan.

Applying your own ground to the fan motor has no effect.

You have a bad fan motor.

Remove & replace.

but…

this contradicts another statement you said was true…

You’ve applied power to the fan and it works.

Because of this confusion, I am not sure where to go from here.

[Glenn]

Yes it does appear to be contradictory unless what Barneyb says is true. This thing drove me nuts. I really hate to MvGyver rig something up. I appreciate your input even though I didn’t get it sorted out. Thank you.

[Bryan Carter]

[quote=”tomatofarmer1″ post=110237]Well, here I have to confess to McWicked… I have a simple multimeter that only shows volts, not amps.[/quote]
Yeah… most simple meters can’t read amperage. Even many excellent meters can’t handle the amp load of a fan circuit. That’s one of the reasons I was surprised by your claim of having read “good current”. The other reason I was surprised was the fact that you were seeing current run through a non-functional circuit. That’s why I asked what the reading was…

[Bryan Kamphus]

Just out of the blue have you check the switch that controls the fans? AKA Temp switch? maybe a bad switch and the one fan staying on is just a default setting you say the fans work and they both get supplied power so im leaning toward the temp switch (Not the temp sensor)

Not a mechanic but seems legit

[Stephen Bowen]

[quote=”tomatofarmer1″ post=110208]Ratchetface,jumping 87 and 30 didn’t work either this disabled both fans . Did anybody take a peek at the wiring diagram in the original post? I appreciate all you guys commenting. I’m off to buy wire and a switch so my wife can drive tomorrow.[/quote]

Any chance you can get a scan or PDF of that wiring diagram? I tried to read it but my eyes are not what they used to be.

S-

[Randy]

First post here, but this is a great site for troubleshooting!

What you’re missing in your troubleshooting verbiage is that the Fan 2 should also be coming on with Fan 1 in the first cooling call (via ECM signal “DK GRN”), and they both should run at half speed (approx.), since they are wired in series at that point. You can run in series with DC motors, plus it gives full face flow across the radiator coil.

I’d back up and re-test the inputs/outputs for Fan 1 with just Fan 1 ECM call on. Fan 1 will NOT have a direct ground at that point.

Second cooling call (via EMC signal “DK BLU”), runs both fans at high speed with full 12 volt to both, and gives the Fan 1 a true ground. Probably why you got the strange readings on your voltmeter.

[Author]

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