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
• image_2014-09-01-4.jpg
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Topic

[Glenn]

Okay, a little update…I understand if nobody touches this… The ground seems to be good coming from the black wire. Using jumper wires I jumped from fan motor terminal ground (black) to fan connector black. I bypassed the light blue wire at the connector and went straight to the battery positive. The fan came on…Unless my multimeter is wacky, it’s still showing 12+ volts at the blue wire connector at the motor terminal… Haha…Any brave souls? :cheer:

[Joeseph Mama]

I understand if nobody touches this…

This isn’t rocket surgery; any qualified technician here can handle a cooling fan problem.

I’ve used a bypass wire from coolant fan number 2 black at the fan and grounded it. Still the fan will not work.

If you’ve supplied power and ground directly to fan #2 and it is still inop, replace fan #2.

[Glenn]

Thanks, I know it’s confusing. I jumped/bypassed positive and it came on. Confusing thing is, multimeter showed 12+ volts all the way to fan from terminal connector.

[Joeseph Mama]

Thanks, I know it’s confusing.

This is easy.

So, you’ve determined that your #2 fan can actually work, now it’s time to do some testing.

The next easiest step is to test some of the major players involved in your cooling fan circuit. Probably the easiest thing to check at this point would be the #3 (high speed fan) relay. You could actually take the time and effort to learn how to test this relay… or you could just swap it out with a known good relay. (the horn relay for example.)

In the meantime, you might want check out this recent (and very similar) case study:

http://www.ericthecarguy.com/kunena/8-Service-and-Repair-Questions-Answered-Here/52585-05-impala-cooling-fan-issue

[Glenn]

Swapped out all relays, coolant fan 1, coolant fan 2 and the 3rd relay simply
Iabeled coolant fan relay (all 3 are pictured in the wiring diagram picture from original post). Fan still only comes on when jumped to battery (light blue) hot wire. I’m glad this is easy, but I’ve spent many hours now and I’m stumped. :dry:

[Joeseph Mama]

Pull the #3 relay. Now using a paper clip, ‘jump’ the relay socket at terminals 30 and 87 in an attempt to ‘force’ your #2 fan to work.

Your relay may or may not match this picture; but it will give you the idea… most relays have the pins numbered on the relay itself; use this as a guide to show where to actually apply the jumper.

Attachments:

• isorelay.jpg

[Mike Chose]

If I understand correctly, if you apply your own 12v from battery the fan works, if the measure the wiring harness that supplies the fan with power the meter reads 12v?

[Joeseph Mama]

if the measure the wiring harness that supplies the fan with power the meter reads 12v?

could someone translate this for me please.

Perform the aforementioned jumper test in order to identify and isolate the fault as being either on the “signal (control)” or “load” side of the circuit.

Report your results back to this forum.

Q: Just out of curiosity, does your A/C compressor clutch engage? (Do you hear a ‘clunk’ when you turn on your a/c or does your a/c blow cold)

[Glenn]

Correct unless my multimeter is whacked…

[Mike Chose]

Sounded like he was reading 12v to the connector the powers the fan

[Bill]

You really need a bidirectional scan tool to see if both fans are being commanded on by the PCM. If not you can command them on with the scan tool. Reason I suggest this is cuz we just had a similar van in our shop with a cooling fan problem. Turned out to be the PCM.

[Glenn]

Don’t know if you can zoom in on this pick of relay 3. Jumped the wires between 87 and 87a .
Neither fan came on…May have to hot wire the fan. The car has to roll tomorrow..thanks for your patience here.

Attachments:

• image_2014-09-01-2.jpg

[Lorrin Barth]

Also, just because you can read 12V at the fan doesn’t mean there is power there. Power is voltage x current. A bad connection may (and often does) provide you voltage but no current.

[Mike Chose]

Don’t think it is the meter. I would measure the AMP from the connector, maybe not enough current to drive fan, or the fan motor has to much resistance. You could OHM out to check. Compare with another or else it might be in line with what wysetech said

[Glenn]

Yes to both of these questions. The a compressor clutch engages, and it’s cold…

[Author]

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