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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.
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Tedybear315, here is a schematic I found online It’s
different than my Haynes manual layout, but appears to be accurate.
It seems this one is on track. I’ll only add that I’ve written extensively about solving electrical issues in this article that you might find helpful.
http://www.ericthecarguy.com/faq/solving-automotive-electrical-problems
Please continue to keep us updated on your progress.
3 relays for 2 cooling fans.
Quite interesting. How is the relay #2 working? Cooling fan #1 is coming on…so relay #1 is working…Relay #2? That one determines if fan #1 is on full power—or goes in ‘Series’ with fan #2.
Cooling fan #1 relay: Just does #1 fan.
Cooling fan relay: Controls if the fan #1 is on full power—or “shunted” (for lack of a better word) through fan #2.
Cooling fan #2 relay: Determines if #2 fan comes on at full power.
Interesting setup. 1 fan on at full power. Both fans on at 1/2 power. Or both fans on at full power.
When fan #1 comes on. Does it come on ‘Full Force’? Or does it come on kinda wimpy? Like it’s on 1/2 way power.
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Well Tedybear315, it’s hard to tell whether fan 1is on full or half power. The motor is smaller than fan 2 motor. Also, it sits lower on the fan assembly than number 2. I would guess full power.
So, with the light blue wire bypassed and controlled by a switch to positive on number 2, fan number 1 still comes on in sequence with the ac compressor. I hated to rig it up, but my wife needs the van and it would otherwise overheat in traffic.
This post is getting long so you may not have read..I swapped out all 3 solenoids. I swapped out the fan wiring harness as well even though I had checked the original for continuity. The same symptoms persisted with fan number two. It only fired up when I jumped the positive to 12 volts. Crazy, huh?
It’s a unique issue that’s for sure.
The connections where the relays plug into the box–are they nice and tight? Any signs of heat warping or melted plastic?
There has to be something simple and stupid everyone (including myself) is overlooking.
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The more I think about this, I lean towards barnyb’s suggestion that this might be a good voltage/poor amperage issue…
like a severed wire holding on by a strand for example.
everything will test good… voltage.. continuity… and you just end up scratching your head and wondering why won’t anything work.. until you find out that you are not getting good current.. and amperage is usually the toughest thing to test because with cheap multi-meters you’d have to actually connect the ammeter in series with the circuit.. effectively making your meter part of the circuit. on top of that, most cheap multi-meters can only read up to 10 amps before frying the meter.
[quote=”Ratchet Face” post=110435]The more I think about this, I lean towards barnyb’s suggestion that it might be a good voltage/poor amperage issue.[/quote]
That’s what I’m leaning to. Hence asking about the condition of the relay box and the ‘lugs’ the relay goes into. Oxidation and burnt connections can show voltage where it needs to be–but get under the actual load of the fan? The current flow will crap out and you’ll have zippola to turn the fans.
Heck, a can of electronic solvent from WalMart or an auto parts house..and a hook scribe to tighten the connections might be all it needs.
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Thanks Ratchetface and Tedybear315. At least by this point I don’t feel totally stupid…lol
I’ve attached a picture of the type of external fuse panel used on this make. Everything on the top side looks good (no signs of warpage or heat at any of the connectors). I don’t know how to get this guy open to look at the bottom where the wires adjoin, but will figure that out.Based on logical sequence from the wiring diagram and the symptoms described, wouldn’t you guys agree that the PCM is an unlikely cause? With fan number 1 coming on (when fan number 2 should at the same time) wouldn’t that mean the first calling signal from the PCM is working?
I run into the strangest things…when you have time, check out one of my previous posts GM 3400 mystery misfire.
Thanks again for you interest and time.
You may not have to remove the fuse box to check the wiring. In fact, I wouldn’t recommend it because it’s really not necessary. All you need to know is what terminal goes where and you can use an ohm meter to check the wiring. Normally with relays the larger terminals are the load, the smaller terminals are often the control. You might try ‘wiggling’ the relays while the fan is suppose to be in operation. If you see a reaction at the fan then perhaps it is a connection issue at the relay. If that’s the case, you might consider bending the relay terminals slightly to make better contact. I’ve done this on a couple of occasions. You don’t have to bend them a lot, just enough to make a better connection.
Keep us posted.
Okay.
Cooling fan control circuit #1. Kicks ‘on’ engages cooling fan relay #1 and the smaller of the two fans (#1) kicks on at 1/2 power, and fan #2 should also kick ‘on’ at 1/2 power as well.
That is due to the wiring of the ‘center’ fan relay. That relay in it’s ‘rest’ state has the ground line from the fan #1 going to the positive fan lead of #2 fan. It runs both in series.
Enter fan control circuit #2. That line goes to ground, and it kicks BOTH #2 relay and #3 relay. This removes the fans being run in ‘Series’ at 1/2 power. It kicks fan #1 to full power by kicking that wire to ground off from relay #2. The Relay #3? That puts full voltage to fan #2.
If you ground F3 (not the fuse—the part of the harness labeled “F3” on your diagram.) That should kick the relay ‘on’ (you should feel/hear it click) Both fans should be running at 1/2 speed.
Likewise if you ground C10. That should kick both the ‘Fan Relay’ and Fan Relay #2 to the ‘on’ state. Now if you ground both F3—and C10? Then both fans should run great guns!
Only ground C10? And you’ll only have the 2nd cooling fan running.
I’m left to wonder if you might not be thinking fan #1 and #2 in the correct relationship. If only the C10 line and it’s respective to relays are functional–Then you will only have one fan spinning. That would be the #2 fan.
The only way both fans will spin, depends on Relay #1. Relay #1 on….other two relays ‘off’ Then both fans spin at 1/2 power. All 3 relays ‘on’? And you’ll have both fans spinning full speed. Relay #1 ‘off’ and other two “On”? Then you’ll have the #2 fan spinning at full speed…fan #1 off.
Make sense? Just trying to get a grip on it.
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Tedybear315, you are one patient man to type all of this out. Thank you very much. Yes, this makes sense to me. I will update this forum in the not too distant future. I know how frustrating it can be to walk with someone through an issue, only to have them never tell how something turned out or go MIA. I have a couple other car repairs waiting on me over the next few weekends. This involves a timing belt job on one and a seized ac compressor on another. So, this issue will need to rest for a while, but I will update it. Thanks to all who contributed to this. Thank you Eric for creating this forum.
Quite all right. I work full time as an electronics tech/repair/manager for a video arcade. I got lucky the last couple of days off and had the time off to dig into things and hopefully lend any direction that might be helpful.
I’m subscribed to this topic, and look forward to seeing how things turn out. It’s quite interesting.
One thing that might prove interesting. I believe you can use a test light to verify the signal from the ECU-Power train module..whatever that want to call it that controls the signal. 1/2 of that circuit is 12vdc via the fuse. The computer control grounds the signal. Soooo….Use a test light with the ground clip on the positive—Insert the probe into the relay socket that feeds the ground signal. Now if all things being equal–If you turn on the A/C? It should flag all 3 relays to kick ‘on’. (Okay…So it will send 2 signals. One for ‘fan 1’ and one that splits and feeds fan2 and fanrelay) So the test light should “Light”. If the computer is grounding those lines? That light should kick ‘on’ by command.
Just an idea. I think either Eric or ScannerDanner did some basic instruction on this test procedure.
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That’s the quick and dirty way to see if the computer is sending the ground signal
To those following this post, this mystery may be unraveling. Those who guessed a voltage but deficient amperage issue were likely right on… I finally got my hands back on the van tonight after my wife returned. I popped the bottom off the auxiliary fuse/ relay box and found the infamous blue wire that powers fan #2. The insulation was dark and discolored near the connector. Also, when examining the connector from the top (under the relay), I saw melted plastic. Nothing at all was apparent from the top. It’s late here on the East Coast, so I’ll get after this tomorrow and follow up. Here are a couple pictures. Note, I’m pointing to the suspected wire in one of them.
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