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Cooling fans wont come on

58214 Views 19 Replies 6 Participants Last post by  ryan22soy
I'm working on my son's Malibu. It's a 97, 3.1L, auto, 125,000 miles.

The thermostat is opening when it should, the water pump is pushing water, the coolant temp sensor was just replaced and has proper Ohm reading at cold and hot temps. All fuses are good and all relays test good too. The fans come on if I unplug the coolant temp sensor (although the car runs like crap with it unplugged) If I jump the Fan 1(location #12 on the fuse box) relay with a fused jumper wire from pin 30 to 87 both fans come on (seems like low speed). If I jump fan 2 (Location 14) from pin 30 to 87 passenger fan comes on (seems like high speed).

So the temp sensor works, all the fuses and all the relays are good, and the fans themselves work as well.

When I turn AC on and blower on high the fans do not come on. But that may be because previous owner removed compressor and put in an AC bypass pulley. Not sure about that...

Haynes says where the relays plug in the fuse box I should have constant power to pin 30. And I should have power to pin 85 w/key on. I do have power at both pin 30's, but don't get power to pin 85 with the key on, with engine running, or with engine running above normal op temp.

I do however have power to pin 86 for fan 1 with car on or off, and I do have power to pin 86 and 87 on fan 2 with car on or off. Which doesn't seem right.

Extra info, it has a new expansion tank cap, system is 50/50 coolant water, all air has been bleed out through the bleeder valve. Has good vacuum, good fuel pressure, full oil (not milky) do not suspect head gasket or lower intake manifold gasket. No coolant leaks either.

From the beginning of the overheating story: the car was overheating and overflowing from under the cap, my son kept adding water/coolant but never bled the air out. It kept getting hot, (never got to red because I told him these cars blow gaskets easy and to just pull over) The cap was bad so we bought a new one, refilled and bled the air out. Then the car held temp right at 1/2 line or just above at red lights. Indicating a fan issue. Since fans came on with sensor unplugged and relays and fuses tested good, we put in a new temp sensor. But still no fans. That's when I started rechecking relays and power at the pin locations in the fuse box and got some odd reading that didn't add up.

I'm really hoping there is something else that would cause this besides the PCM, is there anything else I can test, try, replace, etc besides the PCM? Is there another sensor besides the coolant temp, fuse, or relay besides what's in the under hood fuse box that might be keeping these fans from switching on?

Thanks in advance, I've already check everything the haynes manual says to check, but it doesn't say what to do if pin 85 doesn't have power with key on. I've read lots of overheating threads online and seems like most or from loosing coolant, not bleeding air out, bad relays or bad fans. I have none of that and am kinda stuck. Thanks in advance for any help/ideas!
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New to the forum and I am having the EXACT same problem with my 99 Malibu. It sucks that this thread didn't come to a better resolution than to sell the car! I have no power to pin 85 on my relay and the only diagram I've seen anywhere on here that says where pin 85 gets its power from says it comes from "Power Distribution Cell 10". Which I have no idea where that would be. I'm going to pull the thermo switch connector, since it makes the fans come on, and check pin 85 again. This will tell me if its the PCM kicking the fans on or some redundant failsafe from elsewhere. Will post back on this thread tomorrow with results. If anyone out there has the fix for this I would love to know before I break down and get an aftermarket fan controller.
Thanks for the diagrams. Sorry about the confusing dialogue. I was referring to the different pins on the actual relay. What you're saying is correct in that the powered side of the relay is pin 86 and the grounded side (controlled by the PCM) is 85. The Haynes manual has this information wrong. So that having been figured out the hardest of ways, I have no fault codes and I have power to all the correct pins. The fan was jammed due to a collision at the bottom of the car and the fuse was blown. I've jumperwired the relays and have gotten the fans to work. I've also gotten them to turn on by pulling the wires to the coolant temp sensor (which I have replaced). So I am convinced its either a software problem, or this quad driver module you speak of. Can you tell me what a quad driver module is and if i can replace it?

I see. Well from all the information I've been able to collect and with the troubleshooting I've done, combined with what your telling me about how sensitive these QDM's are to current overflow, I am almost positive that I have a PCM problem. I will get the car scanned for any codes it may have stored, but since I've worked on it alot recently there may not be any due to removing the battery cables. Here is the thing. It cost $99 to get it looked at at chevy. The PCM is only $120 flashed and ready to install. If I get the fault code when I scan, I will forgo the diagnostic and just replace the PCM. I would hate to give them $99 just to have them tell me to replace it anyway. When I called them they told me that it could very well be the PCM so I'd rather gamble on the chance to save money. :) My goal is to end this post with a solution to this problem so others can save money and all the hassle I've been through trying to get this fixed.
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