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Cooling fans wont come on

58212 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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You mention that there's never any power on 85 but there is on 86. 85 and 86 are the two ends of the coil so there will be power on one side and ground on the other to complete the circuit. I'd say that 85 never having power is good, but you need to unplug each relay and ensure that 85 actually has a good ground path. It likely does, but it's such a simple test that it will only cost you time.

You have a '97 and I don't have the schematic for that, but I do have the schematic for our '08-'10 vehicles. On ours there is a third relay that switches between serial/parallel for the two fans, effectively switching them from low to high speeds. Instead of the 4-pin relays the ser/par relay has 5 pins with the extra one being a NC terminal. Here's a link to DropBox where I have the schematics. I paid $20 for them shortly after I got my car, then about a year later discovered this forum and have shared them with others.

Look on figure 18 at the top.

Temporarily, just as a stop-gap measure, can you use either a wire or resistor to jump the sensor terminals? This would serve to trick the coolant circuit into thinking that there's a constant HOT signal, forcing it to turn on the fans and maybe still drive well.

Remember, the schematics above are not for your vehicle but might help you, since they are still GM. Companies tend to keep a wiring protocol for consistency. Ford does things a little differently but they're fairly consistent year to year on how they design them. GM is the same way.
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I'm really interested in the outcome. I expect to keep my '09 till the wheels fall off (well, maybe) and it's likely that a lot of how yours is designed is still present in ours.
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