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Old 05-08-2011, 06:42 PM
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99' Montana Coooling Fan Issue

I have a 99 Pontiac Montana Miniature Van that the cooling fans will not turn on. I can turn the fans on with my snap on scanner and they will run all day long but they will not turn on otherwise when needed, any ideas?

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Old 05-08-2011, 07:41 PM
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How warm did it get?
Sounds like a defective PCM or software.It should turn the fans on by the time it hits 232-235.
If it doesnt turn them on (you should have a fan request status in the live data stream to view as well as temperature)and the scanner runs them , you have a pcm problem.
I dont usually take the time to warm up the engine to check, I have a CTS handy for most GMs . I just plug it in to the harness, turn on the key, watch the live data and heat the cts with a lighter,whenit hits the proper temp it should kick the fans on, if not at least the engine isnt to hot to work on and you didnt have to waste ten to fifteen minutes messing with it to warm it up.

Last edited by latech; 05-08-2011 at 07:47 PM.
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Old 05-08-2011, 07:41 PM
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Does it overheat? You might try a different fan-stat, they are cheap. Or take yours out and put it in a pan of water with a thermostat and heat it up to see where it closes. All GMs used to close at 108C which is around 232F so they have to be pretty hot, not sure if yours is the same but chances are it is. Also try turning on the a/c, that should cycle the fans too.
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Old 05-08-2011, 07:51 PM
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the fans are controlled bythe computer VIA the coolant temp sensor and the read only memory part of the eeprom. Not by a switch that "Closes " at a certain temp.When the CTS (thermistor) get s to a certain ohms value the PCM sees that and whatever value is programmed into the eeprom is what it sees as the fan request temp.
The software could be corrupted, but more likeley the eeprom is bad and not controlling the quad driver that runs the fan relay coil circuit.
The AC switch is another way to check if the fan will run but it checks the output part of the pcm for the ac request and the quad driver. It too is not controlled by a switch per se anymore.There are pressure sensors doing the work to increase efficiency.It still wont verify the coolant temp request for fans.
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Old 05-09-2011, 05:09 PM
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I messed with it a little more tonight, I got the vehicle up to around 210 and the fans didn't kick on, I unplugged the temp sensor and the fans kicked on but they just continued to run for like 10-15 minutes then I plugged the sensor back on and they kicked off within 15 seconds??
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Old 05-09-2011, 05:20 PM
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the sensor wont kick the fans untill a least 220 or a little higher.
In the past I have had very bad luck with aftermarket coolant sensors for the montana and the venture, so if you replace it use a delphi or ac delco.
There are 3 pins in the sensor , not 2.
Like i said the easiest way to check if the fans are working is to heat a sensor with a lighter while watching the live data, you dont even need to have the car running, just have the ignition on and watch the data stream pid for the coolant, heat it with a lighter and note the temps when the fan kicks on. So easy.You cant do it with the sensor in the engine(obviously)
Like I said I have had A LOT OF TROUBLE with aftermarket sensors on these so dont replace it unless you use a delphi or ac delco. Trust me.
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Old 05-09-2011, 05:20 PM
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looking at my haynes manual it is telling me that at 32 degrees the resistance in ohms should be around 9420 ohms and at 212 degrees it is telling me the resistance should be a 176 ohms, so when I unplug the sensor it is telling the pcm 0 ohms, correct? So then it kicks the fans on because there is no resistance? I replaced the sensor about a month ago and it didn't take care of the problem, I just got back on this project a couple of days ago. So maybe I just got a bad sensor?
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Old 05-09-2011, 05:24 PM
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Quote:
Originally Posted by crussell85
looking at my haynes manual it is telling me that at 32 degrees the resistance in ohms should be around 9420 ohms and at 212 degrees it is telling me the resistance should be a 176 ohms, so when I unplug the sensor it is telling the pcm 0 ohms, correct? So then it kicks the fans on because there is no resistance? I replaced the sensor about a month ago and it didn't take care of the problem, I just got back on this project a couple of days ago. So maybe I just got a bad sensor?
No , an open circuit is infinite, ( hi resistance) but this is a 3 wire sensor and a circuit fault like unplugging it is probably a redundant feature that trips the fans. 0 ohms would be a closed circuit not an open circuit.
Like I said about the aftermarket sensors..........
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Old 05-09-2011, 05:27 PM
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are you saying the manual is wrong then? If 176ohms is read at 212 degrees?

If the fans are running when I unplug the sensor does that rule out the pcm? Should I replace the sensor with a delphi or ac, and go from there?
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Old 05-09-2011, 05:41 PM
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Quote:
Originally Posted by crussell85
are you saying the manual is wrong then? If 176ohms is read at 212 degrees?

If the fans are running when I unplug the sensor does that rule out the pcm? Should I replace the sensor with a delphi or ac, and go from there?
I dont have the specs in front of me as I am not at the shop,but when warm a hundred ohms could be a pretty big jump in temp as far as switching the fans on and off. I would use a gm sensor and see what happens.
Also the fans arent usually set to turn on untill untill 225 or more, so wait and watch to see how hot it gets and check temps at the coolant sensor with an infrared thermometer to be sure you are within about 2 degrees.
225 on temp is not out of line at all, in fact 230 is considered normal for most cars.
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