cooling fans won't run. 99 grand prix 3.8 - GM Forum - Buick, Cadillac, Chev, Olds, GMC & Pontiac chat


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Old 05-03-2014, 06:04 PM   #1
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Default cooling fans won't run. 99 grand prix 3.8

replaced ect sensor, fuses are good, relays are good, no power at connection for fans
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Old 05-03-2014, 06:26 PM   #2
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At what temp are you expecting them to come on?
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Old 05-03-2014, 07:01 PM   #3
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temp almost redlines then I shut it down
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Old 05-04-2014, 10:55 AM   #4
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two maxi fuses cooling fan 1 and 2 and three relays cool fan, cool fan 1 and cool fan 2, check all for being blown or loose or corroded sockets, check the fuses with a meter to see if they are getting power.
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Old 05-04-2014, 01:54 PM   #5
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everything appears fine but the only way I can get a fan to work is if I take out the cooling fan relay(5 prong) and with a test light attached to battery ground and insert probe into lower left side socket.
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Old 05-04-2014, 07:04 PM   #6
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with car running, tested all wires at the fan. all 4 wires showed as being ground. unplugged NEW ect sensor while car was running now I have high speed fans. is sensor faulty or dig some more
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Old 05-04-2014, 07:32 PM   #7
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If you disconnect the ECT sensor and the fans turn on, then this is normal. Its designed to do this.

Is there any way you can get a live data scanner hooked up to see the actual temperature of what the PCM is seeing?
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Old 05-04-2014, 09:29 PM   #8
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I have a code reader. will that do?
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Old 05-04-2014, 11:09 PM   #9
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What make,model is the code reader?
Some will show you live data, some won't.
If it shows coolant temperature somewhere while hooked up, then that will do.
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Old 05-05-2014, 08:12 AM   #10
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you know everything from the pcm is good if the unplugging the ect makes them turn on, maybe bad new ect. like they said need live data scanner to be sure what the pcm is seeing

if your a/c is working you should have seen the fans some on when you turn it on. i think unless it has some limit tied to engine temp. i know if the a/c is discharged it will not work
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