Engine Fans Stay On (FIXED) - GM Forum - Buick, Cadillac, Chev, Olds, GMC & Pontiac chat


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Old 07-22-2007, 10:51 PM   #1
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Default Engine Fans Stay On (FIXED)

I just noticed that both engine fans are running even when car is not really hot. Usually they are off. I hook up scanner and get no codes and coolant temp reads 195. It states a/c off, a/c clutch off but high head pressure. I suspect this is why it is on. A/c is not operable. I replaced compressor last year but never got it evacuated and recharged. Compressor wire connector is disconnected. It has been like this for 8 months and now I'm getting high head pressure (which I believe to be the cause of the fans on). What would cause the fans to stay on? Is there something else I need to look at?
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Old 07-23-2007, 08:22 PM   #2
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This thread seems be getting buried. I know the fans are controlled by PCM and they shouldn't be on. The fans go off when the ignition is off, thank god. They go on with ignition in the on position and they seem to be running on high.
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Old 07-23-2007, 08:34 PM   #3
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Do you have a meter you can use to check the fan relays?
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Old 07-23-2007, 10:18 PM   #4
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Quote:
Originally Posted by Technical Ted
Do you have a meter you can use to check the fan relays?

Yes I do. How would I test them and where are they exactly? I know they are on the firewall under the hood but they are not labeled.
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Old 07-23-2007, 11:14 PM   #5
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Here'* a diagram showing the location of the underhood relays. Before we check relays have you tried unplugging the A/C pressure switch?

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Old 07-24-2007, 09:22 AM   #6
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Are the fans being commanded on by the pcm?
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Old 07-24-2007, 10:38 AM   #7
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Quote:
Originally Posted by BillBoost37
Are the fans being commanded on by the pcm?
That is my concern. When I did the scan I saw a/c request off, a/c clutch off but head pressure said high. Also it stated that fan relay 1 and 2 were "requested". I depressed the schrader value and got a little air/gas out but I still have high head pressure. Where is the a/c pressure switch? Is that the one on the drier?

I have already reset the pcm by disconnecting the battery for a while twice and no change.
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Old 07-24-2007, 10:46 AM   #8
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Well.. see there'* nothing here to indicate that you need to look over the AC system. Let'* move you away from the AC for a moment and talk a few other things.

The fans are on because the pcm is requesting it. Ok.. now why? You had the AC like this for quite some time from the sounds of it w/o any issues. I'm then thinking..what else can turn them on.

Have you looked at the temp according to the scan tool? You have two temp sensors..one for the pcm and one for the gauge on the dash. If your pcm one failed..it might be defaulting the fans on.
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Old 07-24-2007, 11:54 AM   #9
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Make sure your temp gauge is functioning..if it is unplugged the fans will automatically turn on.
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Old 07-24-2007, 11:54 AM   #10
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Quote:
Originally Posted by BillBoost37
Have you looked at the temp according to the scan tool? You have two temp sensors..one for the pcm and one for the gauge on the dash. If your pcm one failed..it might be defaulting the fans on.
Last week when I initially found the problem the scan tool said coolant temp was 195. The gauge on the dash was similar. A few weeks back when I had a misfire I noticed head pressure listed as normal, which I believe is the only other reading under head pressure. I suspect the pcm is going wacky.

I have another pcm that I had taken out 6 months ago as I was having some severe problems and suspected pcm was bad. Swapped with another one and problem didn't go away, so I think the old pcm is ok. I'll swap that out again and see if things change.
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