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Old 02-12-2013, 12:33 AM   #1
PixelRandy
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Question Radiator Fan comes on with Ign. Key

Hi everyone. I've tried searching for this problem and thought I'd better post the question before spending money in a desperate attempt at fixing the problem.

I have a '96 ti in great shape and has been well cared for over the years. Over the weekend, the radiator's electric fan turns in the moment you turn the key into the "On" (not start) position. It doesn't shut off until the key is turned off.

From what I've found by reading the forums, searching the 'net, etc, is that it's likely the control unit that is attached to the fan assembly. It's also not a matter of just replacing the control unit, but would require replacing the entire assembly.

Before I do that, can you please let me know if I'm heading down the right path? I'm a tinker, have a soldering iron, can still vaguely read a schematic. To me this sounds like it would be a bad really, fused in the "on" position.

I would really appreciate your insight.

Thank you! Full introduction to follow shortly in the intro section.

Cheers,

Randy
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Old 02-12-2013, 06:16 AM   #2
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My guess is that it's either a bad sensor or a bad relay...

This thread might be helpful:

http://www.318ti.org/forum/showthread.php?t=34064
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Old 02-12-2013, 09:06 PM   #3
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My guess is that it's either a bad sensor or a bad relay... This thread might be helpful: http://www.318ti.org/forum/showthread.php?t=34064
Thanks! I read through that thread. Enlightening on getting a better sense of how some of the circuits work, but it's not really applicable to my car's problem. They were having issues with the fan high/low speed settings in conjunction with the a/c, whereas mine is on whenever the ign key is turned to "on" and the a/c has no affect on it. Ha! I'm coming from a world of air-cooled Porsche's, so if the fan had trouble it meant that the belt had broken.
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Old 02-12-2013, 11:26 PM   #4
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Randy, unplug the sensor on the left of the radiator "facing the car" If the fan goes off, replace that sensor. Coolant fan temp switch.
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Old 02-12-2013, 11:58 PM   #5
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Originally Posted by poolerb View Post
Randy, unplug the sensor on the left of the radiator "facing the car" If the fan goes off, replace that sensor. Coolant fan temp switch.
Ah! I thought thermal switches typically failed in an "open" position, meaning the car would register the coolant as cold. I'll certainly try it out and will report my findings.

Thanks!

Randy
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Old 02-13-2013, 12:09 AM   #6
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well your correct, usually. but thats why if unplugging it effect it, its bad. but it prolly wont. just that niddle in the haystack often overlooked.

could also be a relay fused in open like stated ^^

what all have you tried so far?
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Old 02-13-2013, 12:34 AM   #7
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Originally Posted by poolerb View Post
what all have you tried so far?
I've been reluctant to try chase ghosts until I researched the symptom and made my post here. I thought it may have been a common problem.

I'll start with the thermal sensor.

If it is the relay, then is it true that I may need to replace the entire fan assembly as it's not a plug-in relay? Have others gotten around this by soldering in a replacement?

Thanks!
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Old 02-13-2013, 02:06 AM   #8
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Quote:
Originally Posted by PixelRandy View Post
Ah! I thought thermal switches typically failed in an "open" position, meaning the car would register the coolant as cold. I'll certainly try it out and will report my findings.

Thanks!

Randy

The fan temp switch and the temp sensor to the instrument cluster are two different sensors. The fan sensor is a larger, brass sensor screwed into the passenger side tank of the radiator, the instrument sensor is a smaller brass sensor screwed into the cylinder head just underneath the intake manifold.

Start by unplugging that sensor and if there's no change, move to the fan relays (I realize the previous link I posted was not exactly the issue you were experiencing, but the information on relays and their location is pertinent here). It sounds to my like it's one or the other.
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Old 02-14-2013, 01:58 AM   #9
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ive never heard of the relay built in, Randy. the purple one in the row of 3 with 2 yellow, is the high speed. the other two yellow are your low speed, and ac compresser.
switch the two yellow, and pull the purp. any change?
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