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Radiator Fan Staying On When Car Off

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Old 04-20-2012, 11:19 PM   #1
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Default Radiator Fan Staying On When Car Off

I noticed that every once in a while my radiator fan will stay running after I turn the car/ignition completely off. I realized this when it killed my battery one time when I was in school for 4 hours. Now I have to unplug the fan when it stays on to avoid killing my battery again. Does this mean I should replace the fan switch?
Is that equivalent to the "thermostat switch" aka part number 37760-P00-003?

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Old 04-21-2012, 07:14 AM   #2
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Default Re: Radiator Fan Staying On When Car Off

You MUST provide all pertinent information about your car and engine. Failure to do so may result in thread closure.

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Old 04-21-2012, 08:23 AM   #3
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Default Re: Radiator Fan Staying On When Car Off

It is a 92 hatch with a B18C(R). Sorry.
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Old 04-21-2012, 09:06 AM   #4
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Default Re: Radiator Fan Staying On When Car Off

A bad radiator fan relay in the hood fuse box is a more likely cause of your problem. Test the relay.

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Old 04-21-2012, 09:39 AM   #5
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Default Re: Radiator Fan Staying On When Car Off

So I'll take out that fan relay and check to make sure there is no continuity between pins A and B. It's kind of hard to apply a voltage to the C and D terminals while checking if A is continuous with B though..
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Old 04-21-2012, 09:47 AM   #6
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Default Re: Radiator Fan Staying On When Car Off

Ok so pins A and B are discontinuous with the relay out, which is good.. But pins C and D are not completely continuous, there is about 92 ohms of resistance between them. In addition the relay does look a little burnt on the plastic enclosure and also inside right around the lead for pin B.

I think this may be the problem. Do you think that small resistance between C and D is normal? I haven't really messed with relays much so I don't if they have some impedance on those pins.

Looking at the part I see there are two part numbers and two different prices for identical parts, which one would I be better off getting?

20 39794-SE0-003 RELAY ASSY., POWER (4P) (056700-7250) (DENSO) CAN 3 $38.02 $27.56
20 39794-SL0-004 RELAY ASSY., POWER (4P) (RC-2225) (BLACK) (MITSUBA) CAN 3 $47.08 $34.13
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Old 04-21-2012, 10:07 AM   #7
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Default Re: Radiator Fan Staying On When Car Off

I think 92 Ohms for C-D may be okay. What you were most interested in is continuity for A-B without voltage applied to C-D. You didn't find that, but keep in mind that the problem is intermittent, so you may need to do the A-B test several times after applying voltage to C-D.

Wires with alligator clips at each end would allow you to apply voltage to C-D from the battery.
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Old 04-21-2012, 10:18 AM   #8
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Default Re: Radiator Fan Staying On When Car Off

Yeah true, I don't have any at home. I'd have to take some from my lab on Monday.
I agree that the they could possibly become continuous every once in a while when voltage is removed such as how my fan sometimes turns off with the car and sometimes stays on. Its only been happening for 2 days and so far its been 50/50.

I wonder what the problem could be if this is not it. For now I just unplug the fan connector when I have to leave my car parked and I can't get the fan to go off, obviously.

This burnt plastic on the relay is a little meaningful to me. This means that once there was a short between A and B when the ignition was supposed to turn everything off.
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Old 04-21-2012, 10:43 AM   #9
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Default Re: Radiator Fan Staying On When Car Off

A-B has constant voltage from the battery whereas C-D only gets voltage from the ignition switch. This is why you need to focus on A-B. Assuming that your fan wiring is stock and the relay is good, another potential cause of the problem would be bad hood fuse box. But focus on the relay first.
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Old 04-21-2012, 12:50 PM   #10
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Default Re: Radiator Fan Staying On When Car Off

Yeah the fan wiring is stock. I am using a Flex-A-Lite though, but it uses a plug and play OEM connector.
Ok I need to get some clips and do the other test.
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Old 05-02-2012, 09:15 PM   #11
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Default Re: Radiator Fan Staying On When Car Off

It's the relay.
Which one should I get, the Denso one or the Mitsuba one?

20 39794-SE0-003 RELAY ASSY., POWER (4P) (056700-7250) (DENSO) CAN 3 $38.02 $27.56
20 39794-SL0-004 RELAY ASSY., POWER (4P) (RC-2225) (BLACK) (MITSUBA) CAN 3 $47.08 $34.13
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