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?

 

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

 

It is a 92 hatch with a B18C(R). Sorry.

 

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

 

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..

 

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

 

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.

 

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.

 

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.

 

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.

 

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