Cooling fan in my 99 Civic EX is not working. Tried replacing the sensor which did not fix it. So I took a wire a jumped it across the contacts on the connector and the fan comes on.

What am I missing? Both old and new sender are bad? I bought the new one at Auto Zone. Thermostat has been replaced, and engine temperature behaves normally until I stop at a long red light.

Any ideas are greatly appreciated.

 

welcome to the forum. possible fan relay, if the sensors are good.

 

That would be my guess,bad relay.

 

Thanks for the replies.

First, a correction -- the Civic is a 2002 not a 1999. Sorry.

After the switch replacement didn't solve the problem I used a wire to jump across the terminals on the switch connector and viola! -- Relay goes click and fan comes on.

So, mystery still remains -- why doesn't fan turn on (unless I jump switch with wire)?

I'm starting to think I have a headgasket leak. At first I thought I had air in the system and that was why I was having to add coolant but I'm beginning to wonder. Maybe low fluid level is causing a situation where sensor switch is not being heated properly? Top radiator hose gets hard when system is hot so I'm building up pressure. I've pulled the spark plugs and don't see any water staining and I don't see any water in my oil. When I get a chance I think I'm going to do a leakdown test.

 

Hi, I have a 03 honda civic ex 1.7l I was wondering if you found a solution for this issue? Was it the radiator fan switch? I have the same issue my radiator fan doesnt come on and my relay is fine and the fan does work if i short the connector. I have purchased 2 fan switches from autozone and nothings changed. I have also done a block check on my honda and tested the thermostat both seem to be fine. How do i test the fan switch? is it possible all 3 switches are bad (2 new from autozone)? Can i just boil a pot of water and dip the switch in it with a ohm meter and see if it closes? Any help would be nice.
Thanks

 

Short answer, no.

I should point out my Civic is an '02, not a '99.

When I short out the contacts in the connector my fan comes on as well. As long as I don't get caught in stop/go traffic on a hot day the cooling system behaves normally.

I'm beginning to wonder if I don't have two bad fan switches as well, the original Honda unit, and the Autozone unit I replaced it with. When I get a chance I will try putting the switch in boiling water with an ohm meter. I think the hard part will be connecting to the small pins.

I've done a block test, a compression test and a leakdown test. Nothing seems to indicate I have a bad head gasket.

 

Good news - I believe my car is fixed.

What I believe fixed it -- After a lot of trial and error filled my radiator and accidentally overfilled my overflow tank. I took the car out for a drive. No, overheating issues, but it wasn't particularly hot out. When I got back I popped the hood and it was clear the overflow tank had blown a lot of coolant in the engine compartment which was no suprise. Top radiator hose was firm. Waited for engine to cool a bit and removed the radiator cap and there was no coolant in the top tank of the radiator. Could see it in the tubes. Coolant was at least 2" low. Read a little about radiator caps and decided to replace mine. New OEM radiator cap put on today and I drove around in some hot weather. Temperature gauge read normal even in stop/go traffic. Too loud out to hear if fans running. Pulled into driveway and left engine to idle. Shortly afterward heard cooling fan kick in. Ran for about 30 seconds and then stopped. Wait couple of minutes and fans kick in again and cycle off shortly afterward. Waited for a few of these cycles and things look good now.

 

I have the same problem with the fans not coming on. I tried jumping the switch with a paperclip and the fans started right up. I put a new switch in and it didn't work. Since then and too late I saw video that said not to insert the paperclip because it can spread the contacts out to the point where they don't contact the new switch. It also possible that the new switch is faulty and I've ordered new Honda one. What happens if I just leave the paperclip in and let the fans run all the time?

 

To check the sensor, you need to know the dependence of its resistance on temperature. Yes, and there is nothing to break. It either works or it doesn't, but in these cases, there will be an error. When the car is fully warmed up, are the radiator pipes both hot? I had the wiring torn off the sensor, the problem was solved quite easily, but if all else fails, you can see the radiator options here https://boostyourengine.com/jeep-che...upgrade-guide/.I found the Best Jeep Cherokee Radiator Upgrade for my car, there are many options for different cars.