Ok so my cooling fan is not working on my 4th gen prelude...i already replaced the relay,thermostat, cooling fan switch and bled the system and nothing...i think their might be a short somewhere or i might be missing something else so i was wondering if anyone can help me out or if anyone has the cooling fan wiring diagram...thanks in advance...

 

Try jumping the green cooling fan switch with a wire and see if it turns on while the car is on, if it does then it's probably your module.

 

Did you check your fuse?

 

I second the fuse check.... The fan will easily blow a fuse if something (grass, wheat, corn stalks from sliding sideways into a ditch.... yeah, done that :D ) blocks the fan from turning.

If the fan doesn't start on the temp sensor test above, you can test the fan itself - pull the smallish square black relay that is almost in the center of the under hood fuse box. (There are two larger relays just in front of it.) Jumper the fuse box across the two terminals furthest to the right as viewed when sitting in the car. (toward passenger side).

The fan should immediately come on - I don't think that you need the key on either, but if it doesn't come on, try turning the key all the way on. On most cars, the cooling fan can run even when the engine is off and will do so in hotter climates when you first turn the car off.

If the fan runs, then this time, but didn't when you jumpered the green temp sensor, then the relay is bad.

 

X2 for checking the fan itself, it may have died.

 

how do i do that

 

yes and they are still good

 

To check the fan switch put your ignition key in the run position, lights on the dash will come on. Don't start the car. Go to the engine compartment and remove the connector on the thermostat housing. Take a short piece of wire and jump the connector. You should hear the fan switch relay click followed by the fan turning on.

 

there is also a fan timer box next to the ecu. little black box. could have gone out. mine is on a switch now but it used to come on with the timer. even when the car was off and i was inside the timer would be cooling it down. fan blowing like crazy. not anymore, but you can find these little black boxes on ebay for cheap.

 

Be sure to check that it has a nice clean ground as well. The easiest thing to do would probably be spend the ~$50 on a half way decent multi-meter so you can do some tests (open circuit, voltage drop, etc.) This would save you a lot of time guessing and money throwing part darts at it, and anytime you or one of your buddies had another electrical issue you'll have it, it'll pay for itself in no time trust me.

 

2.99 right now at harbor freight!!!

 

Here you go 4th Gen drawings.

In the electrical attachment, wiring is pretty straight forward and the fan relay is on the second page. This is the entire electrical system diagram for the car.

The Cooling attachment is how to test and trouble shoot the cooling fans in all their glory.

 

could anyone tell me how to run the fan direct without a toggle switch

 

You could grab a relay from your handy parts dealer and wire one side of the coil to the accessory or the fuel pump fuse and the other side to ground. Any time the car is on, the relay will close.

Then hook up a wire from the battery to one of the relay contacts and from the other relay contact to the fan. Just watch, the fan has two wires. Because it is plastic, there is no frame ground. Wire from the relay contact goes on one side and a wire to ground on the other side. Anyway, just make sure the fan is blowing air toward the engine when it comes on.

I would also put a fuse in line where you hook to the battery. If you want to get fancier, there are some fan controllers with a thermostat on the relay.

 

To complicated...any easier way

 

The fan pulls quite a bit of power, but you could hook it up to the low beam headlight power. You will want to test it a bit. I think that the fuse will handle the additional power, but it may not.

 

Any other ideas out there

 

The problem is that the fan itself does not have a switch, so if you hook it up directly, it will run until the battery is dead. It either needs a relay controlled by a switch or thermostat, or you must run it off of something else that has a big enough relay.

The fan will put a considerable load on the alternator and battery when it is running. When you are going more than about 30 mph, you will not need the fan (unless your are driving hard) and switching it off will add measurably to your gas mileage.

 

hi i have a similar problem and i'm not sure why fan still doesnt want to come up... :/

this was F20A4 prelude 94, I swapped my h22a jdm obd1 engine which was working in my last prelude perfectly, and since i did the swap still the same thing - fan not working.

Relay is fine, fuses all fine, no air bubbles in coolant at all, new thermostat ( tried with and without it ), new radiator, fan checked - working properly.

and still - when i jump the plug ( ECT sensor A on the thermostat) the fan is working... when its plugged to the sensor - no signs of coming up.

I have external ECT gauge, and strange thing is, that it comes to 96-97 degree and suddenly something around 105-110 appears... fan still not working, but i'm wondering what does that sudden raise of temp mean ? any ideas ?

 

Hey make sure you check your plug because I was having the same problem and I was thinking it was the senor but come to find out it was a plug . the little was not connecting to the sensor

 

My fan won't come on either, I used a cotter pin where the relay is and it came on, a new relay did not fix it, I tried jumping the wires on both sensors, nothing, I checked the sensor wires with a test light and neither had power, also the interior fan won't come on at any speed, what should I check for next

 

after searching for bad relays, loose ground wires, and everything else that could possibly keep the fans from coming on, I decided to check the fuses once again for any blown ones, only to notice that the one fuse that powered the relays, cooling sensors and fans was missing.... I replaced it and everything works now.

 

try checking the #9 fuse

 

If he hasn't fixed it yet after 4 years there's no hope now. Who knows if he even still owns the car hes working on in this thread lol... Check the dates before replying.

 

Helped me out lol, thanks bud