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Adding a Switch for the OE Electric Fan

L

lost honda pro

NAXJA Forum User
Location
Gainesville, FL
I understand this issue has been covered a few times, not nearly as much as the damned Taurus fan, but I still haven't found a viable solution. Yes, I searched.

For those of us with 97+ XJs, the auxiliary fan is controlled by the ECM. From what I understand, the ECM supplies a hot voltage to the ground side of the coil in the fan relay whenever it is off, and provides a ground path whenever it wants the fan on. The other side of the coil always has +12 V, so as soon as the ECM gives it a ground, the current flows, and the relay activates.

Obviously, you can't wire in a switch that grounds the wire, or you'll get a CEL. And I'd like to have the ability for the ECM to override my switch. Has anyone come up with such a circuit?

I know I could just but another relay and some 10 gauge, but I'd rather work with the system I have.

TIA for any insight,
Tim
 
I would, but if the ECM doesn't see the current from the relay coil when it switches to ground, it throws a CEL because it thinks the relay is bad. Unless...

Let me draw up a schematic, I think this may be simpler than I was imagining it.
 
Here's what I came up with, with your suggestion. I've never utilized diodes before, so I don't know if they're up to the task of blocking ~+14V DC, but in theory I think this should work:

AuxFanWiring.jpg


Assuming the resistor has a higher resistance than the ECM's path to ground, the ECM will think the circuit is working just as it should... This might actually work. Any thoughts?
 
I wired up a a switch on my 98 and it dosn't throw a code, i found a write up on here, but i cant keep the fan from coming on it just lets me turn the fan on if the jeep is off, i dont know if that is what your looking for, i do wish i could turn the fan off comletly for water crossing and such but it works pretty good.
 
im running the diode..12 volt diode..and ive had it on there for about 2 weeks now and it does well. and its still controlled regularly by the regular ecu. and i just spliced into my cig lighter for key power.
 
whitexj98 said:
I wired up a a switch on my 98 and it dosn't throw a code, i found a write up on here, but i cant keep the fan from coming on it just lets me turn the fan on if the jeep is off, i dont know if that is what your looking for, i do wish i could turn the fan off comletly for water crossing and such but it works pretty good.
Click to expand...

I want to be able to run the fan while the Jeep is running, like if I'm driving slow/idling, without engaging the A/C system, and without impairing the Jeep's normal function.

tommyboy said:
im running the diode..12 volt diode..and ive had it on there for about 2 weeks now and it does well. and its still controlled regularly by the regular ecu. and i just spliced into my cig lighter for key power.
Click to expand...

What are you powering? I'm under the impression that the relay just needs a ground path, not +12V. Are you powering the DB/PK wire? And do you have any CELs?
 
i have the diode spliced into the blue wire. then from there i have a power wire ran to my spdt toggle switch with a power wire spliced into my cig lighter hot wire so im protected by a fuse. the trick is all in the kind of switch. idk what CELs are. but id say scrap the relay idea...more wires then needed. imo.
 
CEL = check engine light

I'm not trying to add a relay, that'd be super simple. But also more $$ than I want to spend. I'm trying to manipulate what's there.

So you just add power to the Dark Blue/Pink wire, and the fan turns on? According to the Haynes/FSM/my VOM, that shouldn't do anything... Am I understanding you right?
 
You just ground the dark blue/pink wire via switch and that will activate the relay, which then sends power to the fan. I reset the cel(1491: aux fan) a few days ago and it hasn't come back. I still am gonna install a diode(cut the db/pin wire, solder diode to pcm end and then the other side of the diode will get the other side of the db/p and the wire from the grounded switch). If that doesn't work, the sure shot way is to have an a/b type switch that when the ground is switched to manually activate the fan, the db/p wire to the pcm is opened(what the diode should effectively be doing).
 
gradon said:
You just ground the dark blue/pink wire via switch and that will activate the relay, which then sends power to the fan. I reset the cel(1491: aux fan) a few days ago and it hasn't come back. I still am gonna install a diode(cut the db/pin wire, solder diode to pcm end and then the other side of the diode will get the other side of the db/p and the wire from the grounded switch). If that doesn't work, the sure shot way is to have an a/b type switch that when the ground is switched to manually activate the fan, the db/p wire to the pcm is opened(what the diode should effectively be doing).
Click to expand...

Thanks for the reply, I like knowing when someone has tried an idea and knows it works before I do it :D

tommyboy said:
nope no cels. i just wired up a diode and gave it power and no worries. and ya i just threw power to it through the blue wire and its fine.
Click to expand...

I don't know how your '98 is different than all the diagrams I've seen, but that DB/PK wire is always powered, so giving it +12v shouldn't be turning on anything.

Thanks for the responses guys!
 
lol its on roids! no but ok i took a 12 volt diode, spliced it into the blue wire, then took a three wire clamp thing a ma bob and hooked up 10 or 12 gauge wire to that, than ran that wire to a spdt toggle switch that was grounded to the body and also spliced into the cig lighter via the same clamp thing a ma bob and whalla!! and it still works the same as stock. i thought it was harder using the stupid relay honestly. idk where the flock you guys are getting codes. wierd.
 
Bringing this thread back from the dead. Ok here s my problem...my fan switch set up finally took a shit....I had it hooked up to my 12 volt plug in and I've blown 2 25 amp fuses. The way I had it set up was with a diode spliced into the blue wire running to my fan and idk if it was working because I noticed that when I ran my a/c it stopped letting my fan go on and also I noticed my fan wouldn't kick on at high temps. And the other day I did some tinkering with wires and hooked the power supply to my switch straight to my battery and got no response. So now I'm wondering 2 things, did I eff up something electrically pretty bad, did I cease my fan in a way, and what is another set up besides the diode idea I can utilize?
 
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