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How can I add an auxilary fan bypass switch?

bhicks

bhicks

NAXJA Forum User
Location
Forest Falls, CA
I have a 2000 XJ and I would like to run a switch to my dash that will allow me to flip on the auxilary fan whenever I want. My work is at 1,500 feet and I live at 6,500 feet so I am going up and down a mountain every day. I really do not want to stress or overheat the engine, especially with a weak 0331 head. As of right now it runs between 215-220 everytime I come up the mountain. AS of right now the auxilary fan doesn't kick on until I hit 220. I would like to manually control it so I can kick it on when it gets around 200-210. I have already relpaced the radiator with a 3 core CSF and replaced the waterpump, thermostat, all hoses, temp sensor, and flushed the heater core. The only thing left to improve cooling is the overide switch. Please advise.
 
lost honda pro said:
I came up with a switch circuit that allows the use of the fan at any time (even with A/C) without a CEL. Let me find the diagram...
Click to expand...

Sounds great. Send it my way when you get a chance. If you could let me know where you got your parts I would greatly appreciate it. Also, what is a "CEL"?
 
CEL=Check engine light.
I don't know about the newer models, but on my 89, I ran a fused wire to a switch on the dash, and ran a wire from the switch to the signal wire on the fan relay.
 
Motornoggin said:
CEL=Check engine light.
I don't know about the newer models, but on my 89, I ran a fused wire to a switch on the dash, and ran a wire from the switch to the signal wire on the fan relay.
Click to expand...

I was just informed that the 2000 auxiliary fan may be different. I was told that auxiliary fan always has 12v of power going to it. The ECU simply flips on the ground. If that is the case, then all these wiring schematics people have sent me will not work. All I would need to do is run a switch with a ground to the ground wire coming off the fan. No relay or fuses would be needed. Any 2000 owners out there that have added the switch? I would really like to know if this fact is correct and if so, how the switch was added.
 
bhicks said:
Sounds great. Send it my way when you get a chance.
Click to expand...

The link to the thread is in my first post.

bhicks said:
I was just informed that the 2000 auxiliary fan may be different. I was told that auxiliary fan always has 12v of power going to it. The ECU simply flips on the ground. If that is the case, then all these wiring schematics people have sent me will not work. All I would need to do is run a switch with a ground to the ground wire coming off the fan. No relay or fuses would be needed. Any 2000 owners out there that have added the switch? I would really like to know if this fact is correct and if so, how the switch was added.
Click to expand...

All the 97-01's are the same, as far as I know.

If you'd have looked at the circuit diagram I referenced, you'd see that the DPDT switch grounds the fan relay signal wire and sends power to the ECM. This fools the ECM and activates the fan.
 
bhicks said:
I was just informed that the 2000 auxiliary fan may be different. I was told that auxiliary fan always has 12v of power going to it. The ECU simply flips on the ground. If that is the case, then all these wiring schematics people have sent me will not work. All I would need to do is run a switch with a ground to the ground wire coming off the fan. No relay or fuses would be needed. Any 2000 owners out there that have added the switch? I would really like to know if this fact is correct and if so, how the switch was added.
Click to expand...

It will not work. The ECU can tell when the fan relay in on, if it is on when not commanded, it will turn on you check eng light. You need to install a 30 amp relay, tie into the large blue fan wire in the harness on the fire wall.
 
lost honda pro said:
The link to the thread is in my first post.



All the 97-01's are the same, as far as I know.

If you'd have looked at the circuit diagram I referenced, you'd see that the DPDT switch grounds the fan relay signal wire and sends power to the ECM. This fools the ECM and activates the fan.
Click to expand...

Hallo. lost hond pro. Can you please send also me the circuit diagram. I can't find it back in the normal diagram.
thanks.

'92 XJ
 
Last edited:
lost honda pro said:
The link to the thread is in my first post.



All the 97-01's are the same, as far as I know.

If you'd have looked at the circuit diagram I referenced, you'd see that the DPDT switch grounds the fan relay signal wire and sends power to the ECM. This fools the ECM and activates the fan.
Click to expand...

I did look at your thread, but for some reason the server here at my work blocked all your pics. All I could see was the text and since the text only referenced the pics I couldn't really get anything out of it. I will be looking over your thread much closer when I get home from work and am able to see the pics in the thread. If you have a written up diagram of the schematics of how to wire up this switch, I would greatly appreicate you sending it my way. You could pm me with it or email it to me at [email protected]
 
Last edited:
i used the stock relay for the fan on my 95 jeep

the PCM no longer have control of the fan as i chopped the wire off it and use that wire to rig up the switch on dash to control it. also i rigged up that the fan CANNOT be running constantly even the ignition switch's off. even before i do that, i used the one on the relay for the ground and it worked before i started wiring and ended up it dont work and i had to ground another signal wire as i believe the PCM control that one and i elimated that.

il have my fan on ALL time as its running, but will only be turned off when the weather's cold or i will be water fording as water will break the elec fan easily
 
oh one more thing, i tinkered with all of this, my CEL never came on, so i couldnt tell if it was requested or not as its old jeep and the CEL light probably inoperative anyway lol
 
FordGuy said:
It will not work. The ECU can tell when the fan relay in on, if it is on when not commanded, it will turn on you check eng light.
You need to install a 30 amp relay, tie into the large blue fan wire in the harness on the fire wall.
Click to expand...

I've been running my fan this way for 6 years with no problems.
Oh yea, mine's a 2000...
 
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Okay, everything is now hooked up and the fan is coming on with the switch. I have no check engine light, so I am very happy. I have just one last extremely retarted question. Which way is the air supposed to blow? As of right now the fan is sucking air through the radiator and blowing it towards the engine. I thought this was correct, but my neighbor just came over and said that it backwards. He said that I hooked into the wrong wire witched reversed the direction. I hooked into the grey wire and not the black wire. Some of you guys said look for the green wire and others said look for the blue wire. I feel like I am trying to turn off a bomb. It really doesn't help that I am color blind. Either way one of us is completely retarted and I need you guys to tell me which.
 
FordGuy said:
It will not work. The ECU can tell when the fan relay in on, if it is on when not commanded, it will turn on you check eng light. You need to install a 30 amp relay, tie into the large blue fan wire in the harness on the fire wall.
Click to expand...

While you are correct that the ECU knows when the fan relay is activated, you are wrong that a CEL is imminent. The diagram I referenced shows a way to power the relay and fool the ECU simultaneously, with a single switch.

wim hoppenbrouwers said:
Hallo. lost hond pro. Can you please send also me the circuit diagram. I can't find it back in the normal diagram.
thanks.

'92 XJ
Click to expand...

Please see the link in my first post on this thread. Post #5 in that link has the diagram.

95' heep said:
oh one more thing, i tinkered with all of this, my CEL never came on, so i couldnt tell if it was requested or not as its old jeep and the CEL light probably inoperative anyway lol
Click to expand...

As far as I know, the pre-97 XJ's ECUs didn't control the auxiliary fan, so the CEL wouldn't be an issue for you.

bhicks said:
Okay, everything is now hooked up and the fan is coming on with the switch. I have no check engine light, so I am very happy. I have just one last extremely retarted question. Which way is the air supposed to blow? As of right now the fan is sucking air through the radiator and blowing it towards the engine. I thought this was correct, but my neighbor just came over and said that it backwards. He said that I hooked into the wrong wire witched reversed the direction. I hooked into the grey wire and not the black wire. Some of you guys said look for the green wire and others said look for the blue wire. I feel like I am trying to turn off a bomb. It really doesn't help that I am color blind. Either way one of us is completely retarted and I need you guys to tell me which.
Click to expand...

The fan is supposed to pull air through the radiator, toward the engine. You are correct. Think of it this way, if you were idling in traffic, at 10 mph or so, would someone really design the fan to push air against your direction of travel? That makes no sense.

Glad you figured it out, and I'll assume your set. If you need anything else, let me know, I can provide the stuff you PM'd me about if you'd like.
 
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lost honda pro said:
While you are correct that the ECU knows when the fan relay is activated, you are wrong that a CEL is imminent. The diagram I referenced shows a way to power the relay and fool the ECU simultaneously, with a single switch.



Please see the link in my first post on this thread. Post #5 in that link has the diagram.



As far as I know, the pre-97 XJ's ECUs didn't control the auxiliary fan, so the CEL wouldn't be an issue for you.



The fan is supposed to pull air through the radiator, toward the engine. You are correct. Think of it this way, if you were idling in traffic, at 10 mph or so, would someone really design the fan to push air against your direction of travel? That makes no sense.

Glad you figured it out, and I'll assume your set. If you need anything else, let me know, I can provide the stuff you PM'd me about if you'd like.
Click to expand...

Thanks for being so helpful. If I have any more questions I will let you know, but I think I am set.
 
Alright, so I took it out for a test drive last night and drove it in to work this morning. The fan now comes on at the switch and no check engine light comes on. Once I got it up to normal temp I flipped on the switch to see what would happen. Both times the temp dropped about 15 degrees in about 60 seconds. I am VERY pleased with the results. I also used a flat mount switch that I mounted just in front of the ebrake handle on the middle consolt. It looks like it belongs there. I will post up a pic of it when I get off work later today. Thanks again guys for helping me out.
 
A little late since you have already completed this, but I used this diagram on my 01 and it has worked great for 2 years.

482928_45_full.jpg


From this thread: http://www.naxja.org/forum/showthread.php?t=60972&highlight=aux+fan+override

Another benefit of this mod is you can leave the fan running when you stop on the trail to avoid the hot start rough idle the 00-01s seem to be plagued with. Definitely one of my favorite easy mods to do.
 
wim hoppenbrouwers said:
Hallo. Maybe a little simpeler:
But this is a very safe switching, because there is only one thin ground wire into the cabin.
Click to expand...

I agree, once I realized that Jeep made the ECU switch the ground instead of power, I started wiring things that way and I like it a lot more than running a fused power line into- and out of the cabin. I don't know that it's a whole lot safer as both scenarios use a current carrying wire in the cabin, but it's definitely easier as far as I'm concerned.
 
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