I have been having issues with the auxiliary cooling fan on my 01 Jeep XJ.

Having done some fairly extensive troubleshooting (the fan motor is good, relay is good, engine temp sending unit is good, AC is charged), but the fan won't turn on regardless of whether the AC is on or the vehicle is running at high temperature. Doing my research, I stumbled across a post on how to troubleshoot the Aux fan on a Jeep XJ. Some of you are probably familiar with it -- I found it referenced on this forum earlier.

http://www.lunghd.com/Tech_Articles/..._Diagnosis.htm

This is evidently a webpage made from a previous document on troubleshooting the aux fan on an 1988 Jeep, which one can see here:

http://jeepgarage.free.fr/OWN/engine...ling%20fan.pdf

Having worked through the troubleshooting, I've noticed the following things (refer to the figure below when I reference relay connectors):

1. There is no mythical "Fan Diode Assembly" on my 01 Jeep, so I can't replace it, regardless of what the webpage says.
2. Connectors 4 and 5 are always hot -- they have 12V all the time, regardless of whether the vehicle is on or off, regardless of whether the AC is on or off.
3. Connector 1 is always off -- it has roughly 0V all the time, regardless of whether the vehicle is on or off, regardless of whether the AC is on or off.
4. Connector 2 is the mystery. When the vehicle is off, it has 12V. When the vehicle is on, it has approximately 0.2 V. This is regardless of whether the AC is on or off.

This really bothers me. Should #4 and #5 always be 12V? And what is the deal with #2?

Any thoughts from the Jeep sages?

 

Jump 1 tp 4, no keys, fan should run.
Diode assembly is just referring to the fan motor itself.

Check the following-
Battery
15 amp fuse at #10 on kick panel
fan relay (swap in another one if needed)
clutch relay (rectangular black forward of the fan relay-swap as above)
low switch - (unscrew and then re-tighten should get a little spurt of PAG oil)
high switch -same as above
temp switch on water outlet - if all else is good, jumping this connector should run the fan)
the fan itself - power and ground to fan to see if it works

My fan was bad, caused the system to not work.
Then I popped the fuse while testing circuits, did not find it for a week.

Now ice cold

 

I had something like this on my starter relay. There was some deteriorated connection and I just bridged the 1-4 slot with a piece of wire and then Ive never had a problem again

I imagine you could just bridge it also, unless it causes it to stay on all the time

 

well i want the fan to stay on all the time! how would this happen! no one seems to want to tell me haha

 

Well it only kicks on when it's needed, that would be loud as hell if it was all the time,

Get a 4" piece of wire, strip and twist each end. Then bridge 1 and 4 and see if it works for a temporary fix

 

Only problem with jumping 1 to 4 is that 4 is always hot. Always. As in, jeep is off, but fan will still be running.

As for the above-mentioned list...
Battery is good.
15 amp fuse is good.
Fan relay should be good -- replaced it with a new one, but don't know how to test it.
Temp sending unit should be good -- replaced it with a new one.
Fan itself runs whenever I jump it to the other terminals, or whenever I otherwise apply 12V.

I haven't checked the clutch relay. Will do though.
Also, haven't checked the low / high pressure switches. If you could talk me through that a bit more thoroughly than the above (e.g. - is the vehicle running? is the AC running? etc), that would be outstanding.

 

In your 01 pins 4 and 5 are fed constant hot from seperate fuses. Pin 1 goes to the fan. And pin 2 goes to the PCM. The computer grounds pin 2 when it approves the A/C request (PCM monitors pressure switches in A/C lines). The PCM has the ability to kick the fan on when the engine temp gets too high or when the A/C is switched on. If the wire between terminal 2 and the PCM is good id say you have a bad computer.

 

Gonna have to expose my ignorance here... I thought the PCM was one of the computers in my jeep (with the other being the ECM). Someone kindly set me straight on this.

Next question - is there any way I can test my PCM before I shell out to replace it? I would think other issues should be taking place (e.g. - stalling out) before the aux fan just won't turn on. What other indicators should I be looking for to confirm its the PCM?

Any suggestions greatly appreciated.

 

If your fan is not turning on automatically, I wouldn't get too excited about replacing the computer. If you want control of the fan, wire in a switch and turn it on whenever you feel the need.

I've read threads of this and that not working qite right and the fix was to rewire some connections between the airbox and the ECM. I don't know that to be your issue, but just mentioning it in passing.

 

In some cases the computer can be bad but still run properly. Id check all the PCM grounds and the wire from the PCM to the fan relay. If all checks out good id say the PCM is at fault. Personally id re-wire the relay to trigger it without the PCM.