The Mick

I have a '96 Cherokee Country and the aux fan will not come on via the coolant temp sensor. It works with the A/C ext and when I pull the connector from the coolant temp sensor. So I replaced it and still nothing. I'm getting an ohm reading of 633 +/- at 220* +/- on the old one and similar the new one.

At what ohms should the fan kick on and what temp should that be at?

djb383

On at 218F coolant temp, off at 209F.....on when a/c compressor is on.

EZEARL

The aux fan on my '96 hasn't come on due to the coolant temp since I replaced a bad fan clutch. Otherwise it's working as it should. So unless you feel your having an overheating issue it sounds like yours is working as it should to.

The Mick

Thats about what I thought. Not working tho'

Yup overheating I have to run the heater to cool it down. I thought it was a bad sensor so I replaced it and no go. thought maybe the one from O'Reilly's was bad so took it back and got one at Napa again no go.

EZEARL

Have you tried pulling any codes?

The Mick

I'm a bit stumped at this point as I mentioned when I pull the connector from the sensor the fan comes on so it seems the rest of the circuit is fine. Though I must say electrical is not one of my best subjects so there could be any number of things I'm missing.
For clarification the thermostat is working as is the rest of the cooling system. But sitting in traffic or red lights it heats up and the fan does not kick on.

The Mick

Not yet I don't have a code reader. Is there a key trick or something to get it to blink the codes for this model?

Edit: found the trick online, will go check it and get back.

EZEARL

This should help:
http://www.xjtalk.com/showthread.php?t=11574

Also need to fix the overheating issue also then. Fan clutch working?

The Mick

No codes.
I'll go warm the jeep back up and check the fan clutch.

EZEARL

You should have gotten 12 and 55?

Also had this saved:
"If the fan comes on with the a/c you know that the relay, it's power feeds, the fan, and all associated wiring are functional. If your coolant temperature is going over the 218 degree mark, the coolant sensor is giving the powertrain control module (PCM) an accurate reading and the fan isn't coming on then the problem has to be internal to the PCM."

So you may want to verify your coolant temp.

The Mick

Sorry the Wife got me side tracked for a moment.
Yes 12 and 55 but nothing else. Two questions, I did just pull the negative battery cable to get rid of the check engine light from having the connector off of the sensor. Would it take longer than a warm up ride up the street to show anything else? And If it is the PCM would it not give a 53 or is that for more of a catastrophic fail of the PCM?

Edit: And yes the fan clutch is fine as far as I can tell plenty of resistance. As far as coolant temp I have a fairly new thermostat and a brand new temp switch. Watching the gauge it appears close as it reaches the 210 mark it falls back as the thermo opens. But I've no way to properly check right now.

Thanks for your help.

The Mick

I read this thread and post #9 shows a good test for 97-01 XJ I'll find an equivalent resistor and try this soon.

https://www.cherokeeforum.com/f2/ele...coming-161807/

The Mick

Update.
Today I ran the test from the above thread.

My results were that with a 470 ohm resistor the fan came on just fine. Went ahead and added a 150 ohm to it making it a 620 ohm and fan would not run. So the circuit seems fine.
I then took the sensor out and placed it in an electric kettle and clipped on to my multi meter and boiled it until it stopped lowering in resistance. The result was 747 ohms never got lower so at 212* that was it's lowest reading. I then did the same with my old sensor and it went to 719 and no lower. As of last summer the old one worked fine but I had other cooling issues that have since been resolved.
Ant just to clarify I also bought and returned a sensor yesterday from O'Rilleys as it didn't function but I did not boil it to test. So are these all junk or am I really missing something here?