post #1 of Old 05-03-2013, 12:30 AM Thread Starter
CMARJEEP
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2002 WJ fan not turning on

Hey guys. My cousins WJ 4.0l has been intermittently overheating lately. Only at idle. We narrowed it down to the fan not turning on. It only has the e fan. I replaced the fan relay as that seems to be the most common problem but it didn't fix it. Then I tested the fan by hooking it straight to the battery and it kicked on full speed so it's not the fan. I also tested the connectors and everything is fine.

My question is whether the coolant temp sensor could be the problem. I assume that's what the computer reads to know to turn the fan on. I just can't think of anything else it should be.

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post #2 of Old 05-03-2013, 03:08 AM
cykaaro
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Does the fan come on when you put the A/C on?

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post #3 of Old 05-03-2013, 03:15 AM Thread Starter
CMARJEEP
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Quote:
Originally Posted by cykaaro View Post
Does the fan come on when you put the A/C on?
No. I've been reading that it should come on with the A/C though no matter what the engine temp is correct?
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post #4 of Old 05-03-2013, 04:24 AM
Mhancock2
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There is a relay that is known for blowing on these. All the manuals tell of a long process to get to the relay. YouTube it and they show a much easier way. I believe it is behind the oassenger's side headlight.
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post #5 of Old 05-03-2013, 09:26 AM
metalhead
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If the coolant temperature sensor is bad you would get a check engine light and most likely the engine would run rich. May be something in the wiring.
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post #6 of Old 05-03-2013, 11:03 AM
Highschool_WJ
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when is the last time you replaced the thermostat?
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post #7 of Old 05-03-2013, 11:31 AM Thread Starter
CMARJEEP
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Quote:
Originally Posted by Mhancock2 View Post
There is a relay that is known for blowing on these. All the manuals tell of a long process to get to the relay. YouTube it and they show a much easier way. I believe it is behind the oassenger's side headlight.
Did you even read my first post? I already replaced it. The problem is the fan. The relay is good. The fan is good. The wiring is good to the fan. I'm trying to figure out what triggers the fan to turn on.
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post #8 of Old 05-03-2013, 11:41 AM
metalhead
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The pcm triggers the fan to turn on using data from the coolant temperature sensor. There is also 2 fuses for the fan. A 40 amp fuse in the power distribution block and a 15 amp fuse in the junction block.

Last edited by metalhead; 05-03-2013 at 11:50 AM. Reason: more info
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post #9 of Old 05-03-2013, 11:54 AM
4Tom
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Engine control module turns on the fan.
Either because your temperature is high or AC is switch on.

Its not unheard of having a faulty new relay. They are very difficult to test because its a electronic controled relay and its output is pluse width modulation
The wider the pluse the faster the fan spins. Its a 12v pluse but a DC meter won't read it.

Ossiliscope could measure the output but very few of us have one so an ac meter might give you an indication of 6 to 8 ac volts.

The most common problem is the relay and repeated relay failure is worn fan.
Connecting the fan to battery doesnt tell you if the fan is worn or drawing too much current blowing relay. It only a crude check fan will spin with power.

I haven't tried it but believe if the tempture sensor is disconnected the fan should spin full speed. Although as yours isnt working with AC either I suspect you have faulty new relay or damaged wiring connection going to fan.

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post #10 of Old 05-03-2013, 10:10 PM Thread Starter
CMARJEEP
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Thanks metalhead and 4tom, that's the info I was looking for.
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