'01 4.0 electric fan wont run

This is a friends jeep so I dont know what has been tried but the skinny is the electric fan wont come on. What tells it to come on? IIRC it has to do with the AC but I dont know much about any thing that new. I need to be able to tell him what to do over the phone and as I dont know anything about the new ones I also dont know where anything is in the engine bay. He needs to have it fixed by this weekend so quick help would be great.

It's basically the same setup as on all XJ's and MJ's. When the A/C compressor cycles on the fan should start, and they go off about the same time. The fan will also come on at 230 degrees to help cool the engine in extreme overheat situations.

I'm not sure if it was factory on the '01s but '97-'99s had a TSB for the headlights dimming when the fan came on. The fix was to install a seperate relay box between the factory harness and the fan. It's located on the frame rail in front of the air filter box.

I had the same question with my '00 cherokee.

I posted a question in this forum and did a search...basically I got different answers.

From what I read, electric cooling fan on OBDII cherokees...98-01 is controlled by the ECM. The ECM will turn on/off the fan based on AC system requests and temperature readings.

Most posts and articles I've read stated that the fan should come on when the AC is turned on. I think this is true on vehicles that just have electric cooling fan or fans. Since the 98-01 (and mybe others) cherokees have a mechanical fan for primary cooling, I'm not sure this is true. The electric fan may or may not come on when the AC is turned on.

I have yet to see my turn on...but its been relatively cool lately where I live. On my cherokee, I've verified that the fan and fan relay is good. The ECM is just not sending a signal (ground the relay) to turn it on. Now my ECM might be bad...but since it is not running hot (I think), I'll wait for warming weather to do further testing.

from http://findarticles.com/p/articles/mi_m3102/is_10_123/ai_n6358902

"The system is simple and direct, with the PCM controlling the A/C clutch and the secondary engine cooling fan through a pair of relays. The 4.0L package has a belt driven fan as well as an electric cooling fan to assist in case the A/C head pressure goes too high or the engine gets too hot....

The secondary fan only runs when the PCM determines it is needed, either in response to engine temperature or a ground from the A/C high pressure switch. As Ed's Jeep heated up and the A/C head pressure climbed, we watched the high-pressure switch open Circuit C90, giving us 12 volts once again, and within a second or so, the PCM triggered the cooling fan relay to energize the secondary fan."

The fan motor might be toast. Try another one if you can get ahold of one cheaply. I guess you could run it straight off the battery too and see if it kicks on.

My 98XJs electric fan would only kick on for a few minutes and then wouldn't pull very hard after a few minutes of running. After that it wouldn't kick on at all. I quess the motor was toast. This was at about 90,000 miles. I replaced it with a new fan assembly and all is well. Good luck.

db209_2000 said:

It's basically the same setup as on all XJ's and MJ's. When the A/C compressor cycles on the fan should start, and they go off about the same time. The fan will also come on at 230 degrees to help cool the engine in extreme overheat situations.

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The fan should come on at ~220*F, not 230, but otherwise you're correct. If the fan doesn't come on even when you switch on the A/C, the fan relay could be at fault. If it does come on when you use the A/C but it doesn't come on when the engine's starting to overheat, it's lileky that the coolant temp. sensor in the t'stat housing is at fault.
Hotwire the fan to the battery and see if the motor works at all.