I've been noticing some temp creep while sitting in traffic. I have a scangauge and I can see what the PCM sees from the temp sending unit. The temp will climb up to 218-220 and the efan doesn't kick on. It often will take till the temp is 223-225 before the fan will engage. Then it will only stay on till the temp is around 215*. The FSM says it should come on at 217* and go off at 209*.

The efan is the original, the build date states it was made in 1997. I replaced the efan relay and that didn't help. I'm thinking of replacing it, but I'm hesitant to think that is sole problem. Is there anything else to check before concluding my PCM is being lazy? Or could the efan itself be the real problem?

well, verify if the fan is getting voltage prior to its coming on if yes than its bad if no its good.make sure the contacts the relay plug into arent loose it took me a long time to figure out that was my problem after replacing my fan twice. flip the pdc box over and check the spade connections from the bottom to make sure they are seated all the way on the relay

One other thing: the efan will come on if I turn on the a/c.

Thanks, I'll look into this. I had a short in my PDC once before...

well the a/c triggering the fan kinda takes the relay issues out of the equation also pretty much says the fan is ok probably time to look into a secondary way to trigger the fan by temperature

The 97-99 settings are 218*F on, 209*F off. The 00-01 settings are 223*F on, 217*F off.

Looks like your XJ is behaving like a 00 or 01. I don't know for sure why Chrysler upped the fan on temp on the 00 & 01 but I've heard it may have something to do with trying to meet higher emission standards (?). Apparently the higher temp won't hurt the engine.

The Engine Coolant Temperature sensor is the same part number for 97 thru 01 (56027873). Using your scangauge you can indeed see what the PCM sees from the temp sending unit. You should also be able to see the Intake Air Temperature as well. After the Jeep sits over night and the coolant and engine core are stabilized, and before starting the engine, compare the ECT and IAT temps - they should be within a degree of each other. If not, you may want to install a new OEM ECT and see what it does.

I don't think your radiator electric fan poses a problem in this situation.

Thanks for the info. That is very interesting about the temp settings. Is there any way to tell if I have an 00-01 PCM installed on my 98?

The PCM part number is on a decal on the radiator side of the PCM.

All these PCM part numbers are for the 4.0 liter, auto transmission:

1998 - 56041 537AB - California Emissions

1998 - 56041 534AB - Federal Emissions

2000 - 56041 635AE - California Emissions

2001 - 56041 801AA - California/50 States Emissions

What does ECT and IAT stand for?

Great thread... should be stickied perhaps.

And its another good reason to own a Scangauge.

Engine Coolant Temp

Intake Air Temp

Here is mine

2000 - 56041 634AF

Federal emissions.

What's your build date (on driver's door decal)?

03 2000