Hi
i have 98 4.0 sport.
the electric fan does not come on even the temp passes the half way. It was working until last week.

1. changed the relay no change
2. changed the temp sensor no change
3. connected the fan to the battery directly . It works
4. removed the connecter from the temp sensor . Fan Works and check light turns on
5. Turned on the ac and fan works

so what is my problem?
Thanks

 

I would check the temp sender for the gauge and maybe the temp gauge also . the gauge is known not to be vary accurate .

 

It should come at 218*F. Do you have an ODBII reader to verify the coolant temp actually hit 218? An infrared gun aimed at the t-stat housing will also get you close.

 

'98's only got one sender & as it's recent failure it seems unlikely the temp. suddenly isn't reaching 218*

The only thing left seems to be the wire from ECU to relay, although I must confess the fan circuitry's too complex for my simple mind.

 

Sadly an obd2 reader is no proof of accuracy. It will read whatever the sender thinks the temp is , but as that temp signal is also sent to the gauge, unless the gauge is physically inaccurate they will usually show the same temp regardless of what the true temp is. Only way to verify is with a quality temp gun or to remove the sender and place in a pot of boiling water while reading the resistance. Should be approx 675 +/- 50. That 218 is a longer bit past the 210 mark then one would think

 

I think the 218* is a bit of a red herring because the issue is, that the fan doesn't cut in now when it did a week ago.

I can't see how the sensor could've suddenly failed so that it no longer triggers the fan but doesn't alter the temp. gauge reading - but then, I've been wrong before.

 

So the problems looks to be wiring of the relay
for 98 xj
does anyone know
where does 85 - 87 -30 ... pins of the fan relay goes ? Whichone goes to the pcm ? Battery ? Sender ?

 

Beyond 30 normally being being the power supply & I'd expect 87 to be the fan I'm really not sure because not only does the fan only work when the ignition's on, it has 2 triggers, the the sender & the a/c.

 

Anyone that works on these cars needs to free download the FSM, with all circuit diagrams, and diagnostic procedures

You can get them off this site and others

 

If that were true, this forum wouldn't need to exist, nor would any other that's primarily tech queries.

 

Several 1998 manuals here:
https://archive.org/search?query=199...herokee+manual

 

sorry, but why would anyone not download the free FSM ?

I presume that you have

Trying to help the gent out here

 

You know what they say? If something sounds too good to be true, it probably is.

Not for the XJ's I haven't, never had the need; I've had others & been less than impressed: the KJ one is truly dreadful; right down there with the ever wonderful Haynes "Book of Lies" (as it's known in other circles).

I understand, & appreciate, your motive but think suggesting you can't manage without an FSM is overstating it a bit. After all, we all managed perfectly well before they were readily available.

As for OP's question, the answer might be in the other, recent, similarly captioned thread.

 

The XJ one is excellent, over 1700 pages. I would also advise an owner to download the Factory Parts Manual, and the Technical Diagnosis Manual (if you can still find it online )

As a former technician, soon as one needs to do electrical fault diagnosis, I am not sure how else one would go about it apart from Youtube (or as you say a forum )

Of course I often work on equipment without referral to any manual, but it cannot hurt to have it and the answer to the PO problems resides within its pages

This reminds me of a very bad joke;

What is the similarity between a 9V battery and a ----- ----- ******** ?

If you have heard it you will know the answer, told it to a very prominent Sportsman in a bit of a joke telling competition on a father/son football weekend, he broke down completely with laughter

 

First, to the OP. Have you checked the actual temp at the thermostat housing as suggested earlier? If it doesn't reach the right temp, the fan won't kick on unless you turn on the AC. So far, the fan IS working correctly.

Jeep uses different pin numbers for the relays in the diagrams, that's why you need an FSM (amongst many other reasons). For now, here ya go:


The PDC, Note the pins on the Cooling Fan relay socket.



The schematic for the relay.
Pin C10 provides the battery Positive (this corresponds to pin 30 on the relay)
Pin C14 is the N/O pin to power the fan (Pin 87)
Pin C11 is the + side on the coil (Pin 86)
Pin C13 is the ground side of the coil (Pin 85). The relay is grounded by the PCM.
(Note: Pin C12/87a is not used)




So when you turn on your AC, the PCM gets an AC Select signal. Assuming the AC system is OK, the PCM grounds out the AC Clutch relay and the Fan relay. The relays energize and power on their respective devices. The PCM also gets temp data from the coolant temp sensor. When the PCM detects coolant temps of approx 218F, it grounds the fan relay and turns on the fan. So if the temp doesn't get to 218-ish, the fan won't come on unless you turn on the AC.