Hey guys - hope the forum can shed some light on the engineering design function of the electric fan. My request is a description of the control parameters & thresholds causing the e-fan to turn on in a 1998 XJ, a robust test cycle to determine a "all clear" for the engine coolant temp, or a better electrical test. Other posts helped, but did not answer all the questions - hope you can help. Here is the detail and what I have done so far...

Typically, my '98 temp gauge stays right at 210F. A few weeks ago (90+F ambient), I got caught idling in traffic for ~15 min. The temp gauge rose to the red zone and the red "Check Gauges" light came on. Traffic cleared soon after and 1-2 minutes of driving had the temp back down around 210. AC blew cold the whole time (turned it off when "in the red"), and turned back on when it dropped. At least that made me feel good about the cooling system. This is the only time the coolant temp needle or red 'Check Gauges' light have been active - but I have not pushed the engine past any situations described below.

Diagnostics:
1. Confirmed mechanical fan clutch good = noticeable airflow jump as temp increases.
. a. Based on reading other posts (and replies) - did not accept as this 'subjective' test as good enough.
. b. Performed the newspaper test (rolled an entire newspaper up as tight as possible & jammed it into the fan <1 min after starting the engine. Newspaper chewed to shreds faster than I could shove it in).
. c. I concurred w/ other posts that newspaper test not robust.
. d. Replaced mechanical fan clutch w/ new unit from Autozone.
. e. No change to following behaviors described below.
2. Confirmed electric fan bad = sent 12V directly to fan connector. Removed and blades difficult to spin (ok - bad motor).
3. Installed new e-fan - confirmed function and polarity (concern based on other threads) before install.
4. New fan did not turn on in vehicle. Testing = idle in driveway until coolant reaches 230 and turn AC off/on.
5. Confirmed temp sensor good = IR gun & temp gauge <5F apart
. a. Initial check good to ~220 F
. b. Later checks showed ~240 on cluster gauge (not in red) & 260 @ coolant sensor w/ IR gun
6. Checked fuses = all good
7. Checked relays - swapped starter & e-fan relays = vehicle still starts
8. Confirmed good ground from e-fan harness connector to neg. battery terminal.
9. Checked voltage @ wire harness connector = 0V under all conditions. (Might not matter, but the very first voltage check before pulling fuses/swapping relays the voltage read 0.8V with AC on, but all later checks read 0V).

Through all of this I have developed a fairly repeatable drive cycle. It seems that the only way to get the temp to rise >230 F is with ambient 90+, driven (something to build heat in the engine), idle 5-10 min, A/C on. Take one of those items away and it stabilizes in the ~230 range. Based on all this testing - I am confident another "Red Zone" over-heating event would happen because the electric fan still does not turn on even though I chicken out when the gauge reaches ~240 F and the IR gun says 260 F.

Any suggestions thoughts - did I miss/mess-up something? I am willing to try anything with a small piece a sound logic. But I would like to have more confidence before getting caught in a bad spot again. Thanks.

 

You have been doing good checking all these things, and maxed out my knowledge of the E fan system. Fan should cycle if AC is on, so you might want to check that circuitry as well. Other than that, temp sensor should trigger the relay on at I think 212 F.

Double check your fuses. A stalled fan motor can pull a high load and blow a fuse. Also, are there any fusible links on the 98s? I don't think so, but you should check.

Start tracing wires, looking for breaks or nicks in the insulation and wire. Seeing 0.8V before doing work and then seeing 0V makes me think you either installed faulty parts or disturbed something. 0.8V is still not good, indicating you might have a fault or issue with the wiring. Check your current at the source side of the system when it triggers on. If you have a high amperage, you've got a fault somewhere.

Check your ground connections, generally a good thing to do when faced with XJ electrical ghosts.

 

did you check voltage at harness side of connector just before and after you reach switch temp? Verify it is getting the 12v signal or is it a ground controlled circuit?

 

look through the good info thread, sticky at top of page. There is wiring diagrams and such for hvac system. Might help somehow

 

Here's some voltage checks you can do at the fan relay socket in the PDC.


Set the DVOM to 20 VDC. Use the battery NEG post as ground for the meter.


The important voltage check is at pin cavity 13, which is the relay control coil ground driver from the PCM. When the PCM receives a signal that AC is requested or the coolant temp has reached a preset high temp, the PCM will provide a ground to the fan relay control coil, which pulls in the power contacts in the relay to power the fan.


The low voltages seen at pin cavity 13, with the ignition switch to ON/RUN (engine not running), is what Chrysler refers to as a "live ground". Most other relays have the same live ground. If there is no voltage reading with meter set to 20 VDC switch to 2 VDC and see if you pick up a voltage. If no voltage is present I would think the driver wire from PCM connector C3, pin C2 is open or the PCM internal driver circuit is dead.


Edit: Checking relay input voltages with the relay removed and the ignition switch to ON/RUN will trigger a CEL: DTC P1491, Rad Fan Control Relay. Clear the DTC with a code reader or scanner.



.
The ground for the fan is at G106, which is at the left inner fender, next to the PCM. See pic.



.

 

Thanks guys - good info. Short story - I'm an idiot. NM-XJ was right - looked at the fan fuse again and realized it was blown. The lack of burn marks, the embossed "copyright fuse brand name", and multiple neck points led me to a bad call. New fuse installed = fan works => but still not sure what temps drive the fan to turn on. My summary:
Personal Experience
- '96 4.0L XJ => e-fan turns on w/ 'some' temp (8-10 minutes idle, A/C off) - assume coolant temp
- '98 4.0L XJ => e-fan always on w/ A/C. Fan off up to 230 F coolant. Fan did run after driving today (95F ambient + 210F coolant) - but turned off after idling 3-5 minutes w/ A/C off. Shot IR gun at trans fluid lines - ~175 F but fan turned off right after taking temp so I don't know if temp was falling.
Other Forum Posts:
- 2000+ => based on A/C head pressure w/ coolant temp >230F

CCKen - thanks for the pin-out. Your comment about the DTC worried me because I did not have an engine light after pulling the relay and checking pin-outs with the engine running. Pulled codes and P1491 was present. Cleared it, but it returned next key cycle - fan still works. For now I'll try to forget that detail and just drive it. At least now I have re-created everything that drove temps to 240+F and it has stayed at 220-230.

 

I have a 96 XJ Sport, and the fan comes on at 221 F (just happened to be monitoring this yesterday). I suppose it could have been that it remained at or above 220 F for a set amount of time that triggers it, but I doubt it is that sophisticated.