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99 XJ electrical fan issue

Scotts99XJ

NAXJA Forum User
Location
Utah
Ok... I have a question.... I just purchased a 99 XJ about 4 days ago. Completely stock (for now). I am new at the whole XJ world and this forum. Question is: When I start the XJ warm or cold, A/C is off, the electric fan cycles on and off immediately and cycles constantly, is this normal?
Lately it has been in the 20's here and even starting it cold the fan starts cycling as soon as the motor kicks over.
 
No that is not normal. Has it been customized, or stock? If not you might check the fan relay, see if is sticking, going bad for starters.
 
You don't have the defrost on either, correct?

The defrost will kick it on and depending on ambient / under hood temps, it could create that cycle pattern..
 
It is completely stock. I have only had this XJ for a week or so. Defrost is off also. Starting it cold the E-fan starts cycling immediately.
 
If the Electric Fan was on steady I would suspect that the fan relay power contacts were welded closed, but that your fan cycling on and off may indicate a defect in your HVAC system. The PCM thinks you've called for AC or Defrost and has provided a ground to the control coil of the fan relay. If this is the case, you AC compressor clutch should have engaged.

Are you familiar with the AC Compressor in this vehicle? The reason I ask is, that you should look to see if the clutch has engaged while the fan is cycling on and off. If it is you would need the proper wiring diagrams to troubleshoot it.

This should be resolved because the Radiator Electric Fan also activates when the engine coolant temperature gets to 218*F +/- to protect the engine. Deactivating the fan by pulling the 40 Amp fan fuse in the PDC to make the fan stop running would deactivate this feature. Bad Ju Ju.

BTW, does your coolant temp indicator in your instrument cluster work okay? Are you having engine performance problems?

The fan overtemp protection, temp indication, and engine performance functions all go through the engine coolant temperature sensor on the thermostat housing. Do you have a Check Engine light on?
 
If the Electric Fan was on steady I would suspect that the fan relay power contacts were welded closed, but that your fan cycling on and off may indicate a defect in your HVAC system. The PCM thinks you've called for AC or Defrost and has provided a ground to the control coil of the fan relay. If this is the case, you AC compressor clutch should have engaged.

Are you familiar with the AC Compressor in this vehicle? The reason I ask is, that you should look to see if the clutch has engaged while the fan is cycling on and off. If it is you would need the proper wiring diagrams to troubleshoot it.

This should be resolved because the Radiator Electric Fan also activates when the engine coolant temperature gets to 218*F +/- to protect the engine. Deactivating the fan by pulling the 40 Amp fan fuse in the PDC to make the fan stop running would deactivate this feature. Bad Ju Ju.

BTW, does your coolant temp indicator in your instrument cluster work okay? Are you having engine performance problems?

The fan overtemp protection, temp indication, and engine performance functions all go through the engine coolant temperature sensor on the thermostat housing. Do you have a Check Engine light on?

I have no CEL and temperature appears to be normal. I have no engine problems. Could it be the "engine coolant temperature sensor"?
 
I have no CEL and temperature appears to be normal. I have no engine problems. Could it be the "engine coolant temperature sensor"?

Maybe, sort of...

I believe your 99's fan is controlled by the PCM in all aspects. In other words, the CTS combo sensor feeds data to the PCM and it triggers the efan based on its interpretations of that data. Same for the A/C, it provides input to the PCM and the efan is controlled by the PCM.
 
If you have the heater controls set to blow on the windshield (defrost mode) the a/c will cycle and along with that so will the e-fan. Perfectly normal.
 
Some good suggestions:
- Test pressure switches on A/C that call for the e-fan
- A/C system overall condition
- Check for faulty relays
- Test or replace the Coolant Temperature Sensor
- Climate control selector settings or malfunction. Is the A/C compressor runing ?
 
I have no CEL and temperature appears to be normal. I have no engine problems. Could it be the "engine coolant temperature sensor"?

I think that if the Engine Coolant Temperature sensor (ECT) was defective, you would see erratic temp indications and the engine would run rough (at minimum), and there's a possibility that you would get a CEL.

Try to isolate a portion of the AC system by detaching the Low Pressure Cycling Switch connector and see if the fan continues to cycle on and off. Tell us what happens.

The pic below shows the LPCS connector being jumpered for a different test (disregard). The switch is mounted on top of that black cylinder (AC Accummulator).

Copy5ofCopyofXJACLOWPRESSSWJUMPER.jpg
 
If a CTS is bad (or the wiring...) doesn't the PCM switch to open loop and run smoothly? If so, what does it do with the e-fan? Of course it would also throw a code.

Another option is for the CTS to be reading too high (biased to the high side), and the PCM cycling the fan based on the false high temp readings, which would not throw a code.
 
If a CTS is bad (or the wiring...) doesn't the PCM switch to open loop and run smoothly? If so, what does it do with the e-fan? Of course it would also throw a code.

If the CTS was bad the engine may not run smoothly. In open loop the PCM depends upon sensor inputs (except O2S inputs) including the CTS input. If the CTS was FUBAR'd the PCM may not go into closed loop at all. The PCM uses the CTS input, along with the other sensor inputs, to determine fuel injector pulse width and ignition timing. At idle, the CTS signal to the PCM is the criteria for the PCM to operate at open loop (cold signal) until the coolant temp reaches operating temp (warm signal) where it switches to closed loop. If the CTS failed in such a way at to signal a cold coolant all the time the PCM would remain in open loop regardless of actual coolant temp, demanding richer mixtures; if the CTS failed in such a way as to signal an excessively high coolant temp all the time (above PCM preset value) the PCM may not switch to closed loop. (?)

I've tricked my PCM into thinking the coolant temp was over 218*F (fan settng) by inserting a 470 Ohm resistor in the CTS connector, which drove the temp indication to near 230*F which turned the electric fan on. The engine ran smoothly but I don't know if it went into closed loop or not because I didn't have my scanner hooked up to monitor it. I was just interested in seeing if my PCM would turn the electric fan on if the peset temp value was exceeded.

I'm thinking that the instrument cluster coolant temperature indicator would reflect exactly what the PCM sees for determining open loop/closed loop activity. Always cold indication, always open loop; always [too] hot indication, always open loop. Between 125*F +/- and 218*F +/-indication, closed loop (at idle of course).

Another option is for the CTS to be reading too high (biased to the high side), and the PCM cycling the fan based on the false high temp readings, which would not throw a code.

We haven't heard back from the OP to see if pulling the AC low pressure cycling switch connector had any bearing on his electric fan cycling all the time. Another thread for the dead file I'm afraid.
 
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