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Discussion Starter #1
Search didn't reveal much on this so I'll ask the question.

2002 Durango R/T 5.9, AWD

Electric fan not coming on with AC switched on. Everything tests out OK but no signal is making it to the relay from the PCM...not getting a gounded signal from the PCM at the relay's socket pin.

Temp is in the 60's now so I was wondering if the PCM also needs a high air temp signal as well as AC "on" to turn on the fan. I can wait until hotter outside temps in the spring time to test this theory but would prefer to know now if I have a bad PCM.

Thanks.
 

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Turbo Dakota Junkie
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Mine did the same thing, but my answer was to just go ahead and add another relay and get the signal from the key-on hot wires. I've completely removed my mechanical fan.

Key on = fan on and let the thermostat control the temp of the water from there. It's WAY cheaper than another PCM or the time I would have spent trying to figure out why it wasn't working the "right" way.
 

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If it isnt the relay it might be the fan itself. Mine went out and wouldnt run but if you spun it by hand it would then start up. This was of course without a clutch fan to cut my arm off.
 

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Discussion Starter #4
Mine did the same thing, but my answer was to just go ahead and add another relay and get the signal from the key-on hot wires. I've completely removed my mechanical fan.

Key on = fan on and let the thermostat control the temp of the water from there. It's WAY cheaper than another PCM or the time I would have spent trying to figure out why it wasn't working the "right" way.
Yeah I have thought about this as a fix. I would just add a wire from the AC clutch wire to the fan itself.

But I really want to know how the PCM is programmed to understand if what I'm seeing is normal.

If temp itself will turn on the fan, it should be good enough. The AC still works fine right now without the electric fan. In hot weather, AC will be on and if temperature turns on the electric fan then the AC will still work at idle (no MPH).
 

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Turbo Dakota Junkie
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The electric fan isn't supposed to come on until after the pcm sees something like 210° or 220° if it's just for cooling. I guess you could let your idle with something blocking the radiator off and see if the fan kicked on after the temps got up there.
 

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Discussion Starter #6
If it isnt the relay it might be the fan itself. Mine went out and wouldnt run but if you spun it by hand it would then start up. This was of course without a clutch fan to cut my arm off.

LOL - yes I guess that would be a bloody mess wouldn't it?

At the end of last summer I troubleshot down to a bad fan motor. So I just got around to replacing it this weekend. It was bad for sure...didn't run with a direct battery supply.

Now, if I remove the relay and jumper the socket pins, the new fan goes on fine. The circuit has constant power with key off.

Relay itself is fine because I swapped it with the PCM relay right next to it (same ones) and the car still starts. Pulled it out and the car died.

Ohm out the circuit from the PCM to the relay and I get some 5 mega ohms...it's not an open loop or cut wire. With the car running and AC on, this circuit should be a direct ground but it's the same mega-ohm reading. So that's why I know the PCM is not grounding out it's solid state gate on the chip. "Why not" is the question.
 

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The electric fan isn't supposed to come on until after the pcm sees something like 210° or 220° if it's just for cooling. I guess you could let your idle with something blocking the radiator off and see if the fan kicked on after the temps got up there.

Yes but what about AC "on". I throught the fan should go on anytime the AC is on. If not OK, the operation is normal. That's what I'm trying to answer.

I did jumper the air intake sensor pins to drive air intake temp through the roof but the fan never kicked on. (Did through a nice over temp code though.) I couldn't get to the water temp sensor so I didn't get to test this "high" input to the PCM. I suspect it's just the water temp that drive the fan and not air.
 

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Turbo Dakota Junkie
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Mine seemed inconsistent and my factory relay would overheat at times during the hot months. No problems now since the factory relay has zero load on it. I started to look for "why" it was acting up, but decided the workaround was a much better use of my time.
 

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Discussion Starter #9
I popped in the repair manual I have on CD for this Durango when I got home tonight and found several conflicting references to the PCM control of the electirc fan with the AC switched on. Some said that anytime the AC is on the fan will go on. One section said this wher both AC on and high temp is required to turn on the fan:

"The relay is energized when the coolant temperature
is above 80° C (176° F) or battery temperature
sensor above –12° C (10° F) or air conditioning is
selected and coolant temperature is above 95° C (
203° F) or air conditioning is selected and battery
temperature sensor is above 41° C (106° F).
The fan is then de-energize when coolant temperature
drops below 82° C (180° F or battery temperature
sensor below –9° C ( 16° F) or when air
conditioning is selected and coolant temperature is
below 92° C (198° F), or air conditioning is selected
and battery temperature is below 38° C (100° F)."

This is very strange. I guess then if I let the coolant get to 176 F the fan kicks on and then if I hit the AC, the fan turns off until the coolant gets to 203 f or if between 176 and 203 F I turn off the AC then the fan will go back on.

I guess I'll just wait for warmer weather and see what happens. I'm not sure this thing will get too hot at all right now, even in Phoenix.
 

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For the record, I had (actually stiil have) the very same problem; I can't get my fan to come on with the A/C "on" method and the car overheats at idle. After testing the relay, both fuses (hi and low V sides) and replacing both the PCM and the fan, I gave up and ran a jumper from relay pin 86 to the battery negative terminal. This turns the fan on (using the relay so the ground wire can be light, I used 16G copper) whenever the key is in the "on" or "start" position. It means sitting in the car listening to the radio is going to drain the battery fast since the fan's always on. UPDATE: This is wrong. Using pin 86, the fan is only engaged in the "start/run" ignition position, not in the ACC (accessory) position. So I can still sit in the car with the stereo on and not drain the battery.

I have a call in to the outfit that gave me the replacement PCM (the one that didn't fix my problem) to see if they have anything useful to say on the subject. According to my manual the fan relay control signal comes out of pin 17 on the white (center) connector block on the PCM, but I can't find anything that shows me where it comes in to the PDC. Unless I can find both ends it's pretty hard to ring out the problem with the usual tools, so I guess I'm stuck with a hacked up fan controller for the duration. It appears the PCM is somehow putting a constant 5+V on the control pin at the relay block.

This is what I see at the relay with the key on, ignition off (koeo), A/C in the "Max A/C" position:

Pin Relay Circuit Voltage
---- -------------- --------
1 85 12V
2 86 5V
3 30 12V
4 87a 0V
5 87 0V

If I understand the theory of operation correctly (which is a very large assumption) I should see a solid ground on relay circuit 86; this should fire the relay and connect a 30amp fused 12V signal to relay circuit 87, which powers the fan. To prove this theory I directly connected pin 86 to the negative poll of the battery, sure enough the fan fires right up when the key is turned to "on". Position of the A/C selector is unimportant with this kludge; if the key is on, the fan is on.

The odd part is the wiring diagrams show pin 86 tied to fuse #9 , a 10amp fuse in the dashboard fuse box (left of steering column). From what I see, it should have a 10amp fused 12V signal on it all the time. It doesn't of course and I can't figure how it could ever work right if it did. Even more confusing is the same wire supposedly connects to pin 86 on the Fuel Pump relay, but that pin shows 0V koeo. If the wiring diagram is correct, both of these pins should have the same potential on them. They don't, so something is not right in the state of Denmark.

This whole thing is way too peculiar and I've read lots of reports from people having this same problem. The only thing I can think of is there's something wrong with the way the PCMs on these vehicles are programed, maybe something wrong with the way they were wired originally, and there's a whole batch of them running around the country with messed up fan relay controllers. For now, I can't find any way to fix it.
 

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For me this issue is causing the engine light to stay on and i can't get it smogged.....any suggestions around this one????
 

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01 DAk 4.7, but when I start it in the AM with the defroster on, the fan kicks on. Engine is dead cold. Defrost uses the AC compressor to dry the air blowing on the windshield. Not sure if the 5.9 has similar programming, but my Equinox, Outback and Bonneville do the same.
 
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