2005 Elusive Fan Relay Module

[eric1514]

The electric cooling fan on my Jeep isn't acting right. I don't have the heavy duty cooling.

When I turn on the A/C, the fan doesn't come on. The fan motor works. I've run 12v across the pins on the connector and got it to spin, but it won't run on low and it only runs for a second on high.

I suspect the fan control module thingy and not the two square relays in the fuse box. I've watched YouTube videos on replacing it and it's located on the driver's side down low. Mine, if I have one isn't there. ChatGTP says it's on the passenger side behind the headlight or up under the bumper. Before I start ripping the facia off the car, can anyone confirm its existence and possible location?

Also, everyone seems to replace it with Dorman part number 902-310, but this part number is not correct for a 2005. Help.

TIA,
Eric

 

[seafish]

Would be good to know your exact year and engine.

NOT sure about the "fan control module" that you are referring to, as on my 2005 Liberty CRD, the electric fan is controlled by the 2 fan relays (low/high) located in the fuse box above the drivers side headlight.

 

[eric1514]

Sorry. It’s a 2005 Limited with the 3.7l gas.

Supposedly, there is a fan control module sometimes referred to as a relay in addition to the two relays in the fuse box labeled High and Low. I’ve seen people replace it on 2002s and 2003s but it could be it doesn’t exist on 2005s. I sure can’t find it. I think it’s duties have been taken over by the PCM, but I could be wrong.

Basically, my electric fan won’t turn on with the A/C and switching relays around doesn’t help. I’ve jumpered across the relay socket and can get the high speed to run but not the low speed.

Don’t know where else to look.

Thanks for your reply.

 

[seafish]

I’ve jumpered across the relay socket and can get the high speed to run but not the low speed.

On my 2005 CRD, I was surprised to learn that fan engages at high speed only when BOTH relays are engaged.

ALSO, the difference in fan speed between low and high is negligible…IIRC about 300 RPM.
Its actually difficult to hear the differnece, but I used a cheap RPM tool to verify that there was a difference between having 1 fan relay jumpered and both relats jumpered … the high/low markings on the fuse box do NOT matter. Again, this is on my 2005 CRD so YMMV.

Maybe try jumping both relays at the same time and see if that fixes your problem.

 

[eric1514]

I jumpered the hi relay and the fan ran. I simultaneously jumpered the lo and the fan didn’t change speeds. I figure the fan is ok and the relays are ok. That only leaves the elusive fan control module, that I’m coming to believe doesn’t exist, or the PCM. I’ve run out of idea and know how.

 

[seafish]

I simultaneously jumpered the lo and the fan didn’t change speeds.

How did you determine that the fan didnt actually change speeds?

 

[eric1514]

By ear, corroborated by my wife.

I jumpered the hi from pin 30 to 87 and the fan turned on. I then jumpered the lo with hi stilled jumped and there was no change that I could discern. I did this with key off-engine off, key on-engine on, and with the engine on and the A/C turned on. No difference in all three attempts. Also, nothing happens when only the low is jumpered, but I read somewhere that that is how it works.

If I put the relays back in, with the engine running and the A/C on, the fan will kick on for about 1 sec every minute or so. Using a stethoscope, I determined it is the high relay that is clicking on and off.

 

[JeepJeepster]

My 2004 just has relays, no module. Pretty sure its just an 02-03 thing.

Is the A/C compressor staying on during all of this? Or is it cycling?

Be careful jumpering both lo and high at the same time, that'll most likely burn up the fan motor. I would need to look at a wiring diagram, but I would bet it kicks off which ever relay when the other is on.

You need to get a wiring diagram and see whats going on between the fan and the low relay that you're jumpering.

 

[seafish]

I then jumpered the lo with hi stilled jumped and there was no change that I could discern

Like I said, I couldn't hear the 300 RPM difference between hi and lo speed either.

I suggest that you buy an inexpensive photo tachometer and check again rather hten trying to replace an elusive module that might cost more then the tachometer.

Something like this —

You must be registered for see images attach

 

[seafish]

Be careful jumpering both lo and high at the same time, that'll most likely burn up the fan motor. I would need to look at a wiring diagram, but I would bet it kicks off which ever relay when the other is on.

Must be different on the 3.7 … on my 2005 2.8 CRD., thats just the way it works.

 

[eric1514]

My 2004 just has relays, no module. Pretty sure its just an 02-03 thing.

I think you're right.

Must be different on the 3.7 … on the 2.8 CRD., thats just the way it works.

I read about doing this in some old post I found here while researching before I joined this forum to ask my question.

The pigtail on the fan has 3 pins. Connecting the center to negative and one other pin to positive makes the fan run. Hi or Lo, I don't know. If i connect the center to negative and the other pin to positive I get nothing. Is this a valid test of the fan?

 

[seafish]

The pigtail on the fan has 3 pins. Connecting the center to negative and one other pin to positive makes the fan run. Hi or Lo, I don't know. If i connect the center to negative and the other pin to positive I get nothing. Is this a valid test of the fan?

Not sure … on my 2005 CRD, I simply used a bent paperclip to jump terminal #30 (constant battery power) to terminal #87 (output to device ie fan) in the fuse box right where the fan relay plugs into.

I then checked fan rpm with the photo tachometer.
I then jumped the second relay the same way, and the fan speed increased by about 300 rpm.

Again, your truck being a gasoline powered 3.7. might well operate differently.

 

[eric1514]

I did exactly that. I jump 30 and 87 on the hi side and the fan runs. Jump 30 and 87 on the low while keeping the hi jumped, changes nothing. Jumping just the lo does nothing. I tried the same thing at the fan to bypass and relays and PCM control and the same thing happens. One set of pins runs the fan, the other set does nothing. I didn't try hooking up all three. Kinda scary and sparky when you slip.

I think tomorrow I'm going to put a light on the harness going to the fan at the fan and see if there is power going to the fan then the A/C is turned on. Then I'm going to run down to the junkyard with a motorcycle battery and some jumpers and test some fans to see if they act like mine. I'm beginning to suspect the fan and not the PCM.

 

[seafish]

. Then I'm going to run down to the junkyard with a motorcycle battery and some jumpers and test some fans to see if they act like mine. I'm beginning to suspect the fan and not the PCM.

sounds likea good idea.

 

[eric1514]

Thanks for your help. I'll keep you posted.

 

[eric1514]

OK. New day. Out in the garage. I've disconnected the fan at the short pigtail coming off the fan. I've got a test light hooked up to the negative battery pole.

Started the engine and turned on the A/C. Probing the harness coming from the power distribution box to the fan, the dark blue wire which is the low speed fan goes hot and turns on the light steady. Probing the green wire, the high speed, it lights up now and then. If I plug the connector back into the fan, the low speed doesn't run but the high speed turns on and off. So relays and PCM are giving the fan a signal to run, it just won't.

Jumping 12v across the fan connector, confirms this. I can only get the fan to run off the green (high) side when directly connected to a battery.

At this point I'm thinking the low speed side of the fan is dead. I don't know how 2 speed motors like this work, but I don't know what else it could be. If the weather warms up and the ground dries up, I'll take a small battery and some jumpers to the junkyard and test some fans. If I find one that works on both speeds I might buy it. Problem is, they'll want $30 for a 20 year old one and a new one from Rockauto is about $80 delivered.

 

[JeepJeepster]

This is the wiring diagram for my 2004 fan. Ive never had to diagnose my fan, so idk if its accurate. Im around 90% sure that jumpering both the high and low speeds at the same time will burn up the windings in the fan motor. I would need to do some checking to be 100% sure, but thats normally how different speeds on motors work. If youre for sure getting power to the fan when you jump the low speed relay and the fan isnt coming, its gotta be a bad fan motor.

Now that I see this, Im very curious to check if the relays are actually protected by the same 40amp fuse as the fan itself. If so, thats wild.

Just an interesting fact since we're here. The PCM will turn on the electric fan when the transmission gets somewhere around 220F, even if the A/C or engine are not calling for it. Ive never been able to find this in writing anywhere, its just an observation.... And I think its only the low speed, Ive never had the high speed kick on for just the transmission.

You must be registered for see images attach

You must be registered for see images attach

 

[seafish]

This is the wiring diagram for my 2004 fan. Ive never had to diagnose my fan, so idk if its accurate. Im around 90% sure that jumpering both the high and low speeds at the same time will burn up the windings in the fan motor. I would need to do some checking to be 100% sure, but thats normally how different speeds on motors work. If youre for sure getting power to the fan when you jump the low speed relay and the fan isnt coming, its gotta be a bad fan motor.

Now that I see this, Im very curious to check if the relays are actually protected by the same 40amp fuse as the fan itself. If so, thats wild.

Intuitively you are correct, but practically that is exactly how the electric fan on my 2005 CRD operates.

 

[seafish]

This is what my local AI says about it when I asled—

"can a single 12v electric cooling fan have two separate windings each activated by a separate relay to control speed?"


Yes, a single electric cooling fan can have two separate windings—each controlled by its own relay—to operate at different speeds (low and high). This setup is common in dual-speed fans, where one winding powers low-speed operation (e.g., triggered by normal temperature rise or AC engagement), and the second activates high speed when additional cooling is needed (e.g., high engine temperature or elevated AC pressure). Each winding connects to a dedicated relay, allowing independent control and preventing overload.

The key is using a dual-wind motor specifically designed for this purpose. Standard single-winding fans cannot achieve true dual-speed control this way.

Step-by-step instructions​

• Ensure your fan is a dual-speed type with three wires: common (positive), low-speed, and high-speed terminals.
• Mount the fan securely near the radiator with proper clearance.
• Install two relays in a dry, heat-resistant location; label them “Low Speed” and “High Speed.”
• Connect the fan’s common positive wire directly to the vehicle battery via a fused circuit (use 14–16 AWG wire).
• Wire the low-speed terminal to the output (terminal 87) of the first relay.
• Wire the high-speed terminal to the output (terminal 87) of the second relay.
• Connect terminal 30 on each relay to a constant 12V power source with individual fuses.
• Connect terminal 86 on each relay to switched ignition power.
• Connect terminal 85 on the low-speed relay to a temperature switch or AC signal that triggers at moderate heat.
• Connect terminal 85 on the high-speed relay to a second temperature switch or trinary AC switch that activates under higher demand.
• Ground both relays properly (terminal 87a or chassis ground as per design).
• Test the system: fan should run at low speed when engine reaches normal operating temperature or AC is turned on, and switch to high speed

 

[eric1514]

Speaking of AI

When this whole situation started and before I joined this forum, I disconnected my fan and ran power to the pins on its connector. I could only get it to run with one set hooked up. I asked ChatGTP if this was a valid test of a radiator fan on a 2005 Jeep Liberty (I was specific) and chat responded "no". It said that there were resistors involved to create the low speed rotation. It said to test it properly, I would have to run 12 volts to the hi side and 6-9 volts simultaneously to the lo side. I'm not able to do that so I assumed the fan was good and started looking for the remote relay/module, which I now believe doesn't exist after 2003.

A few days later, I asked Grok how to test my two speed fan and it said to supply 12v to the ground pin and either other pin. One set would be hi and the other lo. It should run with either set connected. That left me confused.

The weather here has been dismal so no trips to the junkyard to test other fans. Later today I will try to rig up two test lights to see if the fan is supplied voltage to both speeds simultaneously. I suspect it is.

I'll be back.

This is the wiring diagram for my 2004 fan...

Thanks for that.

P.S. How come I'm not allowed to quote other folks at the push of a button. I have to do it manually using script?