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Cooling fan will not turn on?

Tiny
AMANDA STAEGE
  • MEMBER
  • 2003 JEEP LIBERTY
  • 3.7L
  • V6
  • 4WD
  • AUTOMATIC
  • 159,000 MILES
Vehicle listed above is the Sport model. My cooling fan absolutely refuses to kick on by itself. I have code P1491 on with the check engine light. So far we have replaced; the relay (and mounted it higher so that it won't get corroded so easily again) and the ECM. The fuses are all good, the fan motor works when you run power directly to it, jumping the cooling sensor doesn't tun the fan on, and the temperature gauge works. Does anyone have any other suggestions at all? Every time we have tried to get it to run we let it heat up for a bit so that it's over the center line on the gauge. I'm just frustrated because there's nothing else mechanically wrong with it and it's summer now so I worry about it overheating more easily. Please help if you have any suggestions at all! Thank you so much!
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Sunday, June 14th, 2020 AT 3:09 PM

18 Replies

Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 108,128 POSTS
Hi,

This is one you will need to work backwards with. First, start at the fan. There should be two wires to it. The yellow wire is the power supply. Check it for continuity between the motor and the relay. Also, confirm there is power to the relay via fuse 2 (40 amp). I highlighted the wire I am referring to.

The black wire with an orange tracer is ground. Check for continuity to ground there as well. Make sure to move things around to see if it is a bad connection.

Let me know what you find.

Joe
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Sunday, June 14th, 2020 AT 4:05 PM
Tiny
AMANDA STAEGE
  • MEMBER
  • 3 POSTS
Hi, we just checked it. The ground is good, there’s power to the relay, there’s continuity to the fan motor and the relay. Any other suggestions?
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Monday, June 15th, 2020 AT 12:16 PM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 108,128 POSTS
Hi,

Okay, that is a good thing. Now we need to go through the diagnostics to determine the break down. The only other thing you could check easily is if there is a pulse signal between the power-train control module (PCM) and the relay. If there is, then we have a wiring issue at the relay. The only way I know to check for that pulse signal is via a live data scan tool.

Are you certain nothing was damaged at the relay when you changed it's location? Does the fan turn on if the A/C is turned on? Also, the fan will not be actuated until 210° F, is it reaching that when you checked it?

____________________________

If you look at the two pics below, they are the flow chart for diagnosing this code.

Here is a list of possible causes:

SYMPTOM
P1491-COOLING FAN RELAY CONTROL CIRCUIT

POSSIBLE CAUSES
- Radiator fan relay operation
- (C24) fused B+ output circuit
- (Z212) ground circuit
- (K173) radiator fan relay control circuit open
- (K173) radiator fan relay control circuit shorted to ground
- PCM

_____________________________________
If you notice in the possible causes, you have already replaced the relay, we know there is power to the relay, we know the relay ground is present, so now we need to determine if the control circuit is shorted to ground or if the signal between the relay and fan motor is open (broken).

Let me know if you are comfortable checking the things listed below. If you have questions, let me know that as well.

Joe
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Monday, June 15th, 2020 AT 8:20 PM
Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
  • 42,833 POSTS
Can you start the car and turn the A/C on will the cooling fans come on after about 2 minutes? The P1491 code will have nothing to do with it.
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Friday, June 19th, 2020 AT 12:34 PM
Tiny
AMANDA STAEGE
  • MEMBER
  • 3 POSTS
Nope, cooling fan doesn’t come on with the /AC on. We tried another relay to see if ours was bad out of the box, still nothing. It’s currently at a new shop trying to see if they can figure it out. :(
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Friday, June 19th, 2020 AT 1:06 PM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 108,128 POSTS
Hi,

I have a feeling it is either the an open between the relay and the motor or between the module and the relay. If you could, let us know what is found.

Take care,
Joe
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Friday, June 19th, 2020 AT 6:43 PM
Tiny
WAHOOS
  • MEMBER
  • 5 POSTS
  • 2002 JEEP LIBERTY
Engine Cooling problem
2002 Jeep Liberty 6 cyl Four Wheel Drive Automatic 100k miles

02 jeep liberty fan will not kick in. Fan works when jumped to 12v source so fan is good. It all started when 4 pin wiring harness that connects to relay had burnt up. Looks like the harness connector was arcing @ the relay connection. I replaced harness with kit from chrysler. Didn't fix the problem. Replaced relay thinkin it could be bad. Still not workin. 40 amp fuse is good so I'm not sure what to check next. I'm an electrician so I have tools and skill to check things. Just don't know what to check next. Any suggestions would be great.

Thanks in advance
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Thursday, January 28th, 2021 AT 9:25 AM (Merged)
Tiny
BLUELIGHTNIN6
  • MECHANIC
  • 16,542 POSTS
I have posted below the entire cooling fan wiring circuit to help you.. since the relay , fuse, wiring and fan have been ruled out..all that leaves is the computer (PCM), but you can take a look at the circuit for yourself below..


https://www.2carpros.com/forum/automotive_pictures/261618_Noname_2369.jpg

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Thursday, January 28th, 2021 AT 9:25 AM (Merged)
Tiny
WAHOOS
  • MEMBER
  • 5 POSTS
Thanks for the diagram, it helped me troubleshoot a little more. I was hopeful for a bad splice on the harness but I put a jumper between the power pins and the fan worked. I got continuity from ground pin and frame so that was good. ReSpliced pcm wire to make sure. But still doesn't work. I don't know how to further check pcm so I guess I'm stuck replacing the unit.
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Thursday, January 28th, 2021 AT 9:25 AM (Merged)
Tiny
WAHOOS
  • MEMBER
  • 5 POSTS
Is there anyway to find a pcm pin out diagram for 02 liberty limited? I pulled the pcm connector out and checked for continuity between connectors and got nothing. I would like to know which pin it is so I can run new wire from pcm pin to wiring harness.
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Thursday, January 28th, 2021 AT 9:25 AM (Merged)
Tiny
BLUELIGHTNIN6
  • MECHANIC
  • 16,542 POSTS
Hello,

Yep I have a guide that will help you.

https://www.2carpros.com/articles/how-to-check-wiring

Here are the engine wiring diagrams for the PCM (below)

Please let us know what happens.

Cheers
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Thursday, January 28th, 2021 AT 9:25 AM (Merged)
Tiny
WAHOOS
  • MEMBER
  • 5 POSTS
I found A light green wire in the pcm wiring connector but it must be a different wire. I cut into the split tubing to trace it but it does not tie into the the fan relay.
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Thursday, January 28th, 2021 AT 9:25 AM (Merged)
Tiny
WAHOOS
  • MEMBER
  • 5 POSTS
So I'm still trouble shooting this fan in hopes of not replacing the pcm and to make sure that is indeed the problem before I purchase a new one.

So here is where I stand now. I pulled the conn from the coolant temp sensor (cuz something has to tell the pcm when to start the fan. Right?) And I jumped those two wires. Fan comes on soon as start the jeep. Gauge doesn't read but fan now works. Well I replace that sensor but that damn thing still doesn't come on! How could that be?

Any suggestions would save my hair from being pulled out :-) thanks
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Thursday, January 28th, 2021 AT 9:25 AM (Merged)
Tiny
HOUSTOIB
  • MEMBER
  • 1 POST
The fan is not supposed to turn on until the engine reaches 170 degrees, so it shouldn't turn on when you start up the jeep. Are you waiting until the jeep gets hot?
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Thursday, January 28th, 2021 AT 9:25 AM (Merged)
Tiny
STEVE W.
  • MECHANIC
  • 12,941 POSTS
If your Liberty is anything like mine that fan may not come on until a good hot summer day. Mine doesn't come on at ALL if the outside temperature is below 75 or so.
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Thursday, January 28th, 2021 AT 9:25 AM (Merged)
Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
  • 42,833 POSTS
It sounds like you still have a bad engine coolant temperature sensor or the ECM is bad.
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Thursday, January 28th, 2021 AT 9:25 AM (Merged)
Tiny
SIMPUB
  • MEMBER
  • 2 POSTS
I have a very similar issue. I have replaced the entire A/C system, but it won't power. If you apply direct current to it, the compressor comes on and cools. At the same time, my engine/radiator fan will not come on, even when extremely hot, so the coolant boils over, mostly when idling. However, the fan will come on when I apply direct voltage to it.

I don't see any fuses out. I tried swapping relays to test. Also, I temporarily swapped in another dashboard control unit from another Jeep to see if that was the issue.

So far nothing works. Still driving without A/C and avoiding overheating by keeping the Jeep moving.

Does the combination of these two issues point to anything specific? It would be awesome to have A/C finally!

Thanks!
Mark
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Tuesday, July 26th, 2022 AT 5:15 AM
Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
  • 42,833 POSTS
Yep, A/C is nice in the heat. Let's check for power at system systems seven fuses.

Here is a wiring diagram to show you which ones and a guide to show you how to check for power:

https://www.2carpros.com/articles/how-to-check-a-car-fuse

Check out the diagrams (below). Please let us know what you find.
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Wednesday, July 27th, 2022 AT 12:23 PM

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