Cooling fans not working even after replacement?

Tiny
SHAUNALG
  • MEMBER
  • 2018 JEEP CHEROKEE
  • 3.2L
  • 6 CYL
  • 4WD
  • AUTOMATIC
  • 180,000 MILES
Hello,

The cooling fans on my Jeep stopped working recently so I replaced the unit, fans and control module, but the fans are still not working. I would like to test the control module; however I don't know how to do so. Can you offer some guidance? Also, do you have any other ideas of what else could be causing the fans not to work? I traced the cables and verified that that there were no issues. Any advice you can offer is greatly appreciated.
Sunday, April 14th, 2024 AT 1:28 AM

1 Reply

Tiny
STEVE W.
  • MECHANIC
  • 13,236 POSTS
That one has a simple system that is a pain to diagnose without an approved scan tool and security access. There are a couple checks you can do that might give you some direction.
First go to the fan control module and test for batter power at terminal 1 (red wire) in the connector. If that is there the fuse and power feed are OK. Next check that the ground from terminal 2 is good, these vehicles love to have grounds fail. That ground is in the left rear of the engine bay and has a single connection as shown in the second image. You could cheat a bit and splice another wire to it and ground that wire to verify the ground. Now for the harder part. With the key off and A/C off check for power on the blue wire in pin 3. Shouldn't be any. Now find the powertrain control module and connector 1 (this is the one toward the front of the car. Now you need to fin pin 78 in that connector with a Brown wire with a blue stripe. That wire controls the fan relay through the PCM grounding it. To test it you need a simple test light connected to ground and a sewing pin or needle. Use the pin to poke into the wire and contact the metal inside. Now connect the test light to ground and touch the pin. If the circuit is good the relay should turn on and send power to the blue wire on terminal 3 of the fan module. The fans should come on as well. If all those work (take a dab of liquid electrical tape and seal the puncture hole in the wire) the next thing to check would be the temperature sender. But for that you need a scan tool that can show the live data. With that you can look at the coolant temp and unplug the sensor. It should show a large change and in most cases, it will turn the cooing fans on if the ECM has control.

Or use a scan tool and do the testing with it, much easier but more expensive as well.
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Sunday, April 14th, 2024 AT 1:59 PM

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