Radiator fan is not performing as it should

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flagtrax

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I purchased a 2006 TJ a few months ago and have been pretty happy with it aside from a few querks. It is a 2.4L 4cyl, with the basic package. I have noticed that (IMHO) the fan is not performing as it should. I have searched the many forums for information and have found out several things. 1. There is much confusion as to how electric cooling fans work. (YES disbelievers, the 2006 2.4L has a factory electric cooling fan. and 2. There is very little information as to how the fan circuit works. Even the factory service manual has gross errors, on one page stating the fan is controled by the ecm, and on another it states it is under control of the pcm. (I have not seen anywhere else in the factory service manual another reference to an "ecm". The wiring drawing of the circuit seems to be in error as well. Let me say at this time I am a retired technician with over 40 years of experience in electronic and mechanical systems. IE: I get it. If anyone has an idea as to what the drawing is supposed to show feel free to enlighten me, but as I see it, it simply won't work as drawn. There is little to no discription of the way the circuit is SUPPOSED to work, which makes it worse. The third thing I might point out, is there are some folks (admittedly trying to help) who offer suggestions that simply arn't correct. For example telling people to bypass or attach jumpers to specific locations can result in a catistrophic failure of a control module resulting in a big buck expenditure. Much of the circuitry in modern automobiles are under the control of control modules which are computers in their own right. The output pins of these can be extremely susceptable to improper voltages and grounds. Without a correct drawing and understanding of how the circuit functions risk is added.

All that being said, I can say that "fundamentally" I understand the circuit as such:
The ETS indicates to the PCM the coolent temperature.
The PCM then determines if the fan is required.
At this point the PCM checks to see if the A/C is active (on) if so the fan should be running
If the fan is needed one of the fan relays is activated. (I really don't know which, the manual offered no help)
The (low speed) relay switches 12v via fuse to the fan motor.
Since the manual drawing appears to be incorrect, I'm taking the stand that it is similar on another lead to the motor. If that is correct, then there are 2 different "feeds" to the motor.
The other side of the motor is tied to ground through a circuit breaker which will trip and auto-reset.
I don't have all my test equipment with me at the present time so I have to take a cautious approach, as I don't want to blow a PCM up. I don't know if the PCM outputs an active low, or high when calling the fan on, and truthfully I don't know if the drawing along with some secret magic would work, since the manual doesn't discribe how it is to work. see attached drawing

Fan circuit.PNG
 
flagtrax said:
I purchased a 2006 TJ a few months ago and have been pretty happy with it aside from a few querks. It is a 2.4L 4cyl, with the basic package. I have noticed that (IMHO) the fan is not performing as it should. I have searched the many forums for information and have found out several things. 1. There is much confusion as to how electric cooling fans work. (YES disbelievers, the 2006 2.4L has a factory electric cooling fan. and 2. There is very little information as to how the fan circuit works. Even the factory service manual has gross errors, on one page stating the fan is controled by the ecm, and on another it states it is under control of the pcm. (I have not seen anywhere else in the factory service manual another reference to an "ecm". The wiring drawing of the circuit seems to be in error as well. Let me say at this time I am a retired technician with over 40 years of experience in electronic and mechanical systems. IE: I get it. If anyone has an idea as to what the drawing is supposed to show feel free to enlighten me, but as I see it, it simply won't work as drawn. There is little to no discription of the way the circuit is SUPPOSED to work, which makes it worse. The third thing I might point out, is there are some folks (admittedly trying to help) who offer suggestions that simply arn't correct. For example telling people to bypass or attach jumpers to specific locations can result in a catistrophic failure of a control module resulting in a big buck expenditure. Much of the circuitry in modern automobiles are under the control of control modules which are computers in their own right. The output pins of these can be extremely susceptable to improper voltages and grounds. Without a correct drawing and understanding of how the circuit functions risk is added.

All that being said, I can say that "fundamentally" I understand the circuit as such:
The ETS indicates to the PCM the coolent temperature.
The PCM then determines if the fan is required.
At this point the PCM checks to see if the A/C is active (on) if so the fan should be running
If the fan is needed one of the fan relays is activated. (I really don't know which, the manual offered no help)
The (low speed) relay switches 12v via fuse to the fan motor.
Since the manual drawing appears to be incorrect, I'm taking the stand that it is similar on another lead to the motor. If that is correct, then there are 2 different "feeds" to the motor.
The other side of the motor is tied to ground through a circuit breaker which will trip and auto-reset.
I don't have all my test equipment with me at the present time so I have to take a cautious approach, as I don't want to blow a PCM up. I don't know if the PCM outputs an active low, or high when calling the fan on, and truthfully I don't know if the drawing along with some secret magic would work, since the manual doesn't discribe how it is to work. see attached drawing

View attachment 138600
Click to expand...
 
Did you ever determine your issue and what the correction is to the wiring diagram?
I also have an electrical background and the wiring diagram will not work as drawn.
Currently working on my son's jeep trying to determine why the radiator fan will not work.
 
Ferg said:
Did you ever determine your issue and what the correction is to the wiring diagram?
I also have an electrical background and the wiring diagram will not work as drawn.
Currently working on my son's jeep trying to determine why the radiator fan will not work.
Click to expand...
Well, ain't that special. I don't know anything about this, but that diagram is obviously wrong.
 
Correct and verified correct 2004 Jeep TJ Cooling system fan schematic is as pasted below.
1639351111505.png

Determined issue is with computer not providing ground to energize either High Speed or Low Speed radiator fan relay when the AC is turned on or via the temperature sensor. Temp Sensor and gauge on the dash function.
Temporary fix until the Powertrain Control Module can be repaired.
Installed a new relay socket purchased from Advance Auto Parts on the side of the Power Distribution Center mounting bracket. Removed the High Speed fan relay from the PDC and installed it in the new socket. Powered the relay via Fuse 11 spare terminal located behind glove box. This terminal is only energized when the Key is in Run. Then jumped the Normally Open contacts from the new relay socket to the terminals for the High Speed Fan Relay socket in the PDC. See following Wiring diagram. i.e. a picture is worth a thousand words. Hope this helps someone else with a similar problem.
1639351657821.png
 
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Hi, I have a 2006 2.4 6spd where the fan won't turn on similar to what was described here. when you experienced this issue, was that the only symptom of your pcm failure? and did you have the pcm repaired or replaced. thank you.
 
Low speed fan when ac turned on.

High speed when engine at temp.

2 speed Fan motor has 4 brushes that wear out,Causing low or high or both speeds not to work.

Check both relays, they are the same so you can swap, but if you leave one out money light will come on.

Never saw issues with pcm before so that’s that. If you turn on ac and fan comes on then that means no issues with the pcm.

bad Temp sensor can cause no fan as a bad ground can as well

Not much to it
 
Thanks for your reply. Fan tested and working, high and low speeds. AC in, swapped relays, no dice. Scanner shows pcm receiving temperature data. Any thoughts on where to look for bad ground?
 
Right off hand, I know there is one that connects block to firewall, check all your connectors on your pcm on the firewall. Just push them to make sure they plugged all the way in, check battery post, check temp sensor connector. It usually take a while for the high speed to come on. Once engine reaches temp it has to go above 210 to kick it on. If it is cold out it might not kick on at all. I will look tomorrow for other grounds
 
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