I've searched the forums quite a bit, and while I've found some related threads, none of them have lead me to a solution. Apologize in advance if my search-fu was insufficient, however:

I have a 2015 JKU, and this past weekend threw a P0480 code, which is a fault of the Fan Control Circuit. After the code occurred, my Jeep began to overheat while idling in a parking lot, and I have since confirmed the radiator fan is not ever running.

I've learned that for the 3.6L, the fan is controlled by a pulse-width modulated exciter signal from the TIPM. I'm having trouble hunting down the source of the problem, however. Here's what I've done so far:

• I've checked the J19 60A fuse. I have continuity. I've replaced it just in case without any change.
• I've checked the K11 low-radiator-fan relay inside the TIPM, and it opens as expected and has very low resistance, so it seems to be good.
• I also checked the two 56055667AB fan relays near the master cylinder in front of the driver's seat. Though I'm honestly not sure how they are related to the wiring of the fan, but they are labeled as an official mopar part labeled "fan relay". I considered they might be related to the blower fan rather than the radiator fan...
• I've disconnected the harness going into the fan (near the radiator cap) and confirmed it it delivering a solid 12V signal and is grounded (though I can't say with a certainty the ground is super solid; I've seen a couple reports of faulty grounds with the fuse-able link; I'm going to try and double check that).

Where I've gotten stuck is:

• If I jump the fan to my battery by providing 12V, ground, and a 12V direct signal on the PWM exciter terminal, nothing happens (the fan doesn't try to spin). While my first inclination was to think this means the fan is broken, I don't know if the 3.6L fan will actually turn on when given a solid 12V signal on the exciter wire, or if it needs a more specific signal since it's variable based on the duty cycle. Is this a valid way to test the modern fan on the 3.6 JK?
• I've also connected my multimeter up to the exciter terminal and the ground coming from the harness to the fan, and I am never detecting any voltage from the PWM exciter terminal. I've run from a cold start up to 230 degrees with the harness detached and the multimeter in place, and even with "MAX HOLD" on, the multimeter never detected a voltage. I don't know if this might indicate a TIPM issue, or if I'm simply testing the signal wrong. I also don't know if the code has to be reset for it to even try to enable the fan. Is this a valid way to check the voltage from the TIPM for fan control?
• I've looked at the BBB Industries Wiring Diagram, but there is no indication of the external fuses or relays in the system, and there are no schematics for the PWM signal itself.

In short, before I spend money on either the TIPM or the fan replacement, I'd like some way to confirm that both or neither sides are malfunctioning. I'm still missing some piece of the puzzle as to why there are two "high" fan relays on the driver's side of the engine compartment (or if those are even related), as well as a "low" fan relay and the purpose it servers -- especially when there is also an always-on large gauge power line directly to the fan. I would've guessed the PWM is responsible for the variability of the fan speed and any relays would be built into the 400 dollar fan assembly itself - since that's the tradeoff of this designed compared to the 3.8L models.

I've had a friend suggest I should just pay the diagnostic fee for a Jeep dealership to test things, which if I can't get a concrete answer myself is probably what I'll have to do, but if there is anyone with any experience with the later JK cooling system, advice or diagnostic tips would be very appreciated!

Thanks!

 

It sounds like you have done quite a bit of diagnosis already and I haven't personally experienced this problem. I'm unsure what you've already found for diagnosis research but here's what I was able to find.

P0480= Cooling Fan 1 Control Circuit Open.

Everything seems to point to the cooling Fan Relay as being the fault as you suspect for that code, maybe just need to determine the correct relay and location?

Here's some videos I came across with the same code, from other FCA vehicles which I will assume have similar DNA.


Dirt in Fan housing

 

Thanks for the research, I appreciate it!

Yeah, I've run into these videos among others; unfortunately the specific setup on the Pentastar 2013+ is rather specific it seems. 2012 and prior Jeeps are setup with a dual relay setup, where-as 2013 and newer are using this PWM variable speed outrunner setup.

There were some interesting details here: https://wayalife.com/showthread.php/...roken-3-6-help!

In particular:
But, this was followed directly by this:
That leads me to believe it may not be as simple as just jumpering the signal wire to get the fan to run. If it expects a certain pulse width for the duty cycle, there isn't much I can do to "simulate" that.

Unfortunately, I've checked a variety of relays, and have yet to find one that could be a problem. I'm going to check my grounds, clear the code, and try to diagnose again. I'm thinking an oscilliscope may be required to actually diagnose the PWM signal, which is not going to be something I have on hand.

 

I was able to figure out what was wrong, and wrote up the results of my research here for the next person!

https://www.realjenius.com/2018/06/2..._radiator_fan/

 

You should post this as a write-up on the forum! Great job!

 

Great Write-up. One thing of note, since you mentioned you had troubles trying to verify the PWM voltage to the fan due to having a lack of tools. If you know it's a PWM voltage that should be present, then you could have used a Volt meter and put the meter to read AC Volts RMS. The voltage reading won't be 100% accurate, but as long as there is a voltage reading, and that reading is below 14 volts (The DC voltage reading of your battery) with the engine running, then you know you have a PWM present.

For some further insight, here's a measurement I took using my O'scope and probing our JK's headlight PWM. You should notice with my scope I turned on V "mean" to get the average voltage which came out to be 12 Volts, when the BATT voltage was 13.9Volts (ie DC Battery voltage level).


So while a voltage won't be 100% accurate of a PWM using an AC volt meter, taking a measurement with a volt meter should be able to provide you some insight. As well, some multi-meters have a Frequency and Duty Cycle measurement function which could also be used on a multi-meter and you can see what those readings would look like, since I turned those measurements on my scope as well.

Here's a good video that explains the inaccuracies of your readings using an AC volt meter, but that doesn't mean you still can't get some kind of indication that the PWM voltage is present.

 

I’m running into the same issue. I’d like to read your write-up, but the posted link takes you to a website that is no longer available. Would you mind posting your write-up here? Thanks!

 

Sorry about that -- it should be fixed now!

 

After checking everything, I decided to remove the 10mm bolt holding the ground wire and then tighten it back down. The 10mm bolt wasn't loose to begin with and the wire wouldn't budge, but I figured it couldn't hurt. After doing this, the fan started to operate normally. I'm not sure how it lost connection. Thanks for the great write up!

 

Hello my name is crystal i wanted to see if anyone could help me , I just bought my brothers 2016 jeep trailhawk and i have a problem the fan steady runs except when i turned off a/c it stopped but when i brought it to auto zone it gave the code P0480 =cooling fan 1 control circuit open ? So ive read what you had to say that fixed yours and i checked my battery connectios and my postive side is very loose also so im thinking i have same problem as you but my question is how do i tighten it up because mine will not tighten when i try to tighten ??If anyone can help me i would be so thankful ? you can answer me here or my cell 409-658-5098 thank you so much .........