Hello to everyone reading this, I’m new to this forum and need your help! I bought my 2018 Ram 1500 5.7L used and when I got it, it was missing a bunch of fuses. I replaced them all and when I replaced the radiator fan PWM fuse the fans instantly turned on and won’t turn off, even after shutting the truck off. I let the truck sit for 15-20 minutes and it was still on. Any ideas, suggestions, or knowledge is more than welcome! Thank you in advance!

 

Is there a relay that powers the fans? Next big question would be, is it replaceable.......

 

PWM typically stands for Pulse Width Modulation which would usually, when pertaining to motors, indicate a variable speed signal. With that label for the fuse and the fact that the radiator fan is running continuously, it sounds very likely that there is a motor speed controller for the radiator fan that has failed in a shorted condition. I don't have access to a 2018 Ram wiring diagram to confirm this, but that's where I'd be looking if it were my truck. Sometimes the fan's high speed is controlled by a high speed relay so it is possible there is also a fan relay for just high speed that is fed from the same fuse.

PWM control over the HVAC fan is pretty typical but I haven't seen that applied to radiator cooling fans much. Typically high and low speeds are sufficient for the radiator cooling fans. Maybe this is another method for attempting to improve fuel economy by reducing the electrical load on the charging system?

-Rod

 

There is a high speed fuse and a low speed fuse that look like they could also act as relays? I’m not the best when it comes to this stuff. I thought that maybe I had a bad temp sensor, but the idea that it could be a bad fan controller sounds logical. Thank you for your input!

 

I had the same question, so I looked and looked for it, some people said on another site that the relay for it is located near the horn, but I couldn’t find it. I’m at a loss for now.

 

What fuse number and rating was the one that caused the fan to come on full speed? Did it happen to be Fuse 3 rated for 60A in the underhood power distribution box located at the left (driver's side) front of the engine compartment? I'm trying to determine if your 2018 Ram 1500 wiring diagram might be the same as my 2014. I have the cooling system wiring diagram for my 2014 but I don't have one for he 2018.

-Rod

 

I’m currently having this exact same issue with my 2021 1500 Classic 5.7 66k miles. Bought it used and when I replaced the missing 80amp fuse for the PWM the electrical fan runs and doesn’t stop. There’s a relay for both high and low that I swapped out with another identical non vital relay in the box and it had no effect. Fan still running. I’m not seeing any specific separate resistor for the fan motor (unless it’s in the motor) that I can switch out and most videos for replacing the fan with v6 fan just show a wiring harness, nothing else. Temp sensor appears to be working fine (digital gauge and needle rise and fall together). Any help with most common issue to resolve this would be awesome! Thanks

 

Maybe the PWM fuse is optional depending on other features, and if a fuse is installed into that slot it bypasses the high and low speed fan relays? It seems odd that so many vehicles are missing the PWM relay. So with the PWM fuse installed the fan continues to run even with the high and low speed relays removed? Is there a reason you went looking for the PWM fuse, such as your truck was getting hot when driving at low speeds and/or idling? Prior to installing the fuse had you ever heard the radiator cooling fan run? In other words, are you maybe trying to fix a problem that doesn't actually exist?

-Rod

 

Looking over the wiring diagram for the 2014 Ram, the 3.0L Diesel and 3.6L V-6 Rams have a speed sense line on the radiator fan. The 5.7L uses the high and low speed fan relays. The 80A Fuse 1 goes directly to the fan with a note "Except 5.7L" so it is possible that the wiring is complete for Fuse 1 and if you put a fuse in there you power the fan directly rather than through the relay, as intended, for the 5.7L. A quick continuity test with the fan unplugged and the 80A fuse removed could confirm that theory.

-Rod

 

I’m trying to solve an issue where my truck temps just continue to climb while towing my camper (5k lbs) up some short steep grades here in northern AZ. It’s given me the warning (250 degrees I think) while towing. It’s quick to return to cooler temps when I stop or slow but I’m having to slow down to 40mph at 3k rpm. I understand the hemi runs hot and I understand if it climbs and maintains but it just keeps going even after slowing down. My thought was the electric fan isn’t kicking on at 220 however I have seen it kick on when using the AC so I know the low speed works. I saw that the 80amp fuse was missing and figured that was the issue but sounds like maybe not. Is it normal to have to slow down that much when towing what seems to be a rather lightweight trailer? I’m not trying to go 75 up the interstate but 40 seems pretty slow. Thank you so much for the information thus far. It’s greatly appreciated.