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So over the weekend, I towed with my 2015 Ram Ecodiesel for the first time, towing an empty, tandem axle landscape trailer with electric brakes. I had some weirdness happen, and I'm not sure if it is the truck or the trailer or me. The last time I towed this trailer everything worked on the trailer. That was in November with a GMC that I no longer own, but the trailer has been stored indoors, so I don't think anything has changed as far as the trailer is concerned.

First thing I noticed was the trailer running lights won't work. Brake lights, turn signals, and electric brakes checked ok, so since it was daylight, I towed it from my storage hangar to my house. I tried switching from "auto" to "on" with the headlights, and unplugging/plugging/wiggling the trailer connector, but still no running lights.

Next, I noticed my cruise control would not activate, no matter what I did, while towing. Later, once the trailer was removed, the cruise control worked just fine.

The third I noticed: just to see how much of a difference it made, I put the truck in "Tow/Haul" mode, drove a mile or two, then took it out of "Tow/Haul" mode. But, thing is, it acted like it was still in tow haul mode for the remainder of the trip. It would not engage 8th gear at all. At one point, I accelerated to 75 mph, then coasted back to 50, yet the truck would not shift from 7th to 8th. Later, once I disconnected the trailer and took a drive, the truck shifted to 8th just like normal.

Lastly, when I got home from towing the trailer and shut the truck off, for the first time ever I noticed a fan (maybe radiator fan) ran for about 1 minute after the truck was shut off. The outside temp was 45 degrees, and the trailer maybe weighs 900 lbs empty, so I can't fathom that the truck was working all too hard.

So what is going on here?
 

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Ugh I feel for you, sounds like some electronic wizardry.

My bet with the trailer is on a ground.
 

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2015 Outdoorsman EcoD CC w/6.4' 4X4
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For your running lights check the F29 fuse (20 amp FMM). While you have the fuse out, turn the running lights on and check for +12V where the fuse plugs in. If you hae voltage there, put the fuse back in and check for power at the 7 pin plug. People have had issues with the plug coming out of the back of the 4/7 ping plug and the wiring harness that runs behind the front wheel well.
Not sure what's up with the cruise control or the shifting, possible wheel speed sensor.

As for the fan running, check you coolant level, it should be about at the seam in the tank or above.
 

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Discussion Starter #4
For your running lights check the F29 fuse (20 amp FMM). While you have the fuse out, turn the running lights on and check for +12V where the fuse plugs in. If you hae voltage there, put the fuse back in and check for power at the 7 pin plug. People have had issues with the plug coming out of the back of the 4/7 ping plug and the wiring harness that runs behind the front wheel well.
Not sure what's up with the cruise control or the shifting, possible wheel speed sensor.

As for the fan running, check you coolant level, it should be about at the seam in the tank or above.
Thanks for the info on the wiring.

Coolant level is good. Weird that I also noticed the coolant temp was normal before shutting off the truck too (maybe like 201 or so). I should have mentioned that above.
 

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2015 Outdoorsman EcoD CC w/6.4' 4X4
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Coolant level is good. Weird that I also noticed the coolant temp was normal before shutting off the truck too (maybe like 201 or so). I should have mentioned that above.
Coolant temp, oil temp and refrigerant (pressure) all go into running the cooling fan speed.
It might be old school think but any time I tow I'll let the engine idle for about 5 minutes while I disconnect. Similar idle time if I have to pull off and stop the engine.
 

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If HD is as similar to GDE as some say then I bet that is it. Mine is GDE and the fan runs when you shut it off during a regen.
 

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Your tune is holding a lower gear during the regen to keep RPM up. Fan stayed running cuz you shut down during a regen. Both normal.

Sounds like a blown fuse or a short in the trailer wiring. Also check the plug behind the bumper for the 7pin trailer connector, they can be loose.
 

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Mine will not automatically hold lower gears when in regen like described above, no way it would hold 7th to 75.
 

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Mine will not automatically hold lower gears when in regen like described above, no way it would hold 7th to 75.
Are you tuned? Trans tune also?

My truck downshifts at the beginning of an active regen and holds one gear lower than normal. Might be part of the trans tune.
 

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Are you tuned? Trans tune also?

My truck downshifts at the beginning of an active regen and holds one gear lower than normal. Might be part of the trans tune.
My dads 2015 with his GDE tuned ECM and TCM does this as well.
 
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