Trailer light control module fault and trailer brake control module fault

[Joneii]

Prior to July of 2023 I put hundreds of miles of towing on my ER Lariat with tow package with no issues. Then in July I received 3 OTA updates. They seemed to load without issue although the one that said it was improving DCFC did have to load twice. The next time I towed my travel trailer I got the Trailer light control module fault and the trailer brake control module fault. My right trailer turn signal and brake light no longer work while the truck’s lights are working fine. I checked fuses, but all seemed fine. I hooked the trailer to my neighbor’s GMC and the trailer lights responded perfectly. I took it to the Ford dealer and they initially said their trailer simulator was not working with the Lightning (although it apparently works with ICE models). Then they were able to clear the faults and get it to work with a trailer that they happened to have on the lot. Now they want me to bring in the truck and the trailer to troubleshoot. I will do that, but I’m wondering if anyone else has seen these faults and if so, when and what was the solution?

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[DucMan]

I have had trouble with trailer lights also. A neighbor has a lightning, we tried his also, same thing, the right side lights don’t work. My truck was in the shop for the wiper recall and I asked them to look at the trailer lights. They said everything was working fine on their diagnostic device.

I said that empirical evidence says different: two trucks and the right side lights don’t work on either my utility trailer, or his utility trailer. My GMC Acadia works both trailers lights fine. They said they would escalate with their service representative.

Scott

 

[gern]

I was just towing a rented trailer a couple of days ago. When I hooked up the trailer everything was working fine. A few hours in to the drive the truck threw these fault messages and the right-side light stopped working. I got to my destination, unhooked the trailer, did some errands and charged the truck. When I hooked up the trailer again later that day everything was working fine again. Weird.

 

[Joneii]

Thank you for the replies. It is very strange that all of these trucks seem to have the same issue. It makes me believe there is a software bug out there. I will let my dealer know that this isn’t just my truck and my trailer combo (that is what they suspect). Also, it would be nice if @Ford Motor Company could get some engineers to weigh in on the possible causes.

 

[Joneii]

Just wanted to update everyone. My dealer said I need a new trailer lighting control module and we are waiting on that part. I’ll update again after it is installed and let you know if it worked.

 

[Joneii]

So the new light control module didn’t fix the problem. I replaced one of the trailer led lights and that worked for one trip, but it stopped working shortly after that. The Airstream dealer said that they see this quite often with newer trucks (especially Fords). Apparently the systems are very sensitive and changes in humidity, small amounts of corrosion, etc are enough to upset the system and cause malfunction. I am now trying to find some incandescent lights to “downgrade “ my trailer. Apparently the old incandescent lights work just fine with the newer systems because they draw more current. I’m not convinced anyone really knows what the problem is, but I’m willing to try the incandescent lights if I can find them. I’ll make another post as the saga continues.

 

[Joneii]

Just wanted to let folks know how this issue resolved. I never found the incandescent lights, but it turns out that wires to one of my trailer taillights were actually reversed at a splice further along in the wiring. After this was corrected, the LED lights worked fine. The Lightning is quite sensitive to electrical abnormalities, so it flagged this crossed wire issue, while the older truck just pushed power down the lines and didn’t ask any questions.

 

[hturnerfamily]

I would also suggest that another place to look is the GROUNDING point, both on the Truck and on the Trailer.
GROUND is a primary issue with 12v power, and must be in place, perfectly, for everything to work as wired.
It's amazing how these 'gremlins' come out of the woodwork when a simple ground is not making perfect and total connection.

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