Running Board Issue and Trailer Wiring Fault when Towing

[scsulliv]

Over the weekend I towed a 7x14 by 8'4" tall vee-nose enclosed trailer on the highway for the first time with my 2020 Expedition MAX. I did 600 miles round trip from Chicago to northern Wisconsin (mostly highway driving). The Expedition has 59,000 miles and the transmission was rebuilt under warranty a few thousand miles ago. I recently had the new PCM reflash / recall performed, too. The trailer probably weighs less than 4000 pounds loaded, but the aerodynamics are absolutely terrible. The good news: The Expedition tows this trailer WAY better than my 2014 Yukon XL with the 5.3L ever did (it's nice towing on the highway at 70 mph with the engine RPM between 2000 and 2600 RPM vs. the 4000+ RPM that I'd get with the Yukon). The bad news? When I stop for gas (which is often - I was getting around 8.6 MPG), the passenger side running board wouldn't fully lower and I get a "Trailer Wiring Fault" warning on the display. Everything works properly once it all cools down. I'm thinking that either some wiring or a module is possibly getting hot from the exhaust heat and causing this issue. Has anyone experienced something like this before? I'm wondering if there is a Ford TSB that might address this issue. Also - the exhaust really booms between 2000 and 2400 RPM, doesn't matter whether the truck is in 7th or 8th gear. Is that normal? It sounds like a chain saw! Thanks in advance!

 

[mx10166]

Sounds like you may have a heat shield that is loose that is making the chain saw sound when you hit that rpm and gear. Sometimes a certain RPM and load crates a harmonic vibration.

If you are getting a trailer fault then you likely have a wiring issue at the trailer. Perhaps there is some excessive voltage being drawn from the trailer that is causing the fault and drawing current from the running boards leaving them with not enough power to fold down. Next time it happens, unplug the trailer and see if they unfold.