Hi, I have a 2019 f350 superduty lariat diesel bought it a year ago last October. When I step on the brakes, the cross traffic and bliss system fault, air bag light turns on and cant roll windows down. Radio and hvac settings become inoperable until brake is released.
Also Sometimes it does it with the right turn signal more so than the left causes the same problem. There is also a buzzing sound coming from both led tail light assemblies. I also noticed if I step on the brake, the left side stays on longer than the right side, same issue happens with the turn signal on the left. Anyone have a clue how to deal with this. 2 Dealers looked at it and one did 2 times already with no luck on fixing it. Someone please be smarter than my local dealer on here and have a clue what it could be. (Dealer is blames it on my amber light bar that is connected directly to the battery and not tied in at all with any of the trucks electrical. They might as well blame it on the vinyl graphics causing the issue...)

 

Probably is the graphics. If you have FORSCAN, I'd check there first. If you don't, start with a reset by disconnecting both batteries and let it sit overnight.

 

Numerous reports on this forum of weird electrical problems caused by water/corrosion in connectors located above the spare tire. Recommendation is to un-mate the connectors, dry and clean and then apply dielectric grease to the contacts before re-mating. There are a few connectors above the spare tire that need to be addressed.

 

Definitely check those connectors in the rear, but it could also be a ground issue, sometimes a bad ground gives all kinds of weirdness as things then ground through other devices. When you are under the rear checking all those connections check any ground straps as well.

 

I doubt it’s your lightbar lol. But, funny story.... we had a 2014 Nissan NV as our family van. Great van. A year after we purchased it I swapped the rear brake lights for LEDs. Couple days later the abs system was going wonky.... like pulsating the brakes constantly. Very lightly, but you could definitely feel it, and it warmed up the rotors for sure. I checked everything I could think of, never giving the bulbs a second thought. Finally took it to the dealer under warranty. The poked around forever until finally taking the CHMSL third brake light apart. They swapped the bulb back to incandescent and the problem was gone. For some reason, the LED was sending a braking signal back to the ECU and activating the ABS system. So weird.... 🤷‍♂️

 

I echo what the other folks said about the connector near the spare tire. Take it apart, check for corrosion or burn pins. If there is, clean them the best you can and either way coat it pretty good with some dielectric grease and if that wasn't the root cause the grease should help to keep the moisture out because it is a known issue. I rebuilt it from a salvage auction and I recently fought similar ghosts in my truck. I had hill start assist and advancetrac errors at the same time but I chased down all the connectors and issues that may have been the root cause. Mine ended up being that all systems had to be online and operational including the RCM which was disconnected but it taught me that many of the systems are not directly interconnected but do affect one another. In my pursuit of the problem I had come across one similar to yours and it turns out it was the the brake switch which is why I figured I could assist but if it isn't that, I have heard the back side of the ODBII connector being an issue and unfortunately the engine harness ( the one that contains the underhood fuse box) and if you tackled that one it runs around 800.00 online. Best advice is work the connector in the back which is most common then check for codes and although there may not be a silver bullet in the codes you should see enough evidence to find the commonality between the codes to get you there.

 

Sounds like a dealer trip to me.

 

Thank you everyone. Turns out common problem with water/corrosion getting into the main harness in the rear that goes to all the tail lights/blis modules. Only took 4 different dealer trips for them to actually replace the wiring harness. All problems are solved now. Guess I know which ford dealer I'm bringing my truck to when I need it serviced.

 

Any idea Where it is getting in?
would be nice to know so we can check ours to make sure we don't have the same issue 😊

 

Nice read and glad you got it fixed.

Greasing and sealing those connectors is on my "pre-delivery" checklist - stuff the dealer will do before I leave the lot with the new truck. And I'll pay for it if I need to.

Also included: Putting fog lights in Bambi mode, turning off double beep when looking door with fob, install tailgate damper (if not already) and give me an extra spark plug wire (as a spare)

I like this forum. It makes life easier.

 

Those were on my to-do list after getting the truck. For some reason, I didn't have the foresight and smarts to ask the dealer to do them, like you are! Actually, thinking about it again, I'm glad I did them myself, because when I dropped the spare to grease the connectors, I checked its tire pressure, and noticed it was only 45 PSI.

 

Thanks for posting this. I posted also with almost identical issues with mine, although they are constant (not related to stepping on brake). Dealer diagnosed front interface module but has halted that after it did not fix another truck with similar problems.