I have a 2018 F150 Lariat, 3.5 EB, 46,000 miles. Today I took my truck to pick up my son and when I started the truck, the left blinker started to flash very quickly. I turned the left blinker on and it still operated slowly, but when turned off it went fast. Then my truck showed on both screens, "Parking Assist Fault See Owners Manual". I just had my windshield replaced last Wednesday which they had to recalibrate the lane keeping assist, so I was thinking it might be something to do with that. It drove fine for the 5 miles I had to go, turned it off, turned it back on and had the same error and blinking light, but drove home fine.

About a half hour later, my wife comes home and says all my lights are flashing. My headlights, tail lights and hazards are all flashing in a random pattern. I hit the unlock then lock button thinking it might be an alarm, and it stopped for about 30 seconds. It kept flashing and I can hear all the relays clicking. I tried to get my truck started, but when I hit the start/stop button, the screens turned on for a second then shut right back off. Since I couldn't do anything to stop it, I unhooked the negative cable off the battery. I tested my battery voltage and it was jumping between 12.45 and 12.5 volts. I left it off for about 30 min and came back out and hooked it up. It seemed okay, I tried to turn the ignition on and see if any codes came up, and it immediately started doing the same thing. My battery was testing 12.4 volts at this point.

So figuring it might be the battery, I went out and bought the same size and type, AGM, battery that was in the truck. I change out the battery, hooked up the new one, and same thing is going on. The new battery was showing 12.5 volts. I tried to get the ignition to stay on so I can use forscan to reset the BMS, but it kept turning off within 2 seconds. I tried to do the 5 high beam flashes and step on the brake 3 times as well, but couldn't get that to work. It wouldn't stay on long enough for forscan to reset codes or anything else. I was able to get it to start with hitting the start/stop button constantly until it started, but it died right away. I put it on my trickle charger for the night and will try to hook up the battery again in the morning.

I'm not sure what else it could be, unless some sensor or fuse went bad causing all these issues. Has anyone experienced this before? I have had gauges jumping around from a low battery on my jeep before which led me down this path. Sorry for the long post, but wanted to try to cover everything.

 

12.4 volts was normal on the old battery and was fine indicating there was no battery issue.
Don't do those things again just guessing.
Otherwise, there is nothing to point to a specific cause but have a dealer do the diagnostics since they may have saw this issue before.
Lighting and power for those circuits is usually done from a control module located behind the passenger side kick panel.
It may have been getting wet from a rain leak you can't handle, but let a dealer do the work and find the leak if that becomes the cause.
It may have to be replaced do to water corrosion.
The problem has to be proven before replacement.
The truck is a rolling computer with at least 30 modules on a Bus system.

Good luck.

 

All I did was change the battery, but my truck is still a brick. It won't stay on long enough to do anything to via forscan or even have the gauges come on to report a fault or error.

 

I would disconnect the new battery, get it fully charged, and try again.

 

So I charged the battery over night, it was just above 13.2V this morning and I installed it. The car started to function correctly, was able to turn the ignition on, do the BMS reset via forscan, completed that successfully. Started the truck and let it run for a little bit, everything seemed fine. I got ready for work and went to leave, then when I put it in gear, the active park assist fault came back. I was able to drive down the road about 1/4 mile and the truck shut off. A warning the transmission was not in park popped up with the truck off, but I put it in neutral to coast a little ways. I had to restart it 3 times to get it into a parking lot to turn around and get back home. I could start it after hitting the start/stop button a few times, but it would die within 30 seconds of running. It threw a wrench code on the way back at one point, but after restarting two other times after that, the wrench was gone on my dash. I haven't had a chance to try to pull codes because when I got back home, all the lights, inside and out, were flashing again. I ended up pulling the negative cable off again.

This is strange thing to happen and I cannot find anything through search of something like this happening to anyone else. It has to be something electrical, but not sure where to start since the computer is not showing any codes. Maybe something is grounding out or a wire was chewed through? I guess I can have it towed to Ford, but I was hoping someone might have had a similar issue in the past.

 

Issues appear to be electrical in nature. Engine, lights, warning, etc seem all unrelated to me (no common ground, comm network, etc). Would have guessed battery like you but - no joy.
First thought is to ensure battery connections (both + and -) are very clean and tight. Then have a look at the Battery to [body, frame and engine] connections to be sure they are OK.
A gross parasitic draw maybe? ??????

 

I checked at lunch time again and my newly bought battery was down to 12.4V after trying to drive it this morning for the short amount of time the truck would stay on. I disconnected it right when I got home and didn't check the voltage until lunchtime. It seems like there is a large power draw somewhere, just not sure where yet. I have the battery on the charger again, hopefully it will start and move enough to get it into my garage after work so I can have better lighting to work on it into the night tonight. The battery cables are all tight and had no corrosion on the old battery or terminals. I will clean them with a wire brush tonight to make sure they are clean and have good contact.

I also checked continuity between the unconnected negative cable and the engine block, as well as the frame, both had continuity. But there could be other wires that are grounding out a power wire or a bad sensor causing the battery drain. The first fault was the active park assist fault, so I'm going to check all the sensors and wires visually to start. That also could have been shut down by the BMS for low battery voltage though prior to everything else being shut down. I'm going to keep searching.

 

You have a right to do whatever you want but you're wasting your time with no knowledge of what you're doing.
If the truck has an AGM battery, 12.4 volts is the >>normal state of charge<< and indicates there is no large discharge present and battery is being charged by the Alternator, when the engine is running.
I told you there is a module that controls all the timing and lighting on the truck under electronic control.
It's the common point for all lighting control and a place to begin with >>>diagnostics.
You cannot do a fix with the way you're going about it.
This is in effect, the help I have tried to offer and not being hard-nosed about it but trying to tell you you cannot work this way, on a complex system.
Good luck.

 

Has the alternator gone bad (not suggesting replacement, only testing to determine)? A scan with FORSCAN for all DTCs might provide insight into the issue. Be aware a majority of the DTCs will be electronic related and are only symptoms not the root cause.

 

Sounds like a ground issue check for a loose ground. The one behind the passenger kick panel is notorious for behind loose

Also the trucks alternator needs to be tested off the truck I think to get a accurate reading. I could be wrong tho.
I know there's a sensor on the battery that tells the computer what volts to charge the battery. So it will fluctuate.

My truck kept throwing a charging warning and when you test the truck at autoparts stores it shows a bad voltage regulator. But the alternator tested fine off the truck. Mine ended up being a damaged wire