My 2019 F150 XLT 5.0 FX4 has been occasionally slow to start, sounding like a weak battery. The other day, it left my wife stranded. She left it, but a few hours later, it started right up. That evening, I measured the battery at 12.39V, which is apparently a bit low for an AGM battery. It cranked right up, reading somewhere between 14.5 and 15V while running. Given the age of the battery, I decided to go ahead an swap it out. So I pulled it, but without doing the memory saver trick. Within an hour, I had the new one hooked up, but now the truck seemed completely dead. Only, it's not completely dead. The gauges are lit up and the display shows the mileage of 40k. The key doesn't seem to do a thing. I pulled the parking brake and I could hear it operate and the parking brake message popped up on the dash. Headlights don't work. Brake lights don't work. The dome light doesn't work. The radio does work.

My usual OBD tools won't communicate. I have an OBDlink wifi that I use with my phone. It lights up, but won't communicate with the phone. I also have an older OBDlink MX (not MX+) that I use with a laptop. It also lights up, but will not connect to the laptop. I also have a Ford VCM II, but it seems my software is out of date. When I first got the truck, I used Forscan to disable auto start/stop using the OBDlink MX.

I checked for voltage in the main power distribution / fusebox behind the battery. There was full battery voltage at all of the lugs. I also checked fuses 4 (body control module), 16 (PCM), 76 (BCM2), and 41 (BCM voltage quality module feed).

Is there another major fuse that I'm missing? Anyone have any ideas? Is there another secret handshake cheat code? I haven't tried Up, Up, Down, Down, Left, Right, Left, Right, B, A.

Thanks for the help.
Erik

 

12.1 to 12.4 is fine.
Running voltage above 14. to 14.7 is proper.
You apparently have an issue in the starter circuit.
Ground, Power to the starter, or the starter has a fault.
Good luck.

 

I agree with Bluegrass. Perhaps your "slow to start" followed by a no start was not the battery in the first place. Check for voltage drop at the main power wire to the starter, and for voltage at the solenoid on the starter while attempting to crank. If both are good your starter has failed.

 

There is also a short ground cable that runs from the Bendix solenoid to the starter that some have had a problem with it corroding. I'd check that out as well.

 

My 2017 F150 Lariat did almost the same thing about 6 months ago. Mine however is a push button start. It did the same where it seemed dead and then finally started a couple times before it died in my driveway. lol Most of the electronics worked, etc but NADA on starting although I could hear a very faint click. Didn’t sound like a solenoid click at all. I tried everything I could think of and finally got tired of screwing around with it. I have an ESP on it so Ford sent a car hauler and took it to my local Ford dealer. They replaced the push button which did exactly nothing! lol Turns out it was the starter causing all the problems. They dropped in a new one and everything has been good.

 

I had a similar experience with my 2011 Silverado. Not so much with the electronics symptoms, but a failed starter is a killer. It was intermittent at first (wouldn't start), replaced the battery and it seemed to get better for a week or two. Then the intermittent starting recurred. Thinking it was the battery (again - because I have never had a failed starter), I tried to jump it. Melted the jumper cables. Direct short to ground through the starter. All those CCA's (like 650 amps!) Replaced the starter and its been going for 3 years now...

 

UPDATE: After tracing out numerous fuses and nothing making sense, I totally disconnected the battery.

Then I reconnected it.

It started right up.

What the heck? All's fine now.

 

It's going to keep biting you.
Here is the general path for starting.
.
Signal the event with a Button request.
That request goes to the Body Control Module.
The Circuit in the BCM activates the start relay through the Trans Neutral or Park position switch and powers the starter.
Also there is a starter time out circuit in play should the starter be powered to long.
It may be that powering down resets the circuit.
Likely fault in that line of communications.
Check for a possible fault DTC Code.
When powering down all codes will be lost, so a check needs to be done 'before power is removed', after a start failure.
Sorry to show it is not like old time starting circuits.
The vehicles are rolling computer systems and needs that kind of tech service to find faults.
Good luck.

 

In the mechanic world we refer to this as the KISS method. Keep It Simple Stupid. Lol