2018 F150 40K miles, the Auto Stop/start has stopped working, The switch says it is on (not lit) however the Icon on the Display shows it not active (Circle A with a slash through it)

Any idea why it stopped working?

 

How well is the battery charged? I wouldn't be surprised if the OEM battery was near the end of it's life, even though it's a 2018.

 

X2 on battery. Can you go into display, I've heard some will tell you why it is turned off, ie charging etc.

 

The battery is the most likely culprit, as pointed out by others.
You can have your battery tested to confirm it's health.
Or, if you have a charger...charge it up and see auto start/stop begins working again.

 

Or take it on a highway drive of 30 minutes or more to charge the battery. Short trips don’t allow the battery to get fully charged. Daily short trips will never allow it to reach a full charge.

 

Actually the way the BMS is programmed the opposite is true. You can watch this in forscan live as it happens. These trucks run the alternator on coast coast decel mostly. They float charge at cruise and that's why you normally see 12.8v to 13.2v at cruise. The OP is due for a battery at that mileage and the BMS has probably canceled the start stop either due to days in use or charge rate inconsistencies.

 

Some of us would pay good money to have the stupid thing magically not work. I've noticed my battery is getting weak when I start it on cold mornings but the stupid auto start is still working.

 

Good to know.

How about the short trip aspect though? I know many guys who, on a regular basis, don’t drive much distance.

 

Ford has it in the algorithm to rapid charge. After the first 10 seconds of starting you often will see a rapid 100% and near 14.8v. The addition of the AGM battery really improves the charge and discharge rates.

 

I have a test plug in the 4 pin trailer socket to keep the auto start inactive.
A test monitor in one 12 volts dash port to watch the charge rates and when they occur.
The system checks the temperature and voltage before and after as the engine bay heats up.
I notice in this cold weather the charge does not happen until some time later after cold starting. A normal timing function to reduce the drag on a cold engine and Battery and Alternator.
In these temperatures it also depends if the head lights are on, if the heater motor is being used and how often you stop and restart the motor.
Seems there are a lot of dynamics to consider before concluding anything about system operation and/or battery failure.
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My dash switch makes no difference whether on or off by manual operation because it is over ridden from another input. Not only does it signal the PCM but a separate power feeds the lamp, so it makes no difference if on or off if the function is over ridden from another source. You can't override the lamp in the switch It will do as directed either from the system or manual operation.
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My truck is a 2018 5L at near 40k miles. Battery is original AGM type.
Started every day, run short distances, restarted several times. I expect some extra charging time from this kind of use.
The Monitor is a simple LED design that can monitor the Alternator and the Battery as separate functions. It does this from a 'single connection' in any dash power port via sensing the PCM addressing the Alternator when the pulses appear 'riding' on the DC level and at what frequency they occur.
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Over the long term if it's observed the charge is being applied for excessive amounts of time, the engine cranking get slower, it's likely time the battery is nearing practical end of usage and should be replaced.
One has to be observant and use common sense..

 

Consider yourself lucky, I had to buy a $50 module to get the same thing you have for free.

 

Bluegrass 7,
My truck doesn't have that many miles (17,000), but it is almost 3 years old. It got the battery changed for Free. It started on the Monday the 8th when they installed a new door handle assy (which the body shop forgot to paint) because the sensors had quit working. That didn't cure the problem, so then they ordered installed a new BCM, had to reprogram it twice, during all this they had charged the original battery. Had trouble with slow starting and still BCM still having problems.was going to stage it for me to pick it up and no start at all. They put in a new battery, cured all problems. since all this took about a week longer than promised even though I was driving a band new loaner, an Edge Titanium. We bought it this past Saturday, let me keep and drive our old Edge trade-in. So that is how I got a new battery along with all the other parts.
I was happy in one way because I had something to drive and they didn't give it back half way fixed and stayed with it until it was completely repaired.
I have had nothing but Great service for the past 20 years from my dealer. I have no problem telling people to go to them.
TJ

 

For some reason when I tried a 4 pin test plug in my trailer socket it doesn't stop auto ss from working. 2020 F150 XLT. 5.0 L. Any ideas?

 

FORScan will stop it permanently. I don't mind Ford striving for better mileage ratings with the Fed, but not at the expense of my starter.

 

Considering they test the starters during development (and again any time a change is made) for a very large number of starts that should reach 100k (I don't recall the number but Ford has a spec on it), your starter will likely last a LONG time even if you sit in traffic quite a bit.
The starter on a truck with Auto start/stop enabled is built to last as long as a starter on a truck that never had auto start/stop on it. By disabling Auto start/stop, you are extending the life of a product that was already designed to have a long life. I'm not saying it's a bad thing, I'm just saying that these starters are stout, and the belief that auto start/stop means you will replace the starter more often is not based on fact, but a 'gut impulse' of people who don't understand the amount of testing new component designs have to go through.