Auto Start/Stop Failure
Thread Starter
Junior Member
Joined: Jul 2020
Posts: 6
Likes: 3
Auto Start/Stop Failure
I have a 2019 XLT Supercrew that I bought used a little over a year ago. Just over 44k miles on it. About 2 months ago, I noticed that it was occasionally (rarely) sluggish to start back up after the auto start/stop feature engaged. Didn't happen often but enough to get my attention. A short time later it failed to start so I figured it was time to replace the battery (last week) as the existing one was original to the truck. I did find it odd that I never had trouble starting it from cold but given the age I went ahead and bought a brand new battery. At the very first red light after leaving AutoZone, the auto stop killed the engine but it failed to start when I let off the brake. This has happened 3 other times since then. When it happens, I have to put the truck in park and restart it. Thankfully, it has (so far) started right up each time I do this.
This is a pretty dangerous situation if you are turning out in front of traffic, not to mention the reactions from people behind me when I don't go when the light turns green. For now, I am trying to remember to disable auto stop each time I get in the truck and I have an appointment next week to have the dealership look at it. The concern is that they won't be able to find anything since it is very intermittent. I may go several days with no issues and then have it happen twice on the same trip. No warning lights or anything so I doubt there is a code logged. The only warning that I get is a message like "hill assist not available" or "Service Trac not available" after the auto start fails. As soon as I restart the truck though, they are gone. Anyone have suggestions on what may be wrong?
This is a pretty dangerous situation if you are turning out in front of traffic, not to mention the reactions from people behind me when I don't go when the light turns green. For now, I am trying to remember to disable auto stop each time I get in the truck and I have an appointment next week to have the dealership look at it. The concern is that they won't be able to find anything since it is very intermittent. I may go several days with no issues and then have it happen twice on the same trip. No warning lights or anything so I doubt there is a code logged. The only warning that I get is a message like "hill assist not available" or "Service Trac not available" after the auto start fails. As soon as I restart the truck though, they are gone. Anyone have suggestions on what may be wrong?
5 Year Member
Joined: Jan 2011
Posts: 424
Likes: 325
From: San Francisco Bay Area
You changed the battery.....you may need to reset the Battery Monitoring System (BMS).
The stop/start quit on my friend's Lariat after a windshield change.
While we don't know if it's related to the windshield, we....
Checked the battery voltage - good
Unplugged the BMS (small plug at the battery)
Same trouble
Drove it - same trouble
Normalized everything (plugged in the BMS)
Went to lunch and it worked!!
Been working ever since!
might-a been that lunch! LOL)
Now we wonder if he has a weak or bad battery.....Hmmmm
The stop/start quit on my friend's Lariat after a windshield change.
While we don't know if it's related to the windshield, we....
Checked the battery voltage - good
Unplugged the BMS (small plug at the battery)
Same trouble
Drove it - same trouble
Normalized everything (plugged in the BMS)
Went to lunch and it worked!!
Been working ever since!
might-a been that lunch! LOL)
Now we wonder if he has a weak or bad battery.....Hmmmm
Senior Member
Joined: Mar 2021
Posts: 4,796
Likes: 2,395
Consider that the new battery was/may not be fully charged just because it is new off the shelf.
You started the motor, drove off then the Auto stop start tried to use the option when the battery is near to bottom of the allowable battery voltage for that function.
It amounts to two cranking starts with out enough recharge time.
If the mangement system had not been reset, the system uses the last battery history (and calculated age) that can still >under charge< the new battery in the short or long time use do to the last battery age still in the system. The system does this by design and intent of the control program.
Bottom line is replacement is not as simple as just repacing the battery any longer without attention to the details.
The vendor may not be able to do the reset or even know about it.
Reset does not take place by just removing battery power.
Good luck.
You started the motor, drove off then the Auto stop start tried to use the option when the battery is near to bottom of the allowable battery voltage for that function.
It amounts to two cranking starts with out enough recharge time.
If the mangement system had not been reset, the system uses the last battery history (and calculated age) that can still >under charge< the new battery in the short or long time use do to the last battery age still in the system. The system does this by design and intent of the control program.
Bottom line is replacement is not as simple as just repacing the battery any longer without attention to the details.
The vendor may not be able to do the reset or even know about it.
Reset does not take place by just removing battery power.
Good luck.
5 Year Member
Joined: Oct 2019
Posts: 2,122
Likes: 630
I have a 2019 XLT Supercrew that I bought used a little over a year ago. Just over 44k miles on it. About 2 months ago, I noticed that it was occasionally (rarely) sluggish to start back up after the auto start/stop feature engaged. Didn't happen often but enough to get my attention. A short time later it failed to start so I figured it was time to replace the battery (last week) as the existing one was original to the truck. I did find it odd that I never had trouble starting it from cold but given the age I went ahead and bought a brand new battery. At the very first red light after leaving AutoZone, the auto stop killed the engine but it failed to start when I let off the brake. This has happened 3 other times since then. When it happens, I have to put the truck in park and restart it. Thankfully, it has (so far) started right up each time I do this.
This is a pretty dangerous situation if you are turning out in front of traffic, not to mention the reactions from people behind me when I don't go when the light turns green. For now, I am trying to remember to disable auto stop each time I get in the truck and I have an appointment next week to have the dealership look at it. The concern is that they won't be able to find anything since it is very intermittent. I may go several days with no issues and then have it happen twice on the same trip. No warning lights or anything so I doubt there is a code logged. The only warning that I get is a message like "hill assist not available" or "Service Trac not available" after the auto start fails. As soon as I restart the truck though, they are gone. Anyone have suggestions on what may be wrong?
This is a pretty dangerous situation if you are turning out in front of traffic, not to mention the reactions from people behind me when I don't go when the light turns green. For now, I am trying to remember to disable auto stop each time I get in the truck and I have an appointment next week to have the dealership look at it. The concern is that they won't be able to find anything since it is very intermittent. I may go several days with no issues and then have it happen twice on the same trip. No warning lights or anything so I doubt there is a code logged. The only warning that I get is a message like "hill assist not available" or "Service Trac not available" after the auto start fails. As soon as I restart the truck though, they are gone. Anyone have suggestions on what may be wrong?
5 Year Member
Joined: Feb 2020
Posts: 4,118
Likes: 2,260
I also think you need to reset the BLM system. The great blue Gods at Ford made it simple. Find someone with Forscan that can do it OR go to the Dealer. Good luck, and I too would double check that it has a full charge.