Obtain your VIN and check to see if your vehicle was one covered by the brake light switch recall. If it was, and not repaired yet, that would be my guess as to the cause…

 

The car does not appear to be covered by the brake switch recall.

 

Check out this link to see if any of this seems familiar…

Brake light switch: symptoms, problems, testing, replacement

What is a brake light switch in a car, problems, symptoms of a failed brake light switch, replacement

www.samarins.com

 

This could be the effect of a failing battery. Many of the 2019 batteries are failing now, per the many posts about them. Mine showed the end of its life was near rather suddenly with a similar effect, but on a manual start. (I have auto s/s disabled.) It did start OK a few more times after that, but probably the battery voltage was dropping low enough on the initial load of the start attempt to reset related electronics.

 

yes, I could see the voltage dropping pretty low under load... especially since the air conditioning was working overtime in the daytime heat.

 

Feline Freddie posted at the same time as I did, and that's certainly another possibility. However, if your problem turns out to be elsewhere, or does not happen again - given the battery issues posted here, keeping an eye out for any similar effects, or having the battery load tested, is a good precaution.

 

Yeah the battery is definitely on its way out. I’ve been thinking about upgrading to a 24F AGM (will require a new tray and strap, but it should fit). The stock battery has been garbage from the beginning.

 

AS/S is not suppose operate (ie, stop the engine) if the battery is weak. That is one of the many "Non-operational" conditions listed on page 342 of your owner's manual.

 

According to the OP's profile, he has 54k miles on his 2019 so he is out of factory warranty on the battery.

 

@Cddelta That happened to me too Took it back to the dealer & they replaced the starter and i also got a new battery! Just got it back today Another problem I had was the map freezing up—

 

@MJD glad you got your car sorted. I replaced my battery and have not had any further issues.

 

At a stop light, my engine shut down as expected. When the light turned green, and I lifted my foot off the brake, the engine failed to restart.

Same for me and my 2021. It is at the dealer. After an hour they said they were keeping it to give it some stress tests and look at the Auto Stop/Start Battery. Gave me a loaner and sent me home. Service writer commented that he has been seeing quite a few of these lately. Maybe a software update glitch, as I just had my 12K service.

 

I have a 2021 and mine just did this at a light this morning too! Stopped at light, turned off as it should and then dash lit up and wouldn't auto start. Started up fine after I put it in park and restarted it with the push button. Did they ever tell you what the issue was?

Just curious if mine may just be the battery (since their stock batteries have always been trash). I'll pay money for a better battery rather than see if mine is still under warranty and have them replace it with another trash battery.

 

New battery resolved the issue

 

AS/S is not suppose to turn the engine off if the battery is weak:

 

AS/S is not suppose to turn the engine off if the battery is weak:

If the battery has a good state when AS/S activates, but quickly falls off as the load from the accessories is placed on it, it could fool the PCM into letting AS/S being initially activated. Then the battery drop probably cancels AS/S after it's already activated. With the alternator keeping target voltages in the acceptable range, it is totally possible.

Normally it will restart before the voltage drops below a certain point, but if it drops rapidly enough...

 

@ForesterBill A battery in poor health can show proper voltage, but when you put a load on troubled battery, you won’t get enough power to start. I see this all the time at work where a battery is fine when properly charged, but won’t hold the charge with any load.

 

I am having a problem with my Forester's auto stop start system and would like to know if anyone has had, and solved, a similar problem. I have driven with the auto stop start system for several years and have had no problems until the last four months or so. Occasionally, about once a week or fortnight, beginning about four months ago, when stopped at traffic lights, with the auto stop activated, when the traffic light turns green and I put my foot on the accelerator, the engine does not restart, but shuts down the engine entirely, stalls the car, and the car must be put back in park and restarted with the start button. At a busy intersection this is dangerous and frustrating. I have returned the car to the dealer/service centre to examine and they have said there is nothing wrong. Any thoughts???

 

I just left Subaru with this same issue. It has happened to me three times in the last two weeks. They couldn’t replicate it on test drive, the computer codes checked out, and battery test passed. Same thing- at a red light with my foot on the brake, I take foot off when light is green and the engine doesn’t kick on. Many warnings pop up on the dash, a loud beeping, and says restart car for my safety. I put in park and restart. Did you ever get any more information? I have my car back and am prepared to record this, but obviously this is dangerous.

 

Perhaps it would help to make a video of the behavior to show the dealer, since they haven't been able to replicate the problem.

I'm a little confused by the behavior, as you describe it. The engine should restart when you remove your foot from the brake. You're saying it doesn't restart when you give it gas. But when you give it gas it shuts the engine down, or stalls it. So it IS restarting, but then stalling after you give it gas?

I haven't had an problems like yours, but with some clarification, maybe others can help.

 

It is always very stressful when it happens as I am in a line of traffic with someone honking their horn and trying not to rear end me, however I think you are right to ask for clarification. I think it stops when I take my foot off the brake, in the split second before I put my foot on the accelerator.

 

Found this on a google search as this just started happening to my 2019 last week! So stressful at a light with lots of people behind me. My 72k service is coming up so I’m going to ask them to look at it. Annoying as it’s worked great for 3 years.

 

Two times recently, while sitting at a stoplight, the engine will automatically cut off as it should to save gas, but when I step on the gas pedal to go again, the engine gives an attempt to start, but cuts off. I am able to turn the key and restart the motor and no warning lights are lit, but it worries me that something is amiss. Car has about 66,000 miles on it.

 

It's most likely your battery getting weak or a low charge level. The factory Subaru battery does not have the longest lifespan. There are a couple of things you could do. You could get a float charger and keep your battery topped up when you are parked at home or you could consider buying a new battery.
Technically the auto stop start system should not engage if the battery level is too low to restart the car, but somehow still runs into this problem.

 

@OuchDamn The Forester batteries seem to fail rather suddenly and a bit erratically, going by my own battery and many posts about them here. I question the ability of auto stop/start to always judge a marginal condition of the battery and the ability to restart correctly.

 

Love my "Auto Start / Stop" eliminator. Also, she has a battery maintainer on her if gonna be parked more than just overnight. No issues.

 

Battery is getting weak.

I've saved almost 11 hours of engine run time with the auto stop so far, it's pretty great.

 

This is the first post I've seen of a marginal battery causing something like this, and there have been plenty of posts about failing batteries over the years. Why would turning the key still start the engine if the battery is kaput?

 

Maybe the A-S/S refuses to work if it detects just a near dead battery? Using the key then "forces" the issue. An "A-S/S eliminator" eliminates the concern ... as does simply deactivating it manually at each start.

 

Please stay on topic and help not turn this into yet another I-Hate-Autostart thread.

@SerenityNow - I suppose a weak battery could be the problem, but as I said, the set of symptoms you're experiencing haven't been noted previously in the forum, so you would be the first.

You can get your battery tested at pretty much any parts store. If a new battery fixes the problem, do let us know!

I thought my 2019's battery would be on its way out by now, but it just keeps plugging along (helps that I don't live in a hot climate).

 

@boureesub

('19+) - 2020 - Extended battery life - turn off...

Could those of us that habitually turn off our Auto Stop Start expect to get a much longer life span from their battery? I would imagine a A.S.S. system in constant use would require a battery of much higher spec to handle all those extra starts. So, would it be fair to figure that NOT...

www.subaruforester.org

('19+) - 2021 - Stop/Start function and Battery...

I have 5 month old 2021 Forester and have been reading about the low capacity/rating of its battery. I hate the stop/start function and usually turn it off upon starting the vehicle. My question is: does this feature cause the battery to degrade faster over time? Thanks.

www.subaruforester.org