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How do I stop this unintended acceleration?

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I was visiting the Arby's drive-thru today in Pryor, Oklahoma. It's located next to hwy 69, which has a 35 mph speed limit. I had either the autopilot (non-beta) or cruise control on before I pulled in. I stopped to order, then I stopped and had to wait a bit on my food. I had the car in park.

After I got my food, I put my food on the brake, hit the "drive" lever a couple of times (a habit, because it sometimes misses it the first try).

I am absolutely certain I didn't press the accelerator more than just a tap. There was a car a few feet in front of me waiting on food. My car took off in a moderately fast acceleration (which seemed really really fast at the time) toward the parked car. I heard the three beeps I get whenever I unsuccessfully try to engage autopilot.

I slammed on the brakes right away, but the car was going fast enough that the tires skidded when I stopped. (Nice acceleration, even in chill mode.) I'm pretty sure the Arby's employees and the people in the car I almost rear-ended were impressed with my superb driving, but being the humble soul I am, I did not wait around for compliments. To add insult to injury, Arby's was out of turkey and I had to get beef!

At this drive through, my car always thinks there is a 35 mph speed limit, even inside the drive through. This is not the first time its happened at this drive-thru. I've seen it at least a dozen times. This is the first time I've almost rammed somebody, however.

I have tried to duplicate it, but haven't been able to consistently. Either I haven't hit on the right combination of commands, or it's an intermittent occurrence with the car. I would like to re-iterate that I am definitely not hitting the accelerator too hard.

I am not interested in demanding a recall, contacting the NHTSA, etc., as it would be a waste of time. I'd like to see Tesla fix the bug, but trying to get that done would also be a waste of time.

I would like to know if anybody else knows what's causing this. How can I prevent it? It seems like it must be a software problem, in which case there must be a specific situation that causes this to happen. Maybe someone else has experienced this and analyzed it? My car is a 2020 Model Y, the VIN number ends in 001271.
 
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It may have been unintended, but it was caused completely by you. Kill the habit of double clicking the lever, as you caused this reaction from the car yourself:

=============================================
(directly from the manual)

Operating Autosteer​

Before you can operate Autosteer, you must enable it by touching Controls > Autopilot > Autosteer (Beta).
Icon of a gray steering wheel.
To indicate that Autosteer is available (but not actively steering Model Y), the top corner of the touchscreen displays a gray Autosteer icon next to the driving gear.
To initiate Autosteer, move the drive stalk fully down twice in quick succession.
an arrow pointing at the door handle

When a vehicle is detected ahead of you, you can initiate Autosteer at any speed, even when stationary, provided Model Y is at least 5 feet (150 cm) behind the detected vehicle.

==========================================

So, you double clicked the stalk, initiating autosteer. Because there was a car ahead of you, you were able to initiate autosteer "even stationary". You tapped on the accelerator pedal to move, and the car moved, with autosteer on. All completely as designed.
 
Thanks! I'll look into that.
Regarding the double press, from a stop, if I press the brakes and then the drive lever without a long enough pause in between, it won't do anything. Then I have to hit the drive lever again. That's where the double-press habit comes from. I hope I'm trainable!
 
Thanks! I'll look into that.
Regarding the double press, from a stop, if I press the brakes and then the drive lever without a long enough pause in between, it won't do anything. Then I have to hit the drive lever again. That's where the double-press habit comes from. I hope I'm trainable!
True. It takes a couple of seconds to ”wake up” before it will register the drive stalk push down. You can watch the screen for all the red icons on the left column to disappear as the car wakes up.
 
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Thanks! I'll look into that.
Regarding the double press, from a stop, if I press the brakes and then the drive lever without a long enough pause in between, it won't do anything. Then I have to hit the drive lever again. That's where the double-press habit comes from. I hope I'm trainable!
If you hold the stalk depressed, it puts it into N. It's simple. Foot on brake - pull down on the stalk once. Now you're in D.

As others have said, pull it down twice puts it into traffic aware cruise control (D the first time, CC the second time) -- which is likely why it took off.
 
You can also change the cruise control/autopilot speed setting from speed limit to current speed. This will prevent your Tesla from accelerating to what it thinks is current speed limit.

Per the manual:
You can choose whether Traffic-Aware Cruise Control engages at the currently detected speed limit or your current driving speed. Touch Controls > Autopilot > Set Speed and choose either Speed Limit or Current Speed.
 
When a vehicle is detected ahead of you, you can initiate Autosteer at any speed, even when stationary, provided Model Y is at least 5 feet (150 cm) behind the detected vehicle.

==========================================

So, you double clicked the stalk, initiating autosteer. Because there was a car ahead of you, you were able to initiate autosteer "even stationary". You tapped on the accelerator pedal to move, and the car moved, with autosteer on. All completely as designed.

I understand it was initiated by my double click and I'll handle it.

However, there are some weirdities.
1. My car should not have kept going into the other car (and I believe it would have).
2. I have initiated autosteer on interstates a few times in similar situations (stop-and-go traffic), and my car didn't accelerate like that. It always went up to the next car, accelerating slowly, and stopped gently.
3. There are not proper lanes in that drive-thru. Autosteer was not active, and beeped three times to confirm this before I hit the brakes.
4. This has happened to me several times at this location, and each time before this there was no car ahead of me in the drive-thru.
 
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You can also change the cruise control/autopilot speed setting from speed limit to current speed. This will prevent your Tesla from accelerating to what it thinks is current speed limit.

Per the manual:
You can choose whether Traffic-Aware Cruise Control engages at the currently detected speed limit or your current driving speed. Touch Controls > Autopilot > Set Speed and choose either Speed Limit or Current Speed.
Thanks, it was already set on current speed.
 
Think of it this way so you are less likely having to press the lever multiple times.

When you press the brake, the car goes through all its system checks to make sure everything is in working order before it allows you to go into DRIVE mode. This is illustrated by those icons lighting up on the left side of the screen. Once they all go away, that means it has finished its system check. This is when you should press the the lever.

If a problem is detected, you'll not be able to enter DRIVE. It's a built in safety check.

We often press the lever right after pressing the brake, so the 1st press usually is ignored and sometimes we don't understand why it has to take 2 or more presses to get DRIVE to engage.

What I tend to do is not to press it too quickly between presses. I usually give 1 or 2 seconds pause between presses.
The other option is to keep holding on the brake until you can enter DRIVE mode (by visually look at the screen). This should turn off autopilot if you accidentally engaged it.
Another method is to step on the brake first before putting on your seatbelt. Once you have your seatbelt on, you can then pull the lever to engage DRIVE mode.
 
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I understand it was initiated by my double click and I'll handle it.

However, there are some weirdities.
1. My car should not have kept going into the other car (and I believe it would have).
2. I have initiated autosteer on interstates a few times in similar situations (stop-and-go traffic), and my car didn't accelerate like that. It always went up to the next car, accelerating slowly, and stopped gently.
3. There are not proper lanes in that drive-thru. Autosteer was not active, and beeped three times to confirm this before I hit the brakes.
4. This has happened to me several times at this location, and each time before this there was no car ahead of me in the drive-thru.

Perhaps you were in traffic aware cruise control instead of autosteer. We dont know if the car read traffic aware cruise control or autopilot. both can be set from a stop. Im not going to post large swaths of the manual for traffic aware cruise control since it would likely be seen as piling on or something, but maybe something in there under that feature answers your questions.

One thing we do know, however, is this was not "the car took off on its own".
 
I’ve found that when I put the car in Park and back into Drive during the same drive without leaving the car (such as dropping someone off at a curb), it does not do the icons on the left and gets right back into Drive when I click the stalk down. I don’t think the OP left the car in the drive thru, so it most likely activated TACC on the second click.
 
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Don’t put the car in park. Have it in hood mode if you don’t want your foot on the brake, or keep your foot on the brake.

Also, just go inside ;)
I think this is the best solution for OP. There's no reason to engage park in the drive through. Just pull up, car holds, hit the accelerator when you want to pull away. There's no need to get the right stalk involved at all.