That must've been a scary experience for the child, but why did it happen? The snowy incline seems to be the reason.

This video captures a Tesla Model 3 parked on a snowy, slight incline. For no apparent reason, the car begins to slide backward on its own and smashes into a parked car. This occurred while a child was reportedly inside the car, so of course, the Model 3 owner (also the video uploader) was more than a bit concerned.

Was it operator error? Did the car malfunction? Turns out it's a bit of both, but more on that later.

Multiple additional videos were uploaded, including TeslaCam footage from several cameras, as well as footage from cameras mounted on the Model 3 owner's house. We've embedded them all below so that you can see the incident from a lot of different perspectives.

Porch 

Driveway

Front 

Back 

Left 

Right

We've watched the videos multiple times and what we don't see is the kid exiting the car, nor is it clear enough to see if the child is actually in the car while it's rolling. However, Andrew McKay, the video uploader and owner of this Model 3 says the child was inside when the Tesla rolled.

So, back to what happened. According to Andrew, it "turns out the front wheels don't have any mechanism to prevent them from rolling after the car enters a lower power state in park." Apparently this is mentioned in the manual, though not as directly stated as perhaps it should be. Other reports indicate the Model 3 has no mechanism in the front wheels to assist in holding the car in "park," regardless of the state of charge. However, the rear calipers have screw drives to prevent rolling and this Model 3 owner seems to think the fronts should too.

Per the Model 3 manual:

"Parking brake - Electrically actuated parking brake integrated into rear caliper."

Additionally, you can put your tesla into Park by pressing the park button and this automatically activates the parking brake. Additionally, you can activate the parking brake by hold the park button for three seconds, but this later procedure is more or less intended to be an emergency brake if the standard brakes ever fail to operate while in motion.

Any vehicle parked on a snowy incline may roll. The best methods to prevent this include equipping the vehicle with proper snow tires, avoiding parking on inclines, placing wheels chocks behind the tires and clearing the slick surface prior to parking.

You can read more about the incident in the description below and be sure to watch all of the videos and do let us know if you manage to see the child exiting the car.

Video description via Andrew McKay on YouTube:

We parked on a driveway in snowy conditions to charge at my dad's house. We've parked in worse conditions here before with our AWD Subaru. We felt safe with good tires on our Performance Model 3. No trouble getting up the hills to the house or up the driveway itself.

Posting this today because yesterday my Son asked “Dad was the Tesla sliding again?” as I opened his door for a goodbye high-five when leaving for a business trip (the car next to us had just pulled away and likely given him that illusion of moving backwards). It really hit me throughout overnight.

Turns out the front wheels don't have any mechanism to prevent them from rolling after the car enters a lower power state in park. You can see the tracks in the snow have tread instead of just lines from the front cameras. Totally counter-intuitive and not directly called out in the manual (to give some credit it is there if you read carefully).

I called the local Tesla service center and was told it would be as simple as adding the screw drives the rear calipers use and wiring them up. Why this isn't standard I don't know.

We love our car and purchased it for many reasons, the first being safety.

Elon, can we get a fix to make this car even safer?

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