Dangerous flaw in the parking brake logic? [issue resolved after owner testing]

[Gauss Guzzler]

Last night I had finished positioning the car on a steep hill and it was "holding" in the usual ABS-driven mode flawlessly and seamlessly as usual - until I pressed the "park" button. The ABS *instantly* released, sending the car into a backward freefall for about 2-3 feet down the hill until the slow jackscrew had engaged far enough to jolt it to a violent halt!

Yeah, I know. You're old, you're cranky, you're gonna lecture me about using the brake pedal. Whatever boomer. The fact is that someone made a mistake in the parking software by commanding it to immediately release hold mode (for no reason?) before even starting to apply the parking brake rather than simply waiting until after the jackscrew is done. Not only is this the correct way to do it from a safety standpoint, but by taking advantage of the hydraulically pre-clamped caliper the jackscrew could operate faster with less noise and wear by simply locking the pads in place rather than actually moving them.

What if a passenger had opened their door while I was "holding" on a hill? That would probably trigger the same event, right? What if some friends had approached the car to greet us and a passenger opened their door before I put it in park?

Surely I can imagine a car parked behind me on the hill, friend comes up to my trunk with luggage and I realize that I can't open the trunk until I put it in park...

 

[XPsionic]

hmm i don't recall the car ever rolling when i park on hills. I drive using hold mode. Are you on creep or roll mode?

 

[TomT]

I park on a steep hill all the time. I've never experienced that.

 

[Gauss Guzzler]

Update: I just did some experimentation and concluded that the issue was mostly my fault (apologies to any boomers). I say "mostly" because even though the issue was entirely my fault, it could certainly be made better in software.

So it turns out I wasn't quite in hold, I was applying just enough pressure to the gauss pedal to keep the car near 0mph without activating hold. So really the flaw is that it doesn't automatically activate hold (with the ABS pump) before engaging the parking brake but it does immediately cut the motor power.

 

[Park2670]

I have experienced what you did, and you are right in your update. Its if you have your foot on the go pedal and then put it into park. Its definitely jarring and scary.

 

[bo3bdar]

Update: I just did some experimentation and concluded that the issue was mostly my fault (apologies to any boomers). I say "mostly" because even though the issue was entirely my fault, it could certainly be made better in software.

So it turns out I wasn't quite in hold, I was applying just enough pressure to the gauss pedal to keep the car near 0mph without activating hold. So really the flaw is that it doesn't automatically activate hold (with the ABS pump) before engaging the parking brake but it does immediately cut the motor power.

Thanks for the update and also for recognizing that you weren't doing this well. It's not about being a boomer/old/young, it's about driving properly. In your example of someone wanting to put luggage in the car- even if it wasn't an EV, would you do that without being in Park? An automatic transmission ICE car would be just as risky. If you used that move during a driving test, you'd be failed immediately, regardless of car. When you are parking, foot on the brake. The cars are safe and pretty smart, but there is no substitute for good habits.

That jackscrew mechanism doesn't seem all that great, another reason to be sure about car state and brakes when getting out. I wouldn't recommend relying on stuff like Tesla's auto-park when you open the door, you are just asking for trouble.

 

[Gauss Guzzler]

The jackscrew is fine and my tests today proved that the car always waits until the jackscrews are done before releasing the hydraulic hold. I tested every combination of uphill/downhill/drive/reverse with/without brake pedal application on a very steep hill and it was flawless.

It's just that odd case of going straight from Drive/Reverse into Park without ever entering Hold mode that's the problem.

Perhaps what's happening is that I'm actually activating the emergency brake which cuts the motor power, applies the parking brake, and then automatically shifts into Park once the car has come to a stop.

I can understand why they wouldn't want the emergency brake to trigger Hold mode - it would just lock up all 4 wheels! But they could add some simple logic to apply Hold mode if the E-brake is pressed below 1mph.
Or I could learn to drive better.

 

[bo3bdar]

The jackscrew is fine and my tests today proved that the car always waits until the jackscrews are done before releasing the hydraulic hold. I tested every combination of uphill/downhill/drive/reverse with/without brake pedal application on a very steep hill and it was flawless.

It's just that odd case of going straight from Drive/Reverse into Park without ever entering Hold mode that's the problem.

Perhaps what's happening is that I'm actually activating the emergency brake which cuts the motor power, applies the parking brake, and then automatically shifts into Park once the car has come to a stop.

I can understand why they wouldn't want the emergency brake to trigger Hold mode - it would just lock up all 4 wheels! But they could add some simple logic to apply Hold mode if the E-brake is pressed below 1mph.
Or I could learn to drive better.

Thanks for those interesting test cases, worth knowing those other scenarios are fine. Definitely agree that this could be improved by Tesla, more like a software glitch or oversight for this scenario. Seems like it would be logical to have the software apply the brakes also when putting into park. Can't think of any time you would not want that. Sure wish we could provide feedback/bug reports to Tesla that would be seen, this would be worth fixing.

I'm not a fan of emergency systems requiring power, electronics, or working computers. For an emergency brake, I really just want a dumb cable that I can yank hard. I'd much rather have just a regular old parking brake as the failsafe than this jackscrew mechanism. It's like some of the emergency situations we read about here- can we always be sure there will be a working computer to respond to that button? The three second delay to activate by button push- a delay during an emergency situation just is not good. We can't foresee the scenarios, I'd much rather have something bulletproof.