If I got rear ended while stopped in "HOLD" is it the same as if I was stopped with my foot on the brake?
I don't think so. It uses secondary breaks, I don't think they are as strong as the main one's. Maybe someone here knows more about it.
I believe it engages the parking brake.
In hold mode the service brakes are engaged and your brake lights are on
From 2020.4 Manual for Model 3https://www.tesla.com/sites/default/files/model_3_owners_manual_north_am...
Pg 67 of Manual:
HOLD: Maximizes range and reduces brake wear by continuing to provide regenerative braking at speeds lower than with the Creep and Roll settings. When Model 3 stops, the brakes are automatically applied without you having to put your foot on the brake pedal. Whether stopped on a flat surface or a hill, Vehicle Hold keeps the brake applied, provided your foot remains off the accelerator and brake pedals. See Vehicle Hold on page 72.
When Model 3 is stopped, Vehicle Hold can continue to apply the brakes even after you remove your foot from the brake pedal. When driving on a hill or on a flat surface, brake as you normally would. After coming to a complete stop, simply press the brake pedal again (until the touchscreen displays the Vehicle Hold indicator light) to enable Vehicle Hold. You can then release the brake pedal and remain stopped, even on a hill.
This indicator displays on the touchscreen whenever Vehicle Hold is actively braking Model 3.
To disengage Vehicle Hold, press the accelerator pedal or press and release the brake pedal.
Note: Shifting into Neutral also disengages Vehicle Hold.
Note: After actively braking Model 3 for approximately ten minutes, Model 3 shifts into Park and Vehicle Hold cancels. Model 3 also shifts into Park if it detects that the driver has left the vehicle.
Note: When Stopping Mode is set to Hold (see Stopping Mode on page 66), Vehicle Hold engages automatically whenever Model 3 stops while in a driving gear. There is no need to press the brake to engage it.
If you hold the side of your foot against the side of the brake pedal, you can feel the brake pedal engage and hold while in hold mode.
The owner's manual states if Hold is not sufficient to bring the car to or keep stationary, press the brake pedal. Which implies Hold is doesn't have the same stopping/hold power as literally pushing the brake pedal.
My guess guess is Hold status engages parking brake (electrically actuated parking brake motors integrated into rear calipers push the calipers unto the disc.)
It seems like the consensus is that the brakes are applied - but somewhat unrelated, I just wanted to address pjwheeler83's comment that just because the brake lights are on, does not mean that the brakes are being applied. Each time you take your foot off the gas and regen braking kicks in, the brake lights go on.
I agree with @ stingray.don. I have felt the same movement/engagement of the brake pedal he describes as well.
Parking brake makes a totally different sound and takes too long to engage and disengage
Yeah, it is clearly not the parking brake. The car has hydraulic brake access so I expect it “holds” with that. What I’ve wondered is if the car also holds with the motor (e.g. for generating heat?) and I don’t have an answer to that.
@lessrandom, The motor is not the appropriate tool for implementing a hold function for a variety of reasons. One particular problem example would be that to implement hold with motor you would need a feedback loop to be able to vary motor energy based upon the force needed to hold position. Since desired speed is zero, there result would be small vehicle oscillations while holding position on an incline similar to a human doing the same with the go pedal. The car is clearly not doing that. Wasted energy, lesser holding capability, and reaction to external forces (wind, rear-ending, etc) are among other issues.
If you want to prove to yourself, you can implement hold on a very step incline. If the motor was used you would see noticable energy being used to hold position.
I hear a dim tapping sound from my accelerator pedal every time the M3 comes to a full stop under "Hold". Anyone else experience that?
Sorry, Rikki, I cannot trust anyone who spells "brake" the wrong way.
@ Wanderer, yep, that light tap or click is normal. For me it’s verification that it’s in hold. That and the fact I’m not moving. lol
So I did some tests....it does use power for motor hold until the brakes engage.
Brake* feel happy now? I wasn't asking you to trust me anyway
"The owner's manual states if Hold is not sufficient to bring the car to or keep stationary, press the brake pedal. Which implies Hold is doesn't have the same stopping/hold power as literally pushing the brake pedal. "
No, it means that if regen and one pedal driving would stop you just fine in five car lengths, but you need your car to stop in four car lengths, then you better use the brake pedal. It has nothing to do with strength but with distance, since it's not planning to come to a stop at a given spot.
Since the AC 3- phase motor is essentially a huge servo, having it hold zero speed is trivial. Yes, it requires a feedback loop but that's already the anyway. But that's terribly wasteful of energy (SWAPC) so it's only doing it for a fraction of a second before an actuator is enabled and moves to press the hydraulic brake. The hydraulic brake has sufficient braking power to stop and hold the car under virtually any condition. The parking brake would not be sufficient in all cases and would probably be illegal.
The marvelous thing here is that this is a feature that wasn't in the car when I bought it, but now it is. It's a testament to getting the design right the first time.
As a sidebar, the Oracle database engine has remained essentially unchanged since it was first written decades ago. It has not only survived but thrived essentially unchanged because it's creators got it nearly exactly right the first time. They keep bolting features onto it, including the ability to manage itself (rendering my OCP DBA essentially worthless, thanks, Uncle Larry).
Tesla is similar in that they've got it right the first time. They can add features that weren't there when you bought the car (hold mode) or improve features that were (rain sensing wipers) because the design had got it right. The first time. Refitting the cars with HW3 is an "oops, this really needs a bigger brain to run what's coming. Take the free hardware upgrade and wait for the software that exploits it.