Never taken one apart but I’d guess the brake, once applied, is mechanically locked. When I disconnect my battery the doors don’t lock/unlock, my windows don’t wind down etc….why would something as important as the handbrake disengage? Dunno. Bloody good question though…

 

I think door locks etc are different. They have two fixed positions, i.e. open and closed and both are mechanically engaged/locked. The electric power switch just moves it from one position to the other and the position lock engages again. So, when power goes they stay where they are. Similar windows and sunroof are motors with gears and when power is removed the gear stays wherever it is. I think the brake is different as it applies a certain amount if pressure and holds it. There is no lock per se holding it as it has to have a predefined clamping force on the brakes.

 

So you're just remaining "immobile" thanks to the transmission being in Park...?!?!

siberian

 

I guess that is what it suggests. Next time my battery dies I guess I should see if I can roll the car some until the transmission in park prevents it…

 

Words fail me...

siberian

 

you may get it to roll 1/2 an inch. And by the way, the park brake won’t release when the battery dies. Quite apart from the logic of that I can tell you that from experience: my car is manual, I don’t have ‘park’ and it stays put battery or no.

 

That sounds more like it...

siberian

 

just reporting what warning comes up in dash when battery dies…it’s says parking brake not engaged, car my roll ..or something like that.

 

Understand. You get all sorts of warnings when the battery dies, the car has a slight hernia and really looses where it’s at. You learn to ignore them and focus on the real problem..no juice.

 

my original main point was that when car is parked the parking brake appears to require battery juice to operate and continue to hold…which may cause mysterious drain of batteries when car is parked for long periods.

 

yes, appreciate that. But no, best as I can see the actuator sets and releases the park brake but its not active other than when doing that. You can hear it in action, as I’m sure you’ve heard.

 

then why would it warn that it’s released and my roll when batterie dies? As i suggested before the electric parking brake is likely not a latching sensor but probably a solenoid type that is calibrated to a certain pressure. As rotors and pads wear it needs to adjust. The noise you hear is the piston retracting or setting. Who knows, but my guess it uses battery power to stay in place. Not much but something.

 

No idea sorry. All I know is I don’t recall mine doing that, it’s had a completely dead battery more than once and there’s a small slope on our garage floor so I’d have expected it to have rolled gently backwards.

From what I’ve seen in the work done on my car these last couple of months acceptable idle current draw is around 12-14 milliamperes. Is that enough to maintain clamping force enough to hold the car on a steep hill?

 

I can’t answer that. No idea what actuatos are used in real.
Another thought is that the e-brake can hold w/o power/battery (magnetic latching or simpler motor actuators etc) and the car just throws the scary message as its sensors don't work with a dead battery and it can’t tell anymore if the brake is released or engaged

 

In summary:

• When the battery is dead you don't / can't get any messages on the dash. The car is a brick. And the handbrake remains engaged.
• Frankly I can't see how the authorities would pass a car that released it's safety systems when the battery dies; imagine if it did that every time you changed the battery? It's illogical.