Driving along, warning that vehicle hold unavailable, found brakes werent working. Pulled over and thankfully parking brake works fine. From there even pressing brake pedal couldn't change "gear" saying I need to hold the brake pedal. F'in scary as I had my baby in the back. Thank f regen also worked by the lights when the problem occurred. Tow truck on way...
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M3P brakes have stopped working
- Thread starter odyssey96
- Start date
ACarneiro
Active Member
Holy cow! Sound like “brake by wire” was faulty?
Should it happen to anyone else, pressing the parking brake switch will gradually apply the parking brake and can be used for emergency braking.
Should it happen to anyone else, pressing the parking brake switch will gradually apply the parking brake and can be used for emergency braking.
Jason71
Well-Known Member
Really. I didn't know that. Does that work at any speed not just the 5mph where you can officially use it?
ACarneiro
Active Member
Works at any speed. I suspect it’ll be a fairly assertive brake but won’t just “drop the anchor” and break things.
Will update as soon as root cause identified currently at Tesla service center. Funnily enough I was checking franticallyfor software updates and as soon as it hits the service centre low and behold on the app it says it's downloading 2020.8.3. I was sure not to start the upgrade in case they were in the middle of some diagnostics lol. In my head I was playing pranks by opening and closing the charge cover 
Model 3 has a direct mechanical link between the brake pedal and the tandem master cylinder via Bosch iBooster. This is discussed in the leaked theory of operation document:
MrBadger
Badger out
ACarneiro
Active Member
ABS and ESP can reduce the braking force but not disable the brakes completely, so the only thing I can think of is a total loss of pressure in the hydraulic system. But, of course, that's not something the car can recover from by itself. Last time a report of brakes "just not working" popped up on the forum, I think the consensus was that the poster first put the car in neutral (instead of disabling autopilot) and then pressed the accelerator pedal instead of the brakes. That's one hell of a coincidence but not impossible. Curious what Tesla tells OP.
The brake pedal was locked in its non-pressed position. Like I think if you tried to brake a ICE car without the engine turned on, you'd have to slam your foot down. But in this case brakes didnt seem to work. Only by regen braking and driving real slowly came to a stop.
Here's the immediate previous history:
All working for 3 or so days. Car wash. Drive to CCS charger down road and drive back successfully.
This day - unlock car via mobile app and get in car and enter pin to drive. While in park, tell wife to connect her phone via BT (thought we could connect both phones simueltaneously using BT, didn't realise it disconnected mine). Brake locked in 'upper' position, when pressing it hard and trying to put car into drive, kept saying Press brake to change gear or whatever. After several times of trying reverse/drive, finally goes into drive. Thought it was a bug. Went forward slightly to then perform a reverse (I live at the end of a closed road, car facing towards end). Found I couldnt brake, 'Vehicle hold function not working' on screen. Only because of (very slow at that time) regen stopped. Crapped pants, came close to curb. Got wife/toddler out of car, locked it by walking away. Disconnected wifes phone, unlocked via app and got back in, all fine. Thought this is a serious serious bug and ill report.
Then got down the road and the 'Vehicle hold not working, use brakes when stopped' appeared again. Brake pedal locked in the upper position again. Hazards on, accelerate very slowly and try brake, cant press the pedal down. Turn into side road, come to stop, parking brake, roadside assistance.
When I posted at first, was on mobile and i was shaking slightly from how scary i found the situation given my baby in the back.
Here is the error above. I didnt mention the initial mobile issue as I can't see how it was a bug if the problem then occurred the second time around, just a freak coincidence imo.[/QUOTE]
Attachments
Got car back and all seems good. In case anyone wanted to know:
Rustybkts
Member
Are they saying that a poor ground connection completely negates any brakes at all, even backup hydraulic only braking?
That's kind of a "screw off" repair. The errors above are consistent with the booster motor failing to move the pedal, but the root cause - the pedal being stuck hard in unpressed position - is rather odd. I wonder if it was something mechanical and transitory - like a small pebble or a poorly tailored floor mat getting stuck in the way of the pedal arm. If ibooster failed and no electromechanical boost was available, the car should have engaged a backup system that uses the pump that normally applies the brakes for traction control to hydraulically boost the pressure you were putting on the pedal. Again, from the theory of operation doc:
Even if this secondary hydraulic booster system failed too, you would still be able to brake. The pedal would be very stiff but still possible to press down and the force would still be transferred to the TMC by a push-through rod in the ibooster (that's the bit I quoted in my previous comment). This makes me think this wasn't an electronic issue but rather a mechanical one, with something physically preventing pedal travel. Either way, this must have been very scary, glad you were able to slow the car down and that everyone is OK.
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That's a very inadequate explanation for such a serious problem. Surely they looked into the failure in greater detail ?
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