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Power braking assist reduced

sho12345678

Member
Jun 27, 2019
37
14
Midlands
Hi all,

I've never had a problem with my M3SR+ in 16 months, then this morning the brake pedal barely worked with the error as per the title.

I drove for about 1 minute before turning back. Luckily I had a bit of regen breaking to help come to a stop, but to come to a complete stop required forcing my foot down hard on the brake pedal to the maximum limit it would go. Stopping at a junction was almost impossible.

The feeling and sound of applying the break was similar to when you are juddering and pumping the break when skidding on snow.

A call to my local service station advised me to call the roadside assistance option. They advised a power off cycle, which I tried when I returned from work only to find everything working perfectly again!

What on earth happened here! There was snow over the weekend but it's all melted and the had been no ice.
 
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AndrewGR

Member
Oct 18, 2019
390
184
Oxfordshire, UK
Very concerning if an apparent software issue can prevent normal brake operation. You must be thankful the problem didn’t kick in when trying to stop in a hurry from 70 mph. Has anyone heard of anyone else having a similar experience?
 

sho12345678

Member
Jun 27, 2019
37
14
Midlands
Yes I'm just hoping it doesn't happen mid-drive.

Tesla breakdown (option 1) suggested turning up to a service centre asking to be seen, as no appointments are available anytime soon. I will try calling service (option 2) tomorrow.
 

B road warrior

New Member
Oct 27, 2020
3
0
Carnforth, Lancs.
Has anyone heard of anyone else having a similar experience?
Yes - exactly the same thing happened to me last Wednesday morning (six month old M3LR);
in my case a full reboot got the brakes working again and it has been fine ever since (touch wood!)

Seems strange that two UK owners have had this issue within a few days of each other;
no idea whether it was connected in any way, but it was the first time I had driven the car
after downloading the new UI software...
 

pgkevet

Active Member
Jul 1, 2019
1,233
1,081
mid wales
No car should ever be designed such that sofware can over-ride the driver inputs and certainly not have software as the sole method of braking. This either mean that there is a fundamental flaw in tesla design OR that as a heavy car any glitch on power assisted brakes means you really have to boot down to get a braking effect,

(at one point I had the dubious distinction of driving a knackered1952 R-type Bentley which had both cable and hydraulic brakes and servo assisted - however the sevro assist frequently failed to kick in and one got into the habit of testing the feel of the brakes prior to making any stop - one could feel the vibration of the servo in that car. If it was working then fine , otherwise it was both hands pulling on the wheel, both feet on the brake pedal and standing up to get enough weight on the darn thing - and some close escapes)

At very least here you need to check brake fluid levels and speak to soemone at a service centre and demand attention on safety grounds/loan vehicle. Also note that in emergencies it is possible to activate the parking brake by pressing the stud at the end of the gear selection lever as per the manual.
 

Dilly

Active Member
Feb 24, 2020
1,764
1,396
Norfolk
It’s not just a Tesla thing. On one occasion, I’d done a 4 mile round trip and dropped off my my next door but one neighbour in my Ioniq.
When I went to leave, all the warnings lit up including no brakes. I nursed it home and called the AA. When the guy arrived, it was fine and never did it again. Dealership found nothing particular in the error logs either!
 

pgkevet

Active Member
Jul 1, 2019
1,233
1,081
mid wales
It’s not just a Tesla thing. On one occasion, I’d done a 4 mile round trip and dropped off my my next door but one neighbour in my Ioniq.
When I went to leave, all the warnings lit up including no brakes. I nursed it home and called the AA. When the guy arrived, it was fine and never did it again. Dealership found nothing particular in the error logs either!

Again the question is whether you just lost servo assist on the brakes or a complete loss of braking effect. the former is 'almost' acceptable as a software glitch, The latter is unacceptable from software causes and about the only one-off cause might be a bubble in the hydraulic fluid. Those of us who have driven a mutitude of old bangers in decades past will have met all sorts of brake failures but those sorts don't go away on their own - master cylinder leaks, cables snapping and so forth.
 
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Electric Dream

Pilots the Millennium Milkfloat
Jul 21, 2016
1,678
2,759
UK
Again the question is whether you just lost servo assist on the brakes or a complete loss of braking effect. the former is 'almost' acceptable as a software glitch, The latter is unacceptable from software causes and about the only one-off cause might be a bubble in the hydraulic fluid. Those of us who have driven a mutitude of old bangers in decades past will have met all sorts of brake failures but those sorts don't go away on their own - master cylinder leaks, cables snapping and so forth.
You can't lose braking completely due to an electrical/software fault.
This sounds as though the electromechanical brake booster stopped operating for some reason, so similar to a traditional brake servo failing.
The brakes still work but you have to press the pedal harder.
 

AndrewGR

Member
Oct 18, 2019
390
184
Oxfordshire, UK
You can't lose braking completely due to an electrical/software fault.
This sounds as though the electromechanical brake booster stopped operating for some reason, so similar to a traditional brake servo failing.
The brakes still work but you have to press the pedal harder.

I assume that the brake pedal is hydraulically connected to the brakes via the master cylinder as in any conventional car. However, in ICE’s the servo assist is not reliant on software so far as I am aware and sudden failures are very unusual. On a heavy modern car loss of servo assist is a serious problem - to get much braking needs a very heavy pressure on the pedal, perhaps more than some drivers could provide. If this is / was a Tesla software issue, I’d rate it as a very serious one.
 

Electric Dream

Pilots the Millennium Milkfloat
Jul 21, 2016
1,678
2,759
UK
I assume that the brake pedal is hydraulically connected to the brakes via the master cylinder as in any conventional car. However, in ICE’s the servo assist is not reliant on software so far as I am aware and sudden failures are very unusual. On a heavy modern car loss of servo assist is a serious problem - to get much braking needs a very heavy pressure on the pedal, perhaps more than some drivers could provide. If this is / was a Tesla software issue, I’d rate it as a very serious one.
Lots of cars use an electomechanical brake booster rather than engine vacuum these days.
These brake boosters are controlled, in part, electrically/by software. If a fuse blows, a wire breaks, a signal is lost etc. the electromechanical assistance could be lost and what's left is the hydraulic system alone.

I think there's a general misconception that only Teslas suffer from software glitches which can affect the general operation of the car (acceleration, braking, steering...) but that's not the case of course.
Whether the loss of servo assistance renders these or any other cars dangerous and undriveable is debatable, but unless there's evidence an issue like this is causing regular loss of life, I doubt auto makers will be redesigning their braking systems anytime soon. It just doesn't happen that often and most drivers seem able to cope, as the OP did.
 
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sho12345678

Member
Jun 27, 2019
37
14
Midlands
I already had a service appointment booked for tomorrow to check my seals, which I made a month ago. I called option 2 (40 mins on hold), was told that I can change the appointment to a "safety appointment" to check the brakes, as they would cancel my original appointment otherwise since they will only do safety appointments during a pandemic.
Today I received a SMS stating to review the app. The app has a breakdown of £52.20 for a Remote Diagnosis, which would be waived if the car is under warranty, which of course it is!!
 

Electric Dream

Pilots the Millennium Milkfloat
Jul 21, 2016
1,678
2,759
UK
FYI
There has been one report of a faulty brake booster on a UK FB group in the last few days. The owner reported that the brake pedal felt dead and needed a lot of force to stop the car. He did also have warning messages though - "power braking reduced" and "hold not available",
The local SC has agreed the ibooster had a fault and they are replacing it. This is with a M3P- delvered September 2019.

I wouldn't want to jump to any conclusions, so this could just be coincidence or a totally different cause to the OP's here.
 

sho12345678

Member
Jun 27, 2019
37
14
Midlands
FYI
There has been one report of a faulty brake booster on a UK FB group in the last few days. The owner reported that the brake pedal felt dead and needed a lot of force to stop the car. He did also have warning messages though - "power braking reduced" and "hold not available",
The local SC has agreed the ibooster had a fault and they are replacing it. This is with a M3P- delvered September 2019.

I wouldn't want to jump to any conclusions, so this could just be coincidence or a totally different cause to the OP's here.
Many thanks for this.

My SR+ is similarly a Sept 19 build and I had the same error messages come up.

My car has been dropped off to my local service centre today and I was given a 70 plate model X loaner, so that was kind of them!
 

Electric Dream

Pilots the Millennium Milkfloat
Jul 21, 2016
1,678
2,759
UK
Many thanks for this.

My SR+ is similarly a Sept 19 build and I had the same error messages come up.

My car has been dropped off to my local service centre today and I was given a 70 plate model X loaner, so that was kind of them!
Sounds very much like the same issue then. I wonder if it's connected with cold weather?
 

sho12345678

Member
Jun 27, 2019
37
14
Midlands
Sounds very much like the same issue then. I wonder if it's connected with cold weather?
Yes possibly.

I did a quick search of the forums and the same error message came up for some Model S's in 2018 and was thought to be related to water ingress and upsetting the sensors/brake booster. There has been a fair bit of melted snow these last few weeks compared with the previous year, but our climate is relatively milder than North American and Scandinavian countries where the M3 is popular?
 

Electric Dream

Pilots the Millennium Milkfloat
Jul 21, 2016
1,678
2,759
UK
Yes possibly.

I did a quick search of the forums and the same error message came up for some Model S's in 2018 and was thought to be related to water ingress and upsetting the sensors/brake booster. There has been a fair bit of melted snow these last few weeks compared with the previous year, but our climate is relatively milder than North American and Scandinavian countries where the M3 is popular?
Maybe it's only RHD cars like the other water ingress issue with the steering loom?
 

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