Reducera braking performance detected (by car)

[thebishop]

When braking hard (abs kicks in), the car now shows a warning message about reduced braking performance (see pic).

anyone knows what the root cause of this warning is?

it was warm outside, running with soft winter tires, brakes seems to work as expected, but concerned the warning is due to some imminent failure in the braking system.

Anyone who’ve seen this and knows what it means? The warning is not exactly crystal clear as to the origin of the problem.

this is a 2015 p85dl (with brakes/rotors replaced a couple of years ago to winter kit from Tesla).

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• thebishop
• Dec 30, 2019

Reduced braking performance warning

 

[Az_Rael]

When was the last time you had the fluid checked? If it has been a couple of years, it might have water in the lines. My old P85 used to get that - the brake pedal would feel spongy over time.

 

[thebishop]

They should have changed the brake fluid one year ago as part of the final (year 4) maintenance that was prepaid. Who knows if they did, it was a single line item on the invoice (8000km service done).

 

[beatle]

I am curious about this error as well. I don't have it, but I feel my brakes are pretty spongy and lame. I don't think there are any sensors for brake fluid health, but it could be low. As the pistons extend, the fluid leaves the reservoir and it could trigger a low brake fluid warning which in turn warns about braking performance.

 

[thebishop]

Spongy: might want to check if you have the updated pads for cold climate if applicable.

I think the warning should have been more specific if the car knows brake fluid level is low.
I booked sc visit to get an answer...

 

[thebishop]

There are both updates to rotors and pads depending on your vehicle age.

just replacing the pads to the new ones made a big difference for me.

 

[thebishop]

The parts were:

FRONT BRAKE PAD SVC KIT HP1000-T (1055066-00-B)
MX and MS REAR BRAKE PAD SERVICE KIT (1068331-00-A)

(I had new rotors)

 

[dark cloud]

I am wondering if the car will always throw a warning message anytime the abs kicks in? I don't recall because maybe the 2 times I have braked that hard my eyes are on the road. I am wondering how you are able to take a picture of the cluster when braking that hard? But with snow tires on a wet and sandy road it would not be that hard to do.

How do the brakes feel? On a dry road with the tires warmed does it feel like you are getting decent deceleration/stopping power? With 2 year old rotors and pads, and 1 year old brake fluid they should feel good; not as good as all seasons or summer tires of course but you should still be able to pull 0.7-.8 g's.

Check the brake fluid level, but I'm pretty sure the car would throw a more specific warning for that. In 2 years of trolling around I haven't read anyone having any problems with the model S master cylinder or brake electronics; and like the general public some of these guys haven't touched the brake system for many years and don't do any maintenance until they hear grinding sounds or feel the high speed vibrations of warped rotors.

Let us know what it was!

 

[thebishop]

If it always happens for abs it is a new thing - we see plenty of abs action and I’ve never seen this message previous 4 winters.
After braking the message is up for a couple of seconds, so not hard to get a pic safely if you know it’s coming...

the brake feel is just fine (and with summer tires a couple of months ago stopping power just fine too) - and now with winters on they do stop reasonably (they manage to get the abs to kick in, so up until grip threshold with no problem), estimated to 0.8g during annual car inspection (who also was first to notice the warning message) - Before the switch to the winter climate capable brake pads in spring 2018, it felt mushy/spongy, but no longer.

Will report back when SC gives feedback - if it wasn’t such a crucial safety system I’d just ignored it, but I do want brakes that works to the best extent possible for obvious reasons.

 

[hooky]

Hi thebishop,

I've just had the same on my 85D for the first time. Winter tyres, about 0C, I noticed the car was a little slippery when moderately braking before a corner (no message or ABS) and put it down to a small amount of damp/ice. I wanted to check the conditions so waited until I was on a quiet straight and did a semi-emergency stop and then I got the exact message you have.

Tried a few more times, with full on emergency stops and some slower braking and I think your guess about ABS could be right - it only came on when the ABS kicked in - if I kept it just below ABS then no message. Also, and I guess you've already checked, no permanent error message, just the temporary one for a second or two after braking finished. I've always been under-impressed with the Model S brakes, but they didn't feel any weaker than usual.

I had a brake inspection at an independent garage a couple of months back (had a parking brake failure, separate issue) and they were perfectly happy with the state of all the (non-parking) brakes and fluid.

I'd be interested to hear what the SC came back with, but think it's probably updated software from last winter and is a new message when ABS kicks in, like you postulated.

 

[thebishop]

Ok, back from service now - tech reproduced with mine as well as two other cars in same VIN range - he thought it was possible they updated the sensitivity in a software update displaying the warning - which according to him is works as intended - it is supposedly a farming that the ibooster kicked in (not ABS). I asked to provide feedback to the sunshine boys at engineering to please not display warnings when things works as intended - wasting both my time and money as well as the tech. At least I got the annual lubrication and cleaning for cold climates done... the tech said that warning usually would come if you had snow/ice buildup and not getting decent braking performance at higher speeds. Now, we both reproduced it at 25-30 mph during perfect weather conditions. A Norwegian guy supposedly got the same warning due to a defect ibooster, so it really is a software fail here.

 

[SSedan]

I would dismantle the brakes and clean up the caliper to pad backer mating surfaces.

I can't say I have seen it in specific relation to this error but what happens is the pad binds in the caliper no longer self adjusting. The piston flexes the pad to make contact with the rotor but this travel gets ever greater as the pad wears. This results I. Excess pedal travel as the slack is taken up.

 

[beatle]

I actually received this message this weekend. I was doing some repeated acceleration tests and needed to bring the car to a stop to make another run. The car was mostly stopped when it came on, but the scary thing was the pedal dropping a couple inches. It did not hit the floor, but it did drop significantly. I'm guessing I'm due for fluid anyway.

 

[crunchtime2k]

Same message here on a new 2020 performance s when abs kicks in on dry roads.

 

[derichio02]

Same message here on a new 2020 performance s when abs kicks in on dry roads.

+1 I’ve experienced it once as well when braking hard

 

[kskog]

Just got this warning when braking hard. 2019 Model S Performance.