Resolved - Braking Issue/PSM Failure, with Video

[WasserGKuehlt]

This may or may not help: I tend to increase my braking force at/below 6mph when the hydraulic brakes kick in. Over time this wears out the pads just a bit, and so the car needs to rerun its blending algorithm. According to the manual/tech literature posted here a while ago, that is only done when the car is charging over a longer period of time - say from ~20ish% SoC back to 80ish. After each of those charging sessions, the transition between the e- and hydraulic braking is absolutely seamless - and then it drifts slightly over the following few days.

Tl;dr: noise is definitely not normal, but it doesn't seem unsafe either. If your charging habits are to top off, there may not be a chance for re-blending to take place.

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[irrelevant]

This may or may not help: I tend to increase my braking force at/below 6mph when the hydraulic brakes kick in. Over time this wears out the pads just a bit, and so the car needs to rerun its blending algorithm. According to the manual/tech literature posted here a while ago, that is only done when the car is charging over a longer period of time - say from ~20ish% SoC back to 80ish. After each of those charging sessions, the transition between the e- and hydraulic braking is absolutely seamless - and then it drifts slightly over the following few days.

Tl;dr: noise is definitely not normal, but it doesn't seem unsafe either. If your charging habits are to top off, there may not be a chance for re-blending to take place.

Thanks. We have only charged above 85% once…at home. I don’t think we’ve gone as low as 20% in several weeks. We generally run down to around 30%-40% before plugging in, and we’ve only DCFC during one day of ownership.

I don’t think it’s unsafe, except for the lack of feedback/firmness of the brake pedal. Our e-trim behaves nothing like this, and it has a blended regeneration/friction system.

Reading others experience with similar issues, I suspect either the master cylinder or servo needs replacing, or at a minimum the brake system needs to be bled.

Hopefully we’ll make progress with the service department tomorrow. The whole “brake squeal is normal” response is beyond annoying. I’m not here as a former Tesla owner. I understand machines, and have owned high performance vehicles for decades.

 

[irrelevant]

I had a similar issue and it was the brake module. once replaced that fixed the issue.

Thanks for the information.

 

[tchavei]

This may or may not help: I tend to increase my braking force at/below 6mph when the hydraulic brakes kick in. Over time this wears out the pads just a bit, and so the car needs to rerun its blending algorithm. According to the manual/tech literature posted here a while ago, that is only done when the car is charging over a longer period of time - say from ~20ish% SoC back to 80ish. After each of those charging sessions, the transition between the e- and hydraulic braking is absolutely seamless - and then it drifts slightly over the following few days.

Tl;dr: noise is definitely not normal, but it doesn't seem unsafe either. If your charging habits are to top off, there may not be a chance for re-blending to take place.

Wasn't there a technical pdf from porsche about how to force this "reblending" during a charge? Something along going from P to D and back to P right before initiating charge? Can't remember now

 

[Moonstone]

On ICE cars the stability control system relies on the ABS speed sensors (and I'll assume that the same is true here) to work properly so the PSM error message suggests that there is definitely a fault with at least one of the braking mechanisms somewhere, so this is definitely not just "normal functional noises".

 

[irrelevant]

To update, I drove the Taycan to the dealer this morning, and met with the shop foreman. I requested he test drive it with me.

He turned the car on (that sounds kinda...), pumped the brake pedal a couple of times and said "That's definitely not right. I can't believe you drove it here like this."

I encouraged him to take it out for a drive, but he declined, saying he didn't feel it was safe. We got out of the car, and he checked the brake fluid reservoir, which seemed properly filled with fluid.

A Macan loaner was provided...which is pretty underwhelming as a vehicle, though I appreciate Porsche providing it, and that's where we are at present.

 

[jcg]

I have the same sound and feel on my 22 GTS with 17k miles. Dealer did some reprogramming and seems to be less prominent but still present. I will follow this thread with interest.

Taking the car in 1-2 weeks for the heater and will have them check brakes again.

 

[DynamoCappo]

Thanks for sharing. I'd have never thought to use the keyword "goat".

I got an insulting e-mail from the service advisor that read this is normal, and "brake squeal" is to be expected. ? I had to wait a few moments to cool down before responding.

I didn't realize in error I'd checked the option box for "service department that assumes you're a moron".

I've had the exact same situation happen in the last few days.

On Thursday, I slowed down and felt, at 5mph, the pedal seemed to go spongy.

Driving home it was the same. On Friday, it started making the noise which is perfect described by the word goat.

Had minimal driving over the weekend but it was the same.

This morning, driving to work, I had the PSM warning come on identical to yours.

I'll be phoning the workship in 20 minutes. The information you've provided so far will be invaluable to my first words with them. Hope you're making headway with it all.

As an aside, I've done 1500 miles in mine and the green regen light hasn't kicked in at all yet.

I'd posted on another thread about it last week.

https://www.taycanforum.com/forum/threads/strange-braking-issue.4818/page-3#post-241946

 

[DynamoCappo]

@irrelevant

As an update for you...

I was asked to come in to the dealer so they could run a diagnostics check.

Having done that, they asked me to wait for an hour or so so they could perform a break bleed.

Mechanic said this would one of potentially two or three things which eventually need done.

I explained that my green regen light has never come on yet and he said it usually does around a few hundred miles.

I'm guessing none of that has come into his thought process following whatever plan they're working on just now.

I'm guessing I'll be back in at some point.

I've still to have my full Masterclass tutorial as part of the handover process as I didn't have time on the day of collection.

Can see me having a list of questions to ask them about regen when I come back in to do that if whatever they're doing just now doesn't force start that by coincidence.

 

[dtich]

The whole “brake squeal is normal” response is beyond annoying. I’m not here as a former Tesla owner. I understand machines, and have owned high performance vehicles for decades.

As a (soon to be former) Tesla owner and an understander of machines and owner of several high performance vehicles, I object to that characterization. At least 10% of Tesla owners know what they're talking about.

Brake squeal, as all us high performance vehicle owners know, is sometimes inevitable given some braking habits. The only real way to avoid it is to use the brakes as brakes want to be used, hard and consistent on the attack, ease off as you accelerate, and don't, for the love of all that is holy, *ride* the dang brakes (I'm looking at you: almost all drivers out there), this will glaze them and then that sound will never go away until you change the pads and re-bed. The braking system in the Taycan may make the pads' bedding-in period much longer because they are lightly used. Obviously P is trying to ameliorate this issue by setting a bedding-in period where recuperation is not used. However, and I'm not sure about this, if you drive in Sport mode recuperation is always used so this may contribute to pads not wearing-in properly. I'd say the real solution is just drive the car harder here and there and get those pads up to temp.

 

[dtich]

To update, I drove the Taycan to the dealer this morning, and met with the shop foreman. I requested he test drive it with me.

He turned the car on (that sounds kinda...), pumped the brake pedal a couple of times and said "That's definitely not right. I can't believe you drove it here like this."

Definitely curious as to what this ends up being. It feels like the Taycan braking system is especially susceptible to bleed and use conditions. I think the blending algorithm is just not good enough. And perhaps it's not a good idea for how to blend the two braking systems in the first place.

It is curious that the e-tron seems to have the same system but many fewer reports of this issue, am I right about that?

If this does turn out to *really* be the MC or some other component that's .. crazy. How many component failures can there be in the world? Did manufacturing prowess and QC take a nose-dive in the past 5 years? That's a rhetorical question. I think the answer is clear.

 

[WasserGKuehlt]

Definitely curious as to what this ends up being. It feels like the Taycan braking system is especially susceptible to bleed and use conditions. I think the blending algorithm is just not good enough. And perhaps it's not a good idea for how to blend the two braking systems in the first place.

This past weekend I had the "opportunity" to charge overnight from below 20%SoC to 80ish. The next day the brake pedal felt amazing - consistent throughout, so much so that I couldn't help myself and did several full stops.

The corollary is that the algorithm itself is damn good, but the usability (or intuitiveness) of it is lacking. I don't know why they considered a long/deep charge to be a requirement for rebalancing the brakes. I can't imagine it would put the car into an 'unsafe' condition (and thus needed uninterrupted time to converge back).

 

[dtich]

Very interesting. I had thought it must have been a good algo because I assume the foundation of it comes from their e-racing experience. In a racing development environment this system probably performs exceptionally, but as you say, in the real, normal-day, grocery store shopping use case... not so much.

So all it needs is a good long charge session, huh? Hm. Seemingly, this is a master-cylinder calibration thing, where it measures the available brake pressure to pedal travel curve? I suppose this enables it to choose the precise points where mechanical cuts in.

Found this, which says something about the system, but nothing very specific.

https://newsroom.porsche.com/en/202...ke-force-distribution-recuperation-30953.html

Seeing the graphs here and reading it, I get the idea a bit more, but honestly, somehow it feels maybe a little too complicated for a braking system. Really, really relies on this calibration session and realtime calculations to make brake feel smooth and precise.

 

[WasserGKuehlt]

Very interesting. I had thought it must have been a good algo because I assume the foundation of it comes from their e-racing experience. In a racing development environment this system probably performs exceptionally, but as you say, in the real, normal-day, grocery store shopping use case... not so much.

So all it needs is a good long charge session, huh? Hm. Seemingly, this is a master-cylinder calibration thing, where it measures the available brake pressure to pedal travel curve? I suppose this enables it to choose the precise points where mechanical cuts in.

I think it deviates continuously, and depending on one's driving style, with major factors being brake pad wear and any inefficiencies in the hydraulic circuit (ie air, higher water content etc.) The rebalancing is probably done, as you say, at the master cylinder regulator - and presumably they need a long, uninterrupted time to sample the brake pedal's travel (or to simulate it). Then adjust, measure again etc.

Seeing the graphs here and reading it, I get the idea a bit more, but honestly, somehow it feels maybe a little too complicated for a braking system. Really, really relies on this calibration session and realtime calculations to make brake feel smooth and precise.

And it works - I don't think there was ever a time when complexity stopped Porsche. You should see, if you haven't, what a 944 turbo looks like under the hood ?.

 

[dtich]

Copy. That.

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