nozferatu
Posts: 575
Joined: Sat Feb 01, 2014 4:47 pm

Possible Regen Brake Issue

Mon Apr 07, 2014 1:43 pm

Hey everyone,

Only had the car three weeks and today my car developed a very unusual brake problem.

While stationary, if I press the brake pedal, I hear a loud clicking sound coming from the front area...it's like a solenoid almost clicking on and off. I also hear a constant a weird electrical "circuit" type of sound...almost as if there's intermittent connection/etc sort of thing. This is all in Park.

The sound is quite loud when I press the pedal...clicking and a weird almost grinding sound.

When in motion and rolling to a stop say from about 5 MPH, I feel the click and then a weird grinding sensation for a second or two and then it goes away.

I'm really bummed to say the least. Barely had the car. It doesn't seem to affect braking performance or anything like that but clearly it's not normal. This thing was whisper quiet just prior to this morning.

I've had to use the brakes a few times times relatively forcefully but if this thing falls apart so fast after a couple of hard stops, this isn't good.

Any suggestions? I've got no codes thrown and Onstar did a diagnostic that came out clear.

I'll be taking it to the dealer but it'd be interesting to hear from others if they've ever experienced this.

nozferatu
Posts: 575
Joined: Sat Feb 01, 2014 4:47 pm

Re: Possible Regen Brake Issue

Mon Apr 07, 2014 1:46 pm

Oh and one other thing. I really REALLY hear and feel the gear shifter release mechanism now when pressing the brake in order to move the shifter out of P.

Very weird.

markcmann
Posts: 145
Joined: Sun Jun 23, 2013 9:31 pm
Location: Southern California

Re: Possible Regen Brake Issue

Mon Apr 07, 2014 8:01 pm

Yep, I know exactly what you mean, I posted about this when I first got my Spark EV:
http://www.mychevysparkev.com/forum/vie ... f=9&t=3421
This is just how the brakes work, not the most elegant design but there is nothing wrong per se with the braking system.

Nashco
Posts: 537
Joined: Wed May 29, 2013 12:00 am
Location: Portland, OR

Re: Possible Regen Brake Issue

Mon Apr 07, 2014 8:21 pm

Are you sure you're not hearing the brake booster pump? While stationary, press and release the pedal multiple times. Every once in a while you'll hear and feel the booster pump run for a few seconds and then turn back off. This is normal operation. The pump only runs as needed rather than constantly, which would make it seem intermittent.

As for the click sound, are you sure that's not the brake light switch and/or or park release solenoid? Again, these make noise normally in any car. With the radio off and no engine noise, it's much more pronounced than any other car you've had before.

Your description is a little tough to follow with multiple separate issues in one description.

Bryce

nozferatu
Posts: 575
Joined: Sat Feb 01, 2014 4:47 pm

Re: Possible Regen Brake Issue

Mon Apr 07, 2014 8:59 pm

Hey Guys,

Yeah I am 100% sure this isn't normal...it wasn't happening until this late morning. I can assure you the car was silky smooth and the brakes felt OK if not different than a regular car...but there were no sounds, not thumping, not clicking. Bryce I know what you are talking about when you press on the brake in P and the gear shifter solenoid releases the shifter...that's not it.

This is what happens when I lightly press down on the brake pedal:

It sounds and feels like it clicks...like what you'd feel if a solenoid switched open or closed.

If I continue to press down this is what happens:

A sharp twanging sound occurs...like a spring or piece of metal has been bent and then springs back.

When on the move...say at 3-4 MPH and coming to a stop, this is what happens:

I feel the click...and then it feels like the brakes are grinding...and then the twang..loud enough that the service manager and shop foreman clearly heard and felt the sound and twang.

This DID NOT happen ever since I bought the car.

Another thing that really was tough to hear but I could clearly hear it when in my garage and outside noise was muted was the following:

I hear a squeaking...electrical squeaking sort of sound...like a circuit that is not functioning properly and you can hear it emit a high pitched, variable pitch sound...and this is in P or N where the car's external warning sounds are off. This car was whisper quiet prior to this.

This may turn out to be a bad solenoid...hopefully. But it clearly is something that has gone bad or failed. Brake performance didn't seem to be affected.

The only thing I sincerely hope for is that they don't tear the car apart. I really do not want a brand new car given back to me after being opened up....I'll ask for a new car if that's the case.

nozferatu
Posts: 575
Joined: Sat Feb 01, 2014 4:47 pm

Re: Possible Regen Brake Issue

Mon Apr 07, 2014 9:02 pm

Mark,

I think what you are talking about is the transfer from regen braking to actual hydraulic braking. That's normal and I feel that transition too...but what I'm experiencing is far more obvious and different than that.

Skullbearer
Posts: 25
Joined: Sat Mar 15, 2014 6:47 pm
Location: Sacramento, CA

Re: Possible Regen Brake Issue

Tue Apr 08, 2014 8:10 am

Definitely not a normal sound or feel, but it probably is related to the blended braking system.

You can replicate the 'correct' sound of this change by using moderate regen braking at speed (say 45mph) and then shifting to N. The vehicle makes a very slightly clunky transition to 100% hydraulic brakes, but has almost identical feel after transition. The sound and feel are not nearly so severe that they would cause alarm, and everyone should do it at least a couple of times to know what's 'normal' (I did it on accident the first time). Blended braking is a very difficult process to manage, both mechanically and software wise, so I think Chevy did a fantastic job with it so far. The vehicle makes the transition gradually from some set speed during normal continuous braking... usually from around 6mph down to 2 or 3 mph. Reliable and efficient torque control in a PMAC motor begins to become very difficult at very low speeds and can cause a jerky braking feel, so the transition to hydraulic braking keeps it smooth. On your problem it either has to be a bad controller, bad electrical connection, or most likely a bad blended braking system (the electro-mechanical portion, which may be a solenoid or other proportional valve inline with the master cylinder output, or even the master cylinder itself). I don't know what unit Chevy used, but Bosch recently began selling a production blended braking unit that acts as the master cylinder and provides the same feel as if you are actually braking, but controls the actual pressure output to the brake system. The Bosch unit is the only 'off-the-shelf' system that could do the blended braking style that the Spark has, so I'll be it's what we'll find in our vehicles. Given that it's a very new product, we should all keep an eye out for failures... worst case though, the system 'should' fault to an open bypass state... ie 100% hydraulic brakes.

If your dealer is having trouble diagnosing it, they should start by checking the wiring harness to the blended brake unit, then replacing the unit itself, and finally with a controller replacement. If it starts happening above 6mph, pay attention to whether or not the electric power meter suddenly goes to no regen even though you're braking, it could be falsely detecting an N position on the shifter.
Development Engineer
EVs, PHEVs, CVTs, ECVTs (Don't know it, look it up!)

High Voltage and Low Voltage;
They both bite, but only one is a funny story. Don't mess with the orange.

nozferatu
Posts: 575
Joined: Sat Feb 01, 2014 4:47 pm

Re: Possible Regen Brake Issue

Tue Apr 08, 2014 8:32 am

Skullbearer wrote:Definitely not a normal sound or feel, but it probably is related to the blended braking system.

You can replicate the 'correct' sound of this change by using moderate regen braking at speed (say 45mph) and then shifting to N. The vehicle makes a very slightly clunky transition to 100% hydraulic brakes, but has almost identical feel after transition. The sound and feel are not nearly so severe that they would cause alarm, and everyone should do it at least a couple of times to know what's 'normal' (I did it on accident the first time). Blended braking is a very difficult process to manage, both mechanically and software wise, so I think Chevy did a fantastic job with it so far. The vehicle makes the transition gradually from some set speed during normal continuous braking... usually from around 6mph down to 2 or 3 mph. Reliable and efficient torque control in a PMAC motor begins to become very difficult at very low speeds and can cause a jerky braking feel, so the transition to hydraulic braking keeps it smooth. On your problem it either has to be a bad controller, bad electrical connection, or most likely a bad blended braking system (the electro-mechanical portion, which may be a solenoid or other proportional valve inline with the master cylinder output, or even the master cylinder itself). I don't know what unit Chevy used, but Bosch recently began selling a production blended braking unit that acts as the master cylinder and provides the same feel as if you are actually braking, but controls the actual pressure output to the brake system. The Bosch unit is the only 'off-the-shelf' system that could do the blended braking style that the Spark has, so I'll be it's what we'll find in our vehicles. Given that it's a very new product, we should all keep an eye out for failures... worst case though, the system 'should' fault to an open bypass state... ie 100% hydraulic brakes.

If your dealer is having trouble diagnosing it, they should start by checking the wiring harness to the blended brake unit, then replacing the unit itself, and finally with a controller replacement. If it starts happening above 6mph, pay attention to whether or not the electric power meter suddenly goes to no regen even though you're braking, it could be falsely detecting an N position on the shifter.
Hey Skullbearer,

Thanks for the input. It's a bit disconcerting that the dealership has only ONE certified tech on hand for the Spark EV..which makes me concerned to be honest. But I hope it's an easy fix and they don't have to tear the car apart.

I also get the sense that it may be a bad electrical connection because as I said earlier, I hear a faint but definite variable pitch electrical "circuit" type sound emanating from the front wheel arches/areas...while in P or N.

I've actually forwarded this posting you wrote above to the shop foreman as I think it's a great starting point for them.

My problem is definitely most noticeable at low speeds...5 MPH and below...with perhaps coming to a stop or in N or P allowing the problem to be most noticeable. It's quite loud...the twanging and clicking. And when coming to a stop, the transition feels like there's a grinding feel.

nozferatu
Posts: 575
Joined: Sat Feb 01, 2014 4:47 pm

Re: Possible Regen Brake Issue

Tue Apr 08, 2014 9:13 am

Quick question to all.

Could accelerating rapidly and then decelerating rapidly cause any of these modules/systems to overload and fail?

Essentially the problems started when I had to accelerate very hard and then lift off quickly and apply considerable brake force. I was in L when all this happened.

But the issues didn't start until about 5-10 minutes after.

Skullbearer
Posts: 25
Joined: Sat Mar 15, 2014 6:47 pm
Location: Sacramento, CA

Re: Possible Regen Brake Issue

Tue Apr 08, 2014 3:00 pm

nozferatu wrote:Quick question to all.

Could accelerating rapidly and then decelerating rapidly cause any of these modules/systems to overload and fail?

Essentially the problems started when I had to accelerate very hard and then lift off quickly and apply considerable brake force. I was in L when all this happened.

But the issues didn't start until about 5-10 minutes after.
Could is a difficult question to answer, because failure modes can be very complex, especially since I wasn't part of the design team and don't know it well.

But, that is well within expected operation, it SHOULD NOT have caused any problem (even if it did). Should not, as in warranty covers it very clearly with zero liability on your part. Should not, as in the law requires it to be able to operate repeatedly and for any designated minimum maintenance interval under those types of conditions for the vehicle to be sold.

When you exceed the maximum allowed regen braking, you go into hydraulic braking for all additional, but at most all you did was push an already faulty component past that breaking point.


Again, don't feel like you did it at all, this is absolutely and without question something that should be covered in any vehicle design. There are many regulations and SAE standards regarding braking performance and range of operation that Chevy is required by law to meet and hold liability for. Whatever you do, do NOT take liability, express a sense of liability, or allow a service person to assign to you liability for this failure. It may or may not happen at some point in getting this addressed, since this failure should be reported to Chevy engineering support for evaluation (who will not want to express liability on Chevy's part). They'll probably want to pull your entire blended braking system for engineering evaluation, if they do not find visible or detectable problems. This means of course that they'll also need to put in a completely new unit. If they start to harass you and try to assign liability to you, I'd consult a lawyer... but it rarely comes to that. You have the recent recalls on your side in this, they will likely bend over backwards to fix this thoroughly and quietly.

I hope it goes quickly and painlessly, either way!
Development Engineer
EVs, PHEVs, CVTs, ECVTs (Don't know it, look it up!)

High Voltage and Low Voltage;
They both bite, but only one is a funny story. Don't mess with the orange.

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