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How's it going folks. So as the title suggests, my 17 Bolt has an occasional grinding noise when I put it in park. Typically on an incline. I've seen one other thread about this issue, but I made this new one because the other thread blamed it on the parking mechanism. I thought the same thing, because I noticed it when putting it in park, because sometimes the brake engages automatically. I have narrowed it down to the point where I know it's the parking brake, because I can replicate it using only the brake and not the park button. The dealer is stumped. They recalibrated it, and said they inspected it for damage and found nothing, but it grinded again this morning. It sounds just like an automatic transmission does when you force it into park while the car is still moving, or if you try to force a manual into gear without pushing in the clutch. Has anyone else experienced this? This is my first EV and also first car with an EPB, so what could the sound actually be coming from? I'm not happy with it... I've got half a mind to get GM to buy the car back from me. A brand new car shouldn't be making such noises.
 

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Are you holding your brake and putting the parking brake on before you shift into park? Because what is probably happening and I have heard this myself is that while shifting into park the car moves a little and it grinds against the pawls it is locking. It even says it will do that in the manual. The car will for sure make that noise on an incline if you are not holding the brake, putting the parking brake on just holds the cars weight so it isn't support by the pawls it locked into. Same as you should do in any car manual or automatic, you don't want the weight of the car supported by the transmission gears.

Page 204

Shifting Into Park
To shift into P (Park):
1. Hold the brake pedal down and
set the parking brake. See
Electric Parking Brake 0 210.
2. Press the button on top of the
shift lever to shift into P (Park).
See Electric Drive Unit 0 206.
3. The P indicator on the shift
lever will turn red when the
vehicle is in P (Park).
4. Turn the vehicle off.
 

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I, too, put the parking brake on (while at a complete stop) first and "shift" into Park second. It seems counterintuitive, but usually makes no noise at all. In all my ICE cars, I would shift into "P", then apply the parking brake. I reverse the order when starting to drive: "On", "Parking brake OFF", shift into "R" (or "D"). It simply becomes a habit that does not make you cringe at a disgruntling sound.
 

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It's not the parking brake. You are shifting to park while the vehicle is still moving. Stop the car completely before pushing the button. It's the parking pawl inside the trans that's grinding. Don't tell me you're stopped when you put it in park, because there is a TSB for this and you are the cause of it.

Not picking on you, but just telling it like it is. Stop doing this or you'll damage the things inside the trans and your warranty will not cover it when they need to replace the transmission because you damaged it.
 

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It's not the parking brake. You are shifting to park while the vehicle is still moving. Stop the car completely before pushing the button. It's the parking pawl inside the trans that's grinding. Don't tell me you're stopped when you put it in park, because there is a TSB for this and you are the cause of it.

Not picking on you, but just telling it like it is. Stop doing this or you'll damage the things inside the trans and your warranty will not cover it when they need to replace the transmission because you damaged it.
Yeah that's when I've noticed the grinding noise too when putting it in park was because I hadn't come to a complete stop. So now I make sure that I come to a complete stop before putting it in park.
 

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Discussion Starter #9
It's not the parking brake. You are shifting to park while the vehicle is still moving. Stop the car completely before pushing the button. It's the parking pawl inside the trans that's grinding. Don't tell me you're stopped when you put it in park, because there is a TSB for this and you are the cause of it.

Not picking on you, but just telling it like it is. Stop doing this or you'll damage the things inside the trans and your warranty will not cover it when they need to replace the transmission because you damaged it.
No offense taken, and thanks for your reply. However, I don't believe what you suggest is the case. I can get it to make the noise using only the parking brake while the car is still in D or L and on a hill. I'm not sure how an EPB works, is there a pawl used in the braking system like there would be in a trans?
 

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No offense taken, and thanks for your reply. However, I don't believe what you suggest is the case. I can get it to make the noise using only the parking brake while the car is still in D or L and on a hill. I'm not sure how an EPB works, is there a pawl used in the braking system like there would be in a trans?
There are no pawls on the EPB. The EPB is just a normal parking brake with an electronic actuator to engage and disengage it.

If it really is the EPB making the noise it should not matter what gear the car is in. You should be able to reproduce the noise while the car is in park.
 

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How's it going folks. So as the title suggests, my 17 Bolt has an occasional grinding noise when I put it in park. Typically on an incline. I've seen one other thread about this issue, but I made this new one because the other thread blamed it on the parking mechanism. I thought the same thing, because I noticed it when putting it in park, because sometimes the brake engages automatically. I have narrowed it down to the point where I know it's the parking brake, because I can replicate it using only the brake and not the park button. The dealer is stumped. They recalibrated it, and said they inspected it for damage and found nothing, but it grinded again this morning. It sounds just like an automatic transmission does when you force it into park while the car is still moving, or if you try to force a manual into gear without pushing in the clutch. Has anyone else experienced this? This is my first EV and also first car with an EPB, so what could the sound actually be coming from? I'm not happy with it... I've got half a mind to get GM to buy the car back from me. A brand new car shouldn't be making such noises.
I'm having the exact same problem. I believe it's the parking prawl in the drive unit
 

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I've noticed this a couple of times. Question...is your foot on the brake when you put it in park? I've noticed when I'm on an incline, even something with a low slope such as my driveway, I need to put my foot solidly on the brake, then hit P for park, then engage the emergency parking brake, then take my foot off the brake pedal.

If I just roll up to a stop and brake-and-P, if I let off the brake the car will shift a little and the emergency brake will grind while engaging.

I honestly don't think your car is defective, I think it's just a quirk of how the parking system is engineered, or how electric e-brakes are engineered in general.
 

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Once, I'm mean once, did I engage park before the car completely came to a stop. Like you said, I was on a slight incline and didn't notice the car hadn't completely stopped because I was in a hurry. What a gosh awful sound hearing the parking pawl ratchet through several teeth. After hearing that once, I vowed to never do it again. I always double check that the car is completely stopped with the brake before I'll engage park. I'll only use the parking brake if I'm on an incline. If it's steep enough, the car will do it automatically.
 

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Once, I'm mean once, did I engage park before the car completely came to a stop. Like you said, I was on a slight incline and didn't notice the car hadn't completely stopped because I was in a hurry. What a gosh awful sound hearing the parking pawl ratchet through several teeth. After hearing that once, I vowed to never do it again. I always double check that the car is completely stopped with the brake before I'll engage park. I'll only use the parking brake if I'm on an incline. If it's steep enough, the car will do it automatically.
That is not what the sound is. This has been sleuthed already in the forum, but with the new site layout I don't feel like digging up a link.

It's the sound of the emergency braking system applying the footbrake. This is the same system that the driver-assist feature uses to stop the car if you are about to run into the back of someone. It makes a horrible noise because the compressor that drives it is mostly intended for emergencies and who cares what it sounds like in that context.
 

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There are no pawls on the EPB. The EPB is just a normal parking brake with an electronic actuator to engage and disengage it.

If it really is the EPB making the noise it should not matter what gear the car is in. You should be able to reproduce the noise while the car is in park.
There is a parking pawl in the Bolt. You can see it here (link starts at the spot where you can see it):


Mike
 

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It makes a horrible noise because the compressor that drives it is mostly intended for emergencies and who cares what it sounds like in that context.
The only compressor in the Bolt is the AC compressor. I am pretty sure they aren't using AC refrigerant for braking. :)
 

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The only compressor in the Bolt is the AC compressor. I am pretty sure they aren't using AC refrigerant for braking. :)
Speaking of braking and the iBooster... I occasionally feel a ratcheting in the brake pedal when I press it after I haven't used it in a while. Is this normal? After it ratchets once, it seems to work normally after that and minus the ratcheting feel, still works when that happens even though the brake pedal feels like it goes down a little further when it happens.

Mike
 

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I went and found the thread:

And here is another point in the same video, this time from outside the car.

I think this is absolutely the horrible sound we hear. I think this is complete confirmation that it is the low-speed emergency braking system.
I'm excited and actually please to announce that.... Vertiformed is correct! Verified by testing w/pedestrian target and as well (and this is a bit of a bummer in its implications) by applying parking brake while the car is moving.

Film later. We chose poorly and our target melted in rain before we could get cosmetically acceptable footage.

What's interesting and slightly sad is that applying the parking brake control while the vehicle is underway (as described in the owner's manual) does nothing with the parking brakes at the rear of the car; pulling up the parking brake control while driving actuates the hydraulic braking system, under software control and exploiting the ABS system. I'd hoped that this car offered the same advantage as a twitch or gentle pull on the parking brake lever of cars such as our old Volvos in pulling the ass-end of the car back in line in low traction conditions. Nope. And really, with the motorized parking brakes that was never a possibility.

Anyway it's clear from testing that the car is too intelligent to attempt to ram the pawl into place before the vehicle is stopped. The actual emergency braking system (as opposed to the parking brake) is applied and makes a horrific noise while so doing. As the manual offers no cautions or warnings about thrashing the vehicle by using the parking brake while under way it seems there's little to worry about here. As Vertiformed (and others?) here have been suggesting all along.
 

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Yeah, I probably used the wrong word; that said, the iBooster has an internal motor that creates hydraulic pressure.
Sorry to harp on this. I just want folks to understand. The motor on the iBooster pushes the piston of the master cylinder just as your foot does. A motor could, of course, apply more pressure than you leg can. However, I doubt it actually does. I am pretty sure you could lock the brakes with a failed iBooster. We just don't expect to have to work that hard to stop.
 
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