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Yeah, the lack of business doesn't make honesty easier. dealers should be aware of these bulletins, since GMProduct Quality Center put a parts restriction on parts involved in this issue on October 8,2018 with mfr. communication #PIC6234A ! It's got an NHTSA ID #10147356 too. Fortunately doesn't seem to be a safety issue, even tho it is a brake system issue.
 

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Thanks to everyone who tracked this down. This is the best forum for Bolt technical explanations.

I'm in the same boat as most people here. I've got a 2017 Premier with 22K miles on it, and of course it's 4 months out of the 3/36K B2B warranty. Definitely confirmed all the usual symptoms:
  1. Clicking starts upon car unlocking
  2. Stops immediately when the brake pedal is pressed
  3. Shorter duration or completely absent clicking noises in cold weather vs hot
  4. No noticeable range degradation or braking performance when using the regen paddle
How we will find out that the 1Q 2021 SW patch promised in the bulletin is available?
 

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My 2017 (now out of the 3 year warranty) is having the same iBooster issue.

I have been having this long email discussion with GM corporate over this issue as I believe the iBooster should be covered under the 8 year warranty, 100K warranty period. Here is my logic for this:

If you look on page 323 of the 2017 Bolt's owner manual, it states that the Brake Modulator Assembly is covered "During the 8 years or 100,000 miles (160 000 kilometers) Hybrid warranty period". This includes:

Brake Modulator Assembly
Electric/Hybrid Drive Unit
Electric drive unit assembly electric
motors, and all internal components,
including the auxiliary fluid pump,
auxiliary pump controller, electric
motor, and 3-phase cables.

Now (and you need to stick with me here) on page 17 of the Canadian Limited Warranty and Owner Assistance Information of the 2020 bolt they define the Brake Modulator Assembly thusly:
The Brake Modulator Assembly,
used for regenerative braking, is
covered for the duration of the
Electric and Hybrid Vehicle
Warranty coverage period.

The iBooster is definitely used for regenerative braking. It is one of its main functions. So I believe the Brake Modulator Assembly is the iBooster (and maybe some other stuff).

GM Corporate said I needed to go to my local Chevy dealer (Martin Chevrolet) to make sure my tap tap tap was, in fact, the iBooster. Here is the crazy part. The service intake guy had no idea what I was talking about, so he asked a technician (Dennis) walking by. Dennis said "2017 Bolt? Tapping? Yup, iBooster, needs to be replaced". Then my service intake guy said "Ill need $199.00 diagnostic fee for me to write that down for GM Corporate".

Huh?

Bottom line, I so hope I can get this fixed with a software update in 2021. Maybe they fix the "my Bolt is on fire" issue at the same time while keeping my range. We can hope right?

Thanks again for those tracking this all down. Love, love the car! EV's are just a far better way to get around.
 

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The recommended action for this problem is a software update. No parts should need replaced.
The only issue with this is that it doesn't seem that the iBooster values are in an idle position (or whatever). It is more like a pump hammering away. May not cause any issues with the iBooster but it is not a rattle. Rattles are random. This is a very consistent (annoying) tapping.

Still, I hope they can fix it via software. And wouldn't it be nice if they could fix it OTA? And even the "hey, is that our Bolt burning?" problem via OTA. Oh to dream.
 

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OTA, let’s dream on. I have had two replacements under warranty, now the thumping is back. My Chevy Advisor is “reviewing “ the situation, especially when I mentioned to him that a Software Update might be available.
 

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thanks for the note about the effect of lower temperatures reducing the tapping noise. Down in the 30's it disappeared.
My dealer took about $1000 in advance to order the part (FP # 42698893) on 11/28. As of 112/11 it hasn't arrived.
NHTSA has a notice #10147356 and mfr #PIG6234A on this Bosch brake booster.
I can’t find the NHTSA #10157356 notice on there website .
 

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2017 Chevy Volt has same problem, repeatedly

I live on Kona side of Big Island. Dealer is 2 hour drive down mountain to Hilo side, each way. I have had the entire brake assembly replaced twice, but noise keeps returning. GM Customer Care is awful (they seem clueless on anything technical), as is Dealer. The only mechanic certified on Chevy electric vehicles (who has done the first 2 replacements told me he replaces brake assembly often on both Bolts and Gen 2 Volts for this reason, yet GM Customer Care claims they have no other alerts on Regen Braking assembly). The actuator makes this clicking noise once you activate electronics in car (open door, use FOB). It is loud and lasts until you start using brake pedal. If brakes are hot, the actuator won't make clicking noise. That means I must wait a couple hours before proving to Dealer that the problem has returned, whihc forces me to stay overnight in Hilo.

I had to drive it over again and rent hotel, as Gm insisted. Now, I will return later thsi month to try my third repalcment of brake assembly. I have run up large hotel bills on several trips to get this fixed. Given the history, I dont think GM will be able to fix it. No one would ever buy my car when I explain to them that the nosie is do to design defect in brake assembly that appears to not be amenable to repair. Has anyone filed a lemon claim because of this problem.

PS: I wont let my wife drive car because we live on side of volcano, with heavy need for brakes. She is not a great driver and would freak out if brakes failed on the mountain. As result, we have driven the car very little. I have bought many GM cars. I am really impressed by the Volt technology. But, this brake problem is serious and GM cant seem to fix it, as actuator noise returns within 2 months of replacing the entire assembly. Has anyone else had success with installing a new assembly? Very unhappy with this car
I am experiencing this on my 17 Bolt now and I live in Hawi. Headed to Hilo next week to get it looked at. any advice?
Thanks,J-man
 

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I am experiencing this on my 17 Bolt now and I live in Hawi. Headed to Hilo next week to get it looked at. any advice?
Thanks,J-man
I would print and take the TSB with you and ask to make an appointment for when the software update is released for the 2017. Or, if your trip is only for this issue I would wait until they have the new software to be able to fix it first. Is this vehicle new to you or did you have this issue and search for it and find the forum?
 

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Just as an added insult on this, GM got back to me and told me that the iBooster has nothing to do with the traction battery so it isn't covered under the 8 yr / 100K mile Warranty. Not involved in charging ... so there you have it.
 

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This problem is really starting to get on my nerves so I wanted to make sure what I read about there being a pending software update was not just my imagination.
So I wanted to post what I found, based on rdae/JamesD's image posted above. Don't get too excited though; this doesn't add much info but here:

This earlier Doc covers 2019-2020 -> https://static.nhtsa.gov/odi/tsbs/2020/MC-10181700-9999.pdf
This later (Dec) Doc covers 2017-2020 -> https://static.nhtsa.gov/odi/tsbs/2020/MC-10187395-9999.pdf

The December doc is from: 2018 CHEVROLET BOLT 5 HB FWD

If you look for manufacturer comms for 2019 bolts you get the earlier doc that just covers 2019-2020 which makes sense.

Anyway as mentioned in the above image posted, for 2017-2018: New software will be released at the end of the first quarter in 2021, which will eliminate the clicking noise. And 2019-2020 apparently already have a software update ready.

If this works out it'll be a nice solution as I was really bummed reading about owners having it replaced under warranty (but like a $1200 part!) and having it recur.
 

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I am bringing my 17 Premier, next week, to a new dealership, since with discussion with a service manager they apparently have the software update.
I will report to the Forum with my results.
Also a 2017, but have had only one episode, and that was quite recently. No repeats yet. Way past basic warranty; haven't checked, but possibly the extended that I bought would cover if needed. Will be interested in your result.
And thanks, also, to previous commenter for the bulletin document.
 

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I have a 2017 and unfortunately didn't start hearing the noise until the basic warranty period expired. I called corporate and my dealer to get the repair covered under the battery warranty. No luck. Eventually, the sound was more apparent, and I even felt the brake regen was "softer" (maybe it was just me). Fearing this was a safety issue, I brought it in last summer and the dealer, per their diagnosis, replaced the brake booster (fyi, the vehicle was at 40k miles; the part has a 2-yr unlimited mileage warranty). Cost me $1475 (parts and labor). Everything is working well (knock on wood). I'm glad to hear there's a potential software fix so owner's can avoid this expense.
 

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In my judgment, this is a very common defect, especially in 2017 Bolts. This should not be a charge, there is a systemic problem with either the brake booster module and/or the software to this module.
Mine has been replaced twice, thumping-tapping sound returned 10 months later each time.
This week, I’m taking it in, to a different dealer, for research and hopefully “software Update”.
More info to follow...
 

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My Bolt has the tapping issue now. 2017 with 46K miles.

Open door or hatch or plug in charging cable => Mr/Ms Woodpecker. I'm very grateful for the posts on this forum describing this problem, particularly the TSB information. Today I filed my complaint at NHTSA on this issue (File a Vehicle Safety Complaint | Safercar.gov | NHTSA).

It started mildly a couple of months ago and would cease upon tapping the brake pedal. Then required a couple of taps. Progressed so that it will go on for a couple of minutes even while driving. Tapping is useless now. Resistance is futile.

In January I called the dealer who said they had to see it before ordering the part. And a deposit would be required. And that they would have to do the recall battery software 90% fix if I bring it in. And that the time frame for getting the part was indeterminite. I decided to stick with hill top reserve for now.

Glad I did, since I see that Q1 2021 may bring a charging fix that does NOT reduce range and perhaps the I-Booster firmware fix can be done at the same time.

If there really will be a firmware fix for the tapping, want to guess how many owners will get refunded for those replacement parts (sometimes more than once)?

Thank you all!
 
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