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2017 Chevy Bolt LT
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My Bolt's power delivery system failed somehow on May 1. The first thing I noticed was that at 2:53 PM (I have a dashcam with a timestamp) the regen brakes didn't do anything so the tires squealed when I tried to do a turn at 30 MPH and I had to use the friction brakes. I know regen braking doesn't work when the battery level is too high but it was only at 25% at the time. I didn't think anything of it until sometime after midnight when it said "Propulsion Power Reduced". At that time I was going downhill at 80 MPH on an interstate with a power usage of 1 kW, so I assumed that it estimated that it would take too much power to maintain that speed when the road became level. I didn't think it was a problem until the next day when I tried to charge at a Level 2 charger and the "check engine" light was on and it wouldn't go past 35%. I used an OBD reader and it said the error was code P0BBD so I looked it up and it said that it meant there was too much variance between cell voltages. I checked the cell voltages and they were almost exactly the same so I thought it was a transient error and tried clearing the code. It came back within a few minutes and still wouldn't charge higher than 35% so I drove home and took it to a Chevy dealer the next day.

At the dealer, they said that no EV technicians were available that day but they got me an appointment for 7:30 AM on May 5. I took it there and I've been in contact with them by text since then and I also went in person a few days ago to discuss what was wrong. While I was there, the mechanic I talked to confirmed that the cell voltages were fine and said that they were still talking to the engineering department at GM to try and find a solution. He also said that they haven't encountered this issue before but since I've seen posts about this error code, I assume he's referring to the code being shown when there's not really a problem.
 

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2022 Bolt EUV Premier
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157 Posts
Wow. Apply brake and accelerator at the same time at low speeds. Maybe. Not sure. We're working on it.
That sounds like an honest assessment from a software developer. It's kind of interesting that it made it into an actual service bulletin though. I'd imagine that the brake/accelerator combo might cause higher current but still you wouldn't think it would cause enough to unbalance the cell voltages. I can't see any good reason to be pushing both the accelerator pedal and brake at the same time. Perhaps the fix is to immediately trust the brake if it is pressed - nullifying any accelerator input. That's what I'd expect out of an EV anyway. Fighting the accelerator with the brake is just silly. Is there some use here I'm not seeing? Why would anyone push them both in an EV?
 

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I can't see any good reason to be pushing both the accelerator pedal and brake at the same time. Perhaps the fix is to immediately trust the brake if it is pressed - nullifying any accelerator input. That's what I'd expect out of an EV anyway. Fighting the accelerator with the brake is just silly. Is there some use here I'm not seeing? Why would anyone push them both in an EV?
Perhaps out of habit to prevent from rolling back when stopped in traffic on a steep hill? City of San Francisco has plenty of these. If someone is stopped really close behind you and you're facing uphill at a stoplight...

For others, some people are two foot drivers w/automatics? Don't get me started on a thread on Teslamotorsclub on this where a few people actually advocated doing this. In the past, I'd seen non-Bolts where it seems like someone is riding their brakes or they have brake switch/electrical probs. Brake lights come on a lot or are even on as they're accelerating.

BTW, you can find some "TMC" threads on the above by Googling for site:teslamotorsclub.com two foot driving and site:teslamotorsclub.com left foot braking.
 

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So, took my bolt to the dealer. I got a call later that morning that the car shouldn't be driven and should be parked. They don't know the exact problem and they are waiting for a report from the Detroit engineers. They said they would provide a rental for us. I just had the battery update in Feb and haven't had any issues since. This is very discouraging.
 

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There are some spurious cases of P0BBD without a true battery cell problem, apparently.

The attached pic was posted at
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Page 2 w/more interesting info was posted at
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. Attaching below.
Font Material property Parallel Paper Paper product


For that guy, he also included another page showing his "Hybrid/Electric Vehicle Battery Pack Voltage Variation Exceeded Limit - Battery Cell" was "failing" with cell 40.
 

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I wonder if driving with both pedals pressed can cause sufficient voltage sag (delta/imbalance from the rest) in one or more of those specific cells to incorrectly (?) trigger their software.
 

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12/16 build, 2017, white LT
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I wonder if driving with both pedals pressed can cause sufficient voltage sag (delta/imbalance from the rest) in one or more of those specific cells to incorrectly (?) trigger their software.
I am certain that GM (well, any company with their heads on straight) would not allow the accelerator to work, with the brake applied. This is about as basic as "smart" cars get. For an EV there would be no possible value, unlike those 19th century fuel burners.
 

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So, they gave me the gm technical line to call. I called the ev concierge and they couldn't tell me anything. If this goes on I'm thinking of seeing if I could just trade up to a newer model. I tried calling the technical line but was on hold for too long and gave up.
 

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Perhaps out of habit to prevent from rolling back when stopped in traffic on a steep hill? City of San Francisco has plenty of these. If someone is stopped really close behind you and you're facing uphill at a stoplight...

For others, some people are two foot drivers w/automatics? Don't get me started on a thread on Teslamotorsclub on this where a few people actually advocated doing this. In the past, I'd seen non-Bolts where it seems like someone is riding their brakes or they have brake switch/electrical probs. Brake lights come on a lot or are even on as they're accelerating.

BTW, you can find some "TMC" threads on the above by Googling for site:teslamotorsclub.com two foot driving and site:teslamotorsclub.com left foot braking.
This is exactly what happened to me. I'm on "L" on a steep hill, light is red so im rolling back so I lightly pressed the accelerator. Next thing i know i get the "reduced propulsion warning" and the light turns on. Called on star and got the P0BBD code and was told to take it to the dealership.
 
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