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Discussion Starter #1 (Edited)
So, this is extremely disappointing, but it looks like our Volt is experiencing brake failures similar to those described in threads such as:

http://gm-volt.com/forum/showthread.php?249490-2013-Chevy-Volt-Brake-Failure

Our story in a nutshell is as follows. My wife and I were hoping to make a change late last year -- reduce costs, limit carbon emissions, yada yada. I did a bunch of research, including regression analysis on pricing, and ultimately settled on buying two used Volts. We bought my wife's 2013 red Volt with just over 30K miles and a clean CarFax report (off lease, nothing but maintenance) in late April. We bought a second new old stock 2014 a few weeks later.

Everything was great until right around June 28th. My wife reported that she had been driving along when suddenly the car felt "weird" and the check engine light came on, but then she continued to drive home. I scanned the codes and saw U0129, which appeared to be related to the main computer no longer being able to communicate with the brake controller. I mentioned this to my wife, to which she replied "oh yeah, I didn't have brakes and it felt like I was driving on ice". Hmmm. I tried to convince her to bring it in, but she wanted to continue to drive it instead so I went along.

Fast forward to July 13th. My wife stopped at our day care provider to pick up our kids. When she came back out and started the car it lit up like a Christmas tree. She no longer had power steering or power brakes. She didn't think she could stop, but the tow driver who ended up being called noted that the mechanical brake did work if you jammed the pedal down. We towed the car to a dealership (yay AAA), who then proceeded to work on it for the better part of a week.

The dealer reported they were in repeated contact with the GM Volt team trying to diagnose the problem. From my understanding the OBD codes (I hadn't scanned them this time) indicated failures to communicate with multiple subsystems. Our contact at the dealer explained that the various controllers were wired in series, with brakes at or near the front, so if they went out all of the other systems would also go out. However, for some reason they were not able to determine if it was a hardware or software failure (not reassuring!), so at the request of GM they updated the software for nearly every or all controllers. The specific updates were as follows:

EBCM # 28A43
ECM #11AA6
HP2 # CBAA2
BCM #519E3
BECM #CAFA2
STEERING # 31443

I asked if any of these addressed this particular problem, to which the dealer reported they did not (not reassuring!). They had however "fixed the problem" in that in doing so the car was again able to be driven. We were a bit skeptical, but willing to go with it being a software issue as it should be easy to diagnose if it was a hardware failure.

Everything was great until again today when my wife stopped on her way home from work to pick up the kids. Again she went in and when she came out to drive them home the car lit up with all sorts of warnings. However, this time it did reset again after restarting the car, so I drove over and we had the harrowing experience of me leading her in my Volt just in case the brakes went out again. Not remotely reassuring. I've scanned the car and again we have U0129, as well as C0700 and 3-5 other "unknown" faults.

Again, this is extremely, extremely disappointing. We were so proud of our Volts. I haven't used gas on my commute since I got the car, and my wife won't once her job changes at the end of the month. Now I'm questioning whether or not the cars are even safe as this has happened to other owners and GM seems unable to diagnose the problem. We're now likely facing a $1500 brake controller replacement for a car that now has only 34k miles and even worse gives me little confidence that it will actually solve the problem.

I've been trying half-heatedly to evangelize the car as I do believe it's direction we need to and should go for economic and environmental reasons, but I have had to tell my friends "we love our Volts, but...." which I think has dissuaded some of them from even considering the vehicle. It's a shame that GM could get so much right with this car, but get one critical thing so very wrong.

:(
 

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What exact device are you using to scan for codes?

Is it staying connected at all times?

FYI the U-codes you are experiencing are first of all ARE NOT common to some of the other brake threads, (other than ALL brake issues result int he identical warning lights but...)

These specific U-codes are quite rare actually. but often artifacts of CAN communications that are interrupted for some reason. (Possibly due to some DLC connected device?)

Otherwise it's a network issue that really has nothing to do with the brakes per se, and what the dealership did (updating all the various primary control modules) is spot on.

Did you TELL the dealership you used some sort of code reader on the car??

Ultimately until we hear exactly which DTCs are present now we can't be much help. Partial lists are useless as it is the exact combination of U-codes that is issued to isolate potential areas of fault in a network that includes over 200 feet of wire.

Get back with ALL of the U-codes and more importantly in WHICH modules they have been set (preferably from the dealership and not some unapproved device) and perhaps we can provide some guidance

Welcome to gm-volt.com

WopOnTour
 

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12 Volt Battery? Appt of strange things have happened when the 12V battery has failed.
I've seen this kind of suggestion before, but obviously the 12V battery hasn't failed, because they could start the car. If the brakes go out when the 12V battery is marginally low, then the Volt isn't safe for public roads. I don't think it's the 12V battery. Still, when the computer network inside the car is so complicated that life safety system failures can't be diagnosed, it's a serious problem.
 

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It's a shame that GM could get so much right with this car, but get one critical thing so very wrong.

:(
I can understand your frustration. If it makes you feel any better, there are a few isolated incidents of this happening on the Prius too. This is more of a "modern hybrid brakes are complicated" issue and less of a "crappy design" issue.

I am inclined to agree with WopOnTour. Because the problem presents intermittently, this seems like a communication issue and not a hardware issue. It could be something as simple as a lose or corded connection. Have you made any electrical modifications? In some cases, installing aftermarket HID headlights or using universal CAN BUS scanners can interrupt critical network communications leading to cascading system failures.
 

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I second the 12V battery (possible) problem. It may be as simple as a loose connection. The typical symptom is exactly what you describe (happened to me), wherein all sub-systems start to fail, and the dash board lits up. Definitely worth making sure that is not the issue.
 

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Discussion Starter #7
Thanks for the feedback folks. I really appreciate it.

What exact device are you using to scan for codes?

Is it staying connected at all times?

FYI the U-codes you are experiencing are first of all ARE NOT common to some of the other brake threads, (other than ALL brake issues result int he identical warning lights but...)

These specific U-codes are quite rare actually. but often artifacts of CAN communications that are interrupted for some reason. (Possibly due to some DLC connected device?)

Otherwise it's a network issue that really has nothing to do with the brakes per se, and what the dealership did (updating all the various primary control modules) is spot on.

Did you TELL the dealership you used some sort of code reader on the car??

Ultimately until we hear exactly which DTCs are present now we can't be much help. Partial lists are useless as it is the exact combination of U-codes that is issued to isolate potential areas of fault in a network that includes over 200 feet of wire.

Get back with ALL of the U-codes and more importantly in WHICH modules they have been set (preferably from the dealership and not some unapproved device) and perhaps we can provide some guidance

Welcome to gm-volt.com

WopOnTour
I did tell the dealership that I had scanned the codes the first time. Again, the second time I did not scan them at all. Car went right up on the tow truck and straight to the dealer. I'll try to get the full set of codes from the first trip tomorrow, or when they scan them again this time. Nothing was indicated on the first invoice.

Also, the device is:

https://www.amazon.com/dp/B001LHVOVK/ref=pe_385040_30332200_pe_309540_26725410_item

It is definitely not connected unless there is an issue.

Still, when the computer network inside the car is so complicated that life safety system failures can't be diagnosed, it's a serious problem.
Yup, I agree 100%. :(

I second the 12V battery (possible) problem. It may be as simple as a loose connection. The typical symptom is exactly what you describe (happened to me), wherein all sub-systems start to fail, and the dash board lits up. Definitely worth making sure that is not the issue.
OK, this is interesting. I'll definitely mention it tomorrow. I also should have mentioned that the two times it happened at day care were after my wife had driven ~25 miles to pick up the kids on very hot days. Not sure if that's relevant, like maybe the heat is causing havoc on a battery that's starting to go? Not sure if it was checked last time.
 

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Discussion Starter #8
I can understand your frustration. If it makes you feel any better, there are a few isolated incidents of this happening on the Prius too. This is more of a "modern hybrid brakes are complicated" issue and less of a "crappy design" issue.

I am inclined to agree with WopOnTour. Because the problem presents intermittently, this seems like a communication issue and not a hardware issue. It could be something as simple as a lose or corded connection. Have you made any electrical modifications? In some cases, installing aftermarket HID headlights or using universal CAN BUS scanners can interrupt critical network communications leading to cascading system failures.
Missed the second part of this. Again, nope nothing done by us and as far as I can tell the car is stock. I have no idea whether or not connections were tested and at least re-seated, but you'd like to hope it would be. And again, the more alarming fact is that this can happen and it appears to be incredibly difficult to diagnose.
 

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Still, when the computer network inside the car is so complicated that life safety system failures can't be diagnosed, it's a serious problem.
Missed the second part of this. Again, nope nothing done by us and as far as I can tell the car is stock. I have no idea whether or not connections were tested and at least re-seated, but you'd like to hope it would be. And again, the more alarming fact is that this can happen and it appears to be incredibly difficult to diagnose.
Well you really need to keep in mind that the Volt is essentially no different than just about any other modern car or truck on the roadways today. ALL rely heavily on advanced multiplexed network communications, operating across dozens of modules and resting on hundreds of feet of wire (mostly twisted pair, but some single wire networks and even fibre-optic - although not on the Volt)

So what makes this type of diagnosis interesting is the DTCs (of the "U" variety) are actually set in modules THAT HAVE NO ISSUE. In other words Modules A, B, and C may actually set the exact same U-code, indicating Module D "wasn't home" for some reason. When this type of situation occurs intermittently it can be some of the most difficult diagnosis that exists in the modern automobile.

Fortunately General Motors has been training it's technicians for many years on multiplexed architecture and the various techniques necessary to isolate the faults present in ANY network. From multiple speed and node GMLAN/CAN, MOST, and LIN bus networks to the more simple UART and SPI hard-wired interfaces these techs have seen and worked with all of them for many years.

So it's important to state that there really isn't ANYTHING all that different about this type of network diagnosis on the Volt than for any other 2011-16 GM. All use a common network topology in a layered format. But it's basic wiring 101.

So the first point of business Is recording WHICH U-codes are being set in WHICH modules and over-laying that knowledge over the network schematics and the network diagnostic documents.
A challenge yes, but something special because it's a Volt? Not so much...

WopOnTour

PS> This particular area of electrical diagnosis happens to be one in which I am particularly versed in, so providing you are able to get accurate and timely information from the dealership I may be able to be of some assistance. At the very leas helping you to understand what is going on in the service bay.

So again, this starts with an exact list of DTCs being reported from each specific module. Ask the technician for a printout or PDF copy of the " Vehicle Wide-Area DTC and ID Report"
 

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Note that the Volt has a mechanical brake backup called 4-wheel push through. So you shouldn't ever not have brakes available. You lost the "assist" which will may feel like you've lost your ability to brake, but it's still there.

I think WOT has said that you can experience how this works if you leave the car off for a few minutes and then try braking without turning the Volt back on. The pedal will travel easily but then firm up before you hit the bottom. Obviously this is hardly ideal but it's good to know about.
 

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Note that the Volt has a mechanical brake backup called 4-wheel push through. So you shouldn't ever not have brakes available. You lost the "assist" which will may feel like you've lost your ability to brake, but it's still there.

I think WOT has said that you can experience how this works if you leave the car off for a few minutes and then try braking without turning the Volt back on. The pedal will travel easily but then firm up before you hit the bottom. Obviously this is hardly ideal but it's good to know about.
This is true. It is essentially impossible to have "no brakes". In the event of an electrical issue (as this likely is) that affects the braking system, 4-wheel push though which is essentially un-assisted base brakes, becomes the default. However you WILL have to push the pedal though more travel than usual to obtain the desired effect.

IME most people that run into trouble with 4-wheel push through, often have their seat set too far back and get "straight-legged" during the stop (which means they cannot apply sufficient pressure and left with only foot flexion.
But as a general rule when adjusting your seat, you should always be able to place your right foot directly ON the firewall behind the brake pedal to insure adequate pressure can be applied should a loss of assist occur.
But that recommendation has essentially been the case since the advent of power brakes.

WOT
WOT
 

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Note that the Volt has a mechanical brake backup called 4-wheel push through. So you shouldn't ever not have brakes available. You lost the "assist" which will may feel like you've lost your ability to brake, but it's still there.

I think WOT has said that you can experience how this works if you leave the car off for a few minutes and then try braking without turning the Volt back on. The pedal will travel easily but then firm up before you hit the bottom. Obviously this is hardly ideal but it's good to know about.
I experienced the sinking feeling of no brakes before, when starting the car and shifting into drive too quickly before the brake booster could do its thing. I was in my garage, realized I parked too far back, pushed the on button while shifting to D followed by panic and then a sigh of relief that I narrowly avoided slamming my new car into my big tool box.
 

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I experienced the sinking feeling of no brakes before, when starting the car and shifting into drive too quickly before the brake booster could do its thing. I was in my garage, realized I parked too far back, pushed the on button while shifting to D followed by panic and then a sigh of relief that I narrowly avoided slamming my new car into my big tool box.
Yikes. Another reason why a little patience is a virtue. Glad you avoided the tool box. To WOTs point about the seat position, had a smaller person gotten into the car and skipped adjusting the seat, and then done what you did, the outcome might have been different.
 

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So when it is said the bus is connected serially, does that mean electrically isolated? so say a short in bus from A to B, may cause the signal to seem to fail between B and C but can be assumed that it is really a problem with the first LRU in the stream (from A to B, so either A or B or wires between are bad)? That a short say in the bus between B and C would not create a fault in the A to B path?

Is this like a IEEE bus? where each new connection is like spliced into an existing device?

suppose I could look this up....
 

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Well you really need to keep in mind that the Volt is essentially no different than just about any other modern car or truck on the roadways today. ALL rely heavily on advanced multiplexed network communications, operating across dozens of modules and resting on hundreds of feet of wire (mostly twisted pair, but some single wire networks and even fibre-optic - although not on the Volt)...
They don't have to be that modern. My daughter-in-law had a 1999 Chrysler Concorde that seemed possessed. The radio would randomly change stations and volume, the A/C would randomly turn on/off, and the fan speed would change on its own. Even the speedometer acted weird. After she had spent >$700 at a shop trying to get it fixed (they replaced the BCM, which didn't help), I did a little Google searching and found a guy that had fixed his identical car by replacing the TCM (transmission control module). I replaced her TCM with one I got from a junk yard, and that fixed the problem. Apparently, the TCM was putting noise on the bus, which was affecting the BCM.

So yes, cars are rolling computer networks, and have been for some time.
 

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Again, this is extremely, extremely disappointing. We were so proud of our Volts. I haven't used gas on my commute since I got the car, and my wife won't once her job changes at the end of the month. Now I'm questioning whether or not the cars are even safe as this has happened to other owners and GM seems unable to diagnose the problem. We're now likely facing a $1500 brake controller replacement for a car that now has only 34k miles and even worse gives me little confidence that it will actually solve the problem.

I've been trying half-heatedly to evangelize the car as I do believe it's direction we need to and should go for economic and environmental reasons, but I have had to tell my friends "we love our Volts, but...." which I think has dissuaded some of them from even considering the vehicle. It's a shame that GM could get so much right with this car, but get one critical thing so very wrong.

:(
(Bold text above) If the car is under 36k miles, you should still be under the bumper-to-bumper warranty, so you won't be out any money.

I understand this is scary and frustrating. But this kind of thing can (and does) happen to every model of car. Search forums for any other model and you'll see various weird things that happen to the unlucky few. I do understand the feeling of "can I trust this car after this?", but hopefully they'll find the root cause and you'll have many happy miles ahead of you. Keep us posted...
 

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(Bold text above) If the car is under 36k miles, you should still be under the bumper-to-bumper warranty, so you won't be out any money.

I understand this is scary and frustrating. But this kind of thing can (and does) happen to every model of car. Search forums for any other model and you'll see various weird things that happen to the unlucky few. I do understand the feeling of "can I trust this car after this?", but hopefully they'll find the root cause and you'll have many happy miles ahead of you. Keep us posted...
The issue is we're out of the 36 months, not the 36k miles.
 

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The issue is we're out of the 36 months, not the 36k miles.
Oops, my bad, I also have a 2013 so for some dumb reason I assume everyone bought theirs when I did and I still have another month or so of warranty :eek:
 

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They don't have to be that modern. My daughter-in-law had a 1999 Chrysler Concorde that seemed possessed. The radio would randomly change stations and volume, the A/C would randomly turn on/off, and the fan speed would change on its own. Even the speedometer acted weird. After she had spent >$700 at a shop trying to get it fixed (they replaced the BCM, which didn't help), I did a little Google searching and found a guy that had fixed his identical car by replacing the TCM (transmission control module). I replaced her TCM with one I got from a junk yard, and that fixed the problem. Apparently, the TCM was putting noise on the bus, which was affecting the BCM.

So yes, cars are rolling computer networks, and have been for some time.
Ok this seems to indicate one bad box can kill the whole bus. So, since so many systems are affected here, I would get a bus reader and look for crap on the line when it is in the act. Then try to disconnect one box at a time. Failing that sart to isolate the the bus between line replaceable units until the bus traffic looks ok.

Also, if the person picking of the kids is using the vehicle with known iffy brake condition.....maybe switch cars at least?
 
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