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Discussion Starter · #1 · (Edited)
Has anyone else noticed a direct correlation between the 12v battery voltage and BECM glitching?
(I understand that BECM failures are likely different, but mine is very consistently related to the 12v rail voltage - maybe this post will help someone else. In any case, we may learn something)

I have been using my Dave Jones "121GW" bluetooth multimeter to graph voltages while driving.
Pretty much every glitch has been when the +12v rail drops below 12.6v, which seems to happen occasionally during daylight, when the 12v charger presumably lets the 12v battery "float".
I have found that running with the headlights ON causes the 12v charger to not let the battery float and thus prevents glitching.

So my current "workaround regime", while I wait for the part is:
  • Trickle charge the (new) 12v battery with -12 lead disconnected when not driving (leaving about 60% SOC on traction battery). (Note: leaving the 12v lead connected while on the battery maintainer seems to work, but why not give the BECM a rest?)
  • To drive, disconnect trickle charger, reconnect -12v lead.
  • Right after starting the car, I turn on headlights to keep 12 rail above about 13.7v.
  • During the drive, if it's long enough, I run in HOLD mode occasionally for a bit to keep the engine freshly lubed in case of RPMode.
  • I can only spend a short time at the destination before the -12v rail gets down in the range of glitching the BECM while it's parked.
  • I keep a GOOLOO boost-pack (that does 15v) onboard if I need to bring the 12v rail back up above 12.6v to "bootstrap" the BECM.

Also, I have noticed that, if I get stuck with the "Shift to Park" message with of 0mi or 1mi, I can press the brake-pedal and start again and it will go into Reduced Propulsion Mode, which will toss 15v at the 12v battery, giving it a nice charge. Then after a bit in RPMode, I can stop the car, get out, get back in and often the car will show miles again and drive fine with the lights on.

I found this out after getting my 2017 scheduled for BECM replacement, figuring I'd replace the 12v battery to see if it helped. At first, it seemed to have fixed it, but then once the battery was allowed to "float" below 12.6 volts, the BECM became glitchy. If the 12v rail gets low enough then the BECM cannot seem to supply the 12v charger, it leads to a chicken and egg problem of the BECM not being able to bootstrap itself because it needs more 12v rail but cannot tell the 12v charger to start. (this is my hypothesis anyway)

I know I'm risking being stranded, but so far this works, at least this gives me the chance to keep the car exercised rather than rotting while waiting for the BECM replacement.

Maybe this thread will help those who may experience BECM problems for the first time. If their failure is the same "mode" as mine, then this could help get them home or to the dealer.

NOTE: Disconnecting the -12v lead will clear BECM codes that your dealer will need to confirm the failure and set up warranty service. ADVICE: Make sure you can reproduce the problem to the dealer and get it scheduled before playing around.

I'd love to hear if anyone else has noticed the correlation between low 12v rail voltage and BECM failing.
 
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Discussion Starter · #3 ·

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I believe my 2017 Volt needs a new BECM based on the vehicle's behavior, but warranty is over. 12V battery too low to start car. For a while was able to start by charging new 12V battery with engine. Then this stopped working. Used AGM trickle charger on new battery with negative terminal disconnected. After battery was charged, checked for parasitic drain and found 8 amp drain with car off, doors closed and fob in the house away from the car. Left battery disconnected because was concerned car could catch fire. Could BECM internal short cause this? Should be a recall. Definite safety hazard. Everyone should report these BECM problems to the NHTSA. Phone 888-327-4236.
 

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Discussion Starter · #5 ·
I believe my 2017 Volt needs a new BECM based on the vehicle's behavior, but warranty is over. 12V battery too low to start car. For a while was able to start by charging new 12V battery with engine. Then this stopped working. Used AGM trickle charger on new battery with negative terminal disconnected. After battery was charged, checked for parasitic drain and found 8 amp drain with car off, doors closed and fob in the house away from the car. Left battery disconnected because was concerned car could catch fire. Could BECM internal short cause this? Should be a recall. Definite safety hazard. Everyone should report these BECM problems to the NHTSA. Phone 888-327-4236.
Your BECM should be covered under the Voltec warranty. (8yr 100K miles). Are you over 100K
 

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I think it screws with the data stream
 

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Something to consider: a Volt tech on one of the other BECM threads has taken apart some of the replaced, bad BECMs . He found cold solder joints on the main chip in them. So...bad electrical connections that eventually failed. Wouldn't it be easy to imagine those poor contacts becoming intermittently bad and, therefore, sensitive to low voltage?
 
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Yes. You would need a higher voltage to jump across the cold solder joints.

The parasitic drain on the 12 volt battery has now dropped to 7 amps since the car has been sitting awhile. Called the closest Chevrolet dealer and asked if they had any BECM's in stock, and they said "no" but they had ordered two of them. The price of the part is $543.30. I'm sure the labor to remove the high voltage battery is extremely expensive.
 

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Something to consider: a Volt tech on one of the other BECM threads has taken apart some of the replaced, bad BECMs . He found cold solder joints on the main chip in them. So...bad electrical connections that eventually failed. Wouldn't it be easy to imagine those poor contacts becoming intermittently bad and, therefore, sensitive to low voltage?
if that was the case, makes me wonder why they didnt resolder the bad connections and stuff it back in, if its that hard to get them
 

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Also, the chips could be bad too. It's too hard to test those things at a dealership. They don't have high-tech electronic equipment to test chips or boards. At least I've never heard of it. Maybe they should start investing in that stuff. 😀
 

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Also, the chips could be bad too. It's too hard to test those things at a dealership. They don't have high-tech electronic equipment to test chips or boards. At least I've never heard of it. Maybe they should start investing in that stuff. 😀
could send them back to supplier and have them do it on exchange
my question would be why a cold solder joint, usually thats either from bad solder, that i have a hard time believing, maybe covid had something with supply. the other reason would be a high heat cool situation and i find that hard to believe in a temperatured controlled battery box . you could say that with the car shut off the temps of the box could go high in southern states, mine went bad in canada it it doesnt get hot here , so no, or maybe the chip itself generated the heat, becouse it wasnt working properly, that i would beleive. why wasnt it working properly, see post2 :)
 

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It is my understanding that cold solder joints happen during manufacture. I've actually done some soldering and it's tricky to do it correctly. I would assume the components are made by robots and something could have gone wrong with the solder flow, who knows what happened.
 

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It is my understanding that cold solder joints happen during manufacture. I've actually done some soldering and it's tricky to do it correctly. I would assume the components are made by robots and something could have gone wrong with the solder flow, who knows what happened.
sounds more like a gm engineer or someones speculation.
my response to that, if that was the case, then you would think, you would have failures right from the get go, not 2 or 3 years after the manufacture or 50k miles down the road. there is one other reason for failed solder joints that fits this profile that I have seen, that I have not said.
listen, this conversation is already making me nervous. so now i have to make a disclaimer
all of my thoughts past or going forward are purely speculation and in no way, either right or wrong , only my ideas with my limited knowledge looking from the outside in. and if anyone is wondering why i just said this i will give you a for instance. what if something i post leads to another reason why the bolts batteries fail and lg chem can come back against gm, billion of dollars, something i dont want to be part of. i just want a vehicle that works. sometimes its best to leave sleeping dogs lie.
post 2 has a solution for gm. me, if they dont address this, I will just throw another cap on my next vehicle and call it a day,
 

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what if something i post leads to another reason why the bolts batteries fail and lg chem can come back against gm, billion of dollars, something i dont want to be part of.
Ah, assuming the above is not a joke, you will have determined the true cause of the Bolt battery problem. The premise is the issues GM and LG identified had nothing to do with the true cause and they wasted a billions by not addressing the true cause. And by not telling anyone what the true cause of the fires is, you are helping Bolt owners, and GM. You are simply waiting for the new Bolt batteries to destroy some more cars or perhaps injure someone before letting the world in on your secret? Seems like a weird position to take. On the other hand, I'm assuming that GM and LG engineers are not complete idiots and they actually did find and fix the battery issue.
 

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I saw on this forum that there were BECM failures at all different mileages and even on brand new cars. My vehicle failed after the warranty was over, but apparently they can fail at any time. My opinions are also speculation. I really have no idea what is really going wrong with these cars, both Bolts and Volts. I hope they figure it out soon before they make more, in my opinion, defective cars. By the way, I'm not an engineer. I'm a retired welfare worker. Fortunately, I have old cars that still run! 😃
 

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I really have no idea what is really going wrong with these cars, both Bolts and Volts. I hope they figure it out soon before they make more, in my opinion, defective cars. By the way, I'm not an engineer. I'm a retired welfare worker. Fortunately, I have old cars that still run! 😃
What do you think is going on with the Bolts?

I have one, had no issues before the battery was replaced under the recall, have none now after. In fact, the car is better than it was. I now have 29 more miles of range and a brand new 8 year battery warranty on my 5 year old car. I'm extremely happy (LG, probably not so much).
 

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A Tesla model 3 caught fire in my neighborhood about a week ago, and, although there are different reasons why EV batteries catch fire, I just read this article and posted the link above which gives the most likely reason. Hopefully you're improved Bolt battery will be safer than the original.
 
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