Not your average charging problem
11-17-2014, 07:29 PM
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Not your average charging problem Hello all. I’ve got a problem with the charging system in my Silverado (2012, 6.2L (L9H)), and with the high level of technical expertise around here, I’m hoping someone can help me out.
Here’s the deal: The truck is in a constant state of overcharging. At startup, the voltage peaks at around 15.1-15.4v, then gradually works down to around 14.6-14.7v. It happens even on hot days, which puts it well into the gassing range for the batteries. No codes are thrown. There are many conditions that can cause the BCM to request higher voltage; In this case it seems to be the result of the BCM constantly believing the battery to be at only a 70% state-of-charge.
Prior to establishing that the BCM always calculated 70% SOC, either myself or the local GM dealer tried:
- Check all grounds & charge-related wires for resistance/breakage
- Check battery (tested good), tried new battery
- Check alternator (tested good), tried new alternator
- New Current Sensor
Nothing had any affect. The GM tech soon discovered that the BCM seems to be seeing 70% SOC no matter what.
Now here’s my dilemma; when the local techs were unable to solve the problem, they contacted GM’s remote support techs. After a point, the remote tech said that they couldn’t really go any further without pulling out the aftermarket wiring. The truck has aftermarket wiring which I did myself. It was all in place about 2 years ago, while this problem just popped up this past August. The wiring is cleanly and properly done though, so after showing the local tech what it was and how to simply disconnect it all, he agreed—off the record—that it was not part of the issue. He also—off the record—agrees with me that the logical next step seems to be to replace the BCM.
However, it seems once you contact remote support they get to determine warranty status; if they say the way to validate it as a warranty issue is to pull the wiring and establish a GM problem, then apparently that’s that. Remote support seems resistive to blaming the BCM, as apparently bad BCMs are unusual.
I, of course, absolutely do not want all my wiring pulled (Aux battery, lighting, audio), especially since I’m quite sure it’s not the problem, and in any case it can be disconnected without removing (and was during the dealer's inspections). I’m thinking of proposing the following: The dealer replaces the BCM. If it’s fixed, then it was a warranty issue and I should not be charged. If it’s not fixed, then I’ll at least pay for labor, maybe for the 2nd BCM also. I know the aftermarket wiring puts the dealer in a tough spot, but it seems a fair proposal.
Before going this potentially expensive route, I’m wanting to see if anyone has come across this before or can help identify the issue? I could find no other instance of this on the internet. Is there some other component that can affect perceived state-of-charge? One possible consideration is that the problem started shortly after pulling a trailer about 400 miles. I know Tow/haul mode activates charging mode, so I don’t know if this may have anything to do with it.
Well, this got long-winded. Sorry. Thanks for any input!
Here’s the deal: The truck is in a constant state of overcharging. At startup, the voltage peaks at around 15.1-15.4v, then gradually works down to around 14.6-14.7v. It happens even on hot days, which puts it well into the gassing range for the batteries. No codes are thrown. There are many conditions that can cause the BCM to request higher voltage; In this case it seems to be the result of the BCM constantly believing the battery to be at only a 70% state-of-charge.
Prior to establishing that the BCM always calculated 70% SOC, either myself or the local GM dealer tried:
- Check all grounds & charge-related wires for resistance/breakage
- Check battery (tested good), tried new battery
- Check alternator (tested good), tried new alternator
- New Current Sensor
Nothing had any affect. The GM tech soon discovered that the BCM seems to be seeing 70% SOC no matter what.
Now here’s my dilemma; when the local techs were unable to solve the problem, they contacted GM’s remote support techs. After a point, the remote tech said that they couldn’t really go any further without pulling out the aftermarket wiring. The truck has aftermarket wiring which I did myself. It was all in place about 2 years ago, while this problem just popped up this past August. The wiring is cleanly and properly done though, so after showing the local tech what it was and how to simply disconnect it all, he agreed—off the record—that it was not part of the issue. He also—off the record—agrees with me that the logical next step seems to be to replace the BCM.
However, it seems once you contact remote support they get to determine warranty status; if they say the way to validate it as a warranty issue is to pull the wiring and establish a GM problem, then apparently that’s that. Remote support seems resistive to blaming the BCM, as apparently bad BCMs are unusual.
I, of course, absolutely do not want all my wiring pulled (Aux battery, lighting, audio), especially since I’m quite sure it’s not the problem, and in any case it can be disconnected without removing (and was during the dealer's inspections). I’m thinking of proposing the following: The dealer replaces the BCM. If it’s fixed, then it was a warranty issue and I should not be charged. If it’s not fixed, then I’ll at least pay for labor, maybe for the 2nd BCM also. I know the aftermarket wiring puts the dealer in a tough spot, but it seems a fair proposal.
Before going this potentially expensive route, I’m wanting to see if anyone has come across this before or can help identify the issue? I could find no other instance of this on the internet. Is there some other component that can affect perceived state-of-charge? One possible consideration is that the problem started shortly after pulling a trailer about 400 miles. I know Tow/haul mode activates charging mode, so I don’t know if this may have anything to do with it.
Well, this got long-winded. Sorry. Thanks for any input!
11-20-2014, 09:17 AM
#3
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Any chance you could find a junkyard with a wrecked truck like yours ans throw it in just to see if it fixes that problem? Im sure with vehicles getting more and more advanced such as your 2012 you wont be able to find the exact bcm you need but if you find a wrecked truck with one just swap it and check voltage. Unless the airbags are deployed, i csnt remember if the bcm has anything to do with airbags but you dont want to replace those either. Either that or have gm put in a new bcm sounds like a logical next step.
12-10-2014, 04:59 PM
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Well, I didn't want to put in an incorrect BCM and potentially cause more issues. So, I paid the dealership to swap in and program a new one. No effect. 
Anybody who has a brilliant idea on next steps would be my new favorite person.
Anybody who has a brilliant idea on next steps would be my new favorite person.