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Discussion Starter #1
Hello, I haven't posted in a while but I have a new problem with my 2011 Volt #1819.

When the car is turned off, plugged in, and charging the 12V battery is not being charged. Instead it is discharging. However when I turn the car on and drive the 12V is being charged. I checked the voltage at the 12V battery with my trusted Fluke Multimeter. Before plugging in the voltage is about 12.4 V. When I plug the car in, the voltage is still 12.4 Volts. Soon I hear fans and pumps running, and the voltage slowly drops, 12.35....12.30....etc. At the end of a full charge the voltage at the 12V battery is about 11.8 (ish)

I also noticed when I drive the next morning and monitor the 12V, the charging volts stays around 13.9 volts for up to an hour. Only after driving longer than an hour will the volts drop to 12.5 (energy saving mode)

I experimented by attaching my Battery Tender 5 Amp trickle charger to the 12V battery and running it all night. The battery tender fully charged my 12V. While driving to work the following morning, the 12V charging went into 12.5V energy saving mode within less then 10 minutes from turning the car on, like it should.

I decided to track down the problem. I removed the inner wheel plastic bodywork and gained access to the Lear onboard battery charger in the front right corner behind the front bumper. With the car off and not plugged in, I disconnected the two pin connector for charging the 12V battery. I measured voltage across the two pins on the chassis side of the connector, it measured 12.5 volts, exactly the same measurement across the 12V battery posts. with that connector disconnected I plugged the car in. No charging (orange light). Next I unplugged car. Turned car on, and check engine light on. Fault code U1838. Cleared code. The on board charger obviously checks for battery voltage across the two pins and disables charging when it doesn't see the battery. Next I plugged in the charging connector and then plugged in the charge cord. I back probed the connector, voltage across pins 12.5V. I disconnected the connect WHILE the charge cord was plugged in and voltage across pins on charger side of connector was 13.5V. Voltage across pins on chassis side of connector 12.5V. Next I back probed the pins on the back side of the charger connector and watched voltage while I plugged in the connector. 13.5V disconnected, 12.5V connector. Next I pierced the insulation on the charge wires right where they break out of the on board charger. Same measurements...13.5V with connector discounted and 12.5V connected. This tells me at the wiring between the on board charger and the 12V battery is working correctly, and the problem is inside of the Lear on board charger. I also want to point out that with the exception of me disconnecting the 12V charge connector and plugged in the charge cord, no DTCs are being set and the check engine light never comes on.

I want to remove the Lear on board charger, open it, and inspect for visible signs of a damaged component. I understand there may be high voltage risks involved as capacitors may store high voltage for long periods of time. If I was to remove the high voltage cables from the Lear on board charger then re-attach the cables will the Volt function correctly, or is there a risk by doing this it may disable something on the car and need to be reset by the dealership? The price for a new Lear on board charger is about $950, and I have found used units between $250 to $500. If I replace the on board charger with another unit, is there a risk of the car not working correctly until the dealership resets something with their computer?

Also my 2011 Volt has 102,000 miles. I assume this problem is not covered by the warranty. Is there even a remote possibility that a dealership may repair this under warranty? I want to stress that the Volt does charge it's high voltage battery perfectly well, the problem is just limited to charging the 12V battery while plugged in.

Sorry for the long post. I'm hoping to fix my poor old Volt.

-Eric
 

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Discussion Starter #3
I forgot to mention. I replaced the 12v battery about a month ago with a genuine ACDelco AGM.
 

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My GUESS is a part is a part in this case and replacing the charger with another will not cause issues on the next startup. But it's just a guess. If the car is off, how would it know the part was replaced as long as the new unit functions? It seems the worst case is you are out $250 and a tow to the dealer.
 

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Does the battery drain enough that you need to jump start the car?

My recommendation is always start with the simple things when diagnosing a problem. I would have a battery shop test your AGM 12v battery with a digital microprocessor type tester (my local shop has one that looks like credit card POS with printer built in). This device will also test your car's charging system.

If it points to the DC-DC Converter you can then start trouble shooting there.
 

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On 2011/2012, the OBCM does not charge the 12V. The 12V is only charged during driving, as designed. There WAS a change in this behavior for 2013+, so that at the END of the traction battery charge cycle, the 12V battery will be "topped" off, and "maintained". But the 12V battery only gets a full charge during driving.

Search for one of WOTs posts on this. I don't think you have a problem. And 12.5V on the AGM is fine. I see 12.5 to 12.2V on mine.
 

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On 2011/2012, the OBCM does not charge the 12V. The 12V is only charged during driving, as designed. There WAS a change in this behavior for 2013+, so that at the END of the traction battery charge cycle, the 12V battery will be "topped" off, and "maintained". But the 12V battery only gets a full charge during driving.

Search for one of WOTs posts on this. I don't think you have a problem. And 12.5V on the AGM is fine. I see 12.5 to 12.2V on mine.
Normally the DC-DC converter only supplies power when Volt is ON (2012 model). However, there are some scenarios where 12V power is supplied when EVSE is plugged and vehicle is being charged, to move pumps, fans, etc... for conditioning the battery.

You can rule out the the DC-DC converter by measuring battery voltage when car is OFF (not plugged in). Wait for voltage to stabilize before measuring voltage. After a few minutes turn vehicle ON, but keep all accessories off (AC, headlamps, radio, etc...), the voltage should be at least 1V greater than reading when car was OFF.

Also take note that the Charging System has 6 modes of operation, each with its own voltage. So just because the charging system isn't behaving like a regular car, doesn't mean its broken.
1 Sulfation mode
2 Normal mode
3 Fuel economy mode
4 Headlamp mode
5 Voltage reduction mode
6 Plant assembly mode

You don't mention any warnings, indicators or lights on the dash, the car will tell you if there's a problem with the DC-DC converter.

Finally, take note that a battery needs to be at rest for at least 24 hours to take a voltage reading to determine accurate state of charge. This is necessary for the acid in the cells to equalize. You also need to take into account ambient temperature, Service Manual includes a table for different SOC readings at different temperatures.
 

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Each component has it's own ID, and if you replace any component with a different one, the system will not function until a dealer re-configures it.
 

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Some of this you can see and watch with a 12 Volt power port digital voltmeter

You may even catch the 14-15 Volts bus readings while driving and you get to see only battery for a few mins after shutting down.

AND after car is off before opening the door -- watch the voltage when you using the parking break.
 

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Did you check for a blown 40amp fuse (#44) located in the underhood fuse block?

That is the fuse that collects the 12V charging output from the Lear On-Board Charging Module (on the X2 2-wire connector) and fuses it as it passes back to the 12V AGM.

So from the underhood fuseblock it passes up to and through (unfused) the auxillary underhood fuseblock (the underhood boost point junction) then all the way to the back of the car to the 150A mega fuse ontop of the 12V battery.

If that fuse (U44UA) was blown you would have A "No Charging" condition while plugged in and actively charging, yet OK charging from the APM (DC DC Converter) is fine when the car is ON.

HTH
WOT
 

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Discussion Starter #11
My GUESS is a part is a part in this case and replacing the charger with another will not cause issues on the next startup. But it's just a guess. If the car is off, how would it know the part was replaced as long as the new unit functions? It seems the worst case is you are out $250 and a tow to the dealer.
The Lear on board charger communicates with the rest of the car with using a CANBUS network. The on board charger could broadcast its unique serial number and the car could reject if a different serial number appeared on the network.
 

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Discussion Starter #12
Does the battery drain enough that you need to jump start the car?

My recommendation is always start with the simple things when diagnosing a problem. I would have a battery shop test your AGM 12v battery with a digital microprocessor type tester (my local shop has one that looks like credit card POS with printer built in). This device will also test your car's charging system.

If it points to the DC-DC Converter you can then start trouble shooting there.

Even though the 12v battery becomes partially discharged after a full charging session, there is still enough energy in the 12v battery for my Volt to power on in the morning. My Volt has actually never left me stranded with a dead 12v battery but I keep jumper cables in the hatch just in case
 

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Discussion Starter #13
On 2011/2012, the OBCM does not charge the 12V. The 12V is only charged during driving, as designed. There WAS a change in this behavior for 2013+, so that at the END of the traction battery charge cycle, the 12V battery will be "topped" off, and "maintained". But the 12V battery only gets a full charge during driving.

Search for one of WOTs posts on this. I don't think you have a problem. And 12.5V on the AGM is fine. I see 12.5 to 12.2V on mine.
With all due respect I believe that is wrong. It's my understanding that while the Volt is actively charging the HV battery (solid green dash light), it is also charging/topping off the 12v battery too. This is necessary because there are many fans, pumps, and electronic control units that draw power from the 12v system while the HV battery is charging.

It's also my understanding that for the Gen1 Volt, it's the Lear on board charger that supplies this 12v charging to the 12v battery. For the Gen2 Volt, the DC-DC converter supplies energy to the 12v while charging the HV battery.

I believe the change that GM made with 2013+ models is in regards to what happens AFTER the HV battery is fully charged. In older Volts, when the HV battery is fully charged, the 12v battery never gets topped off. In the later Gen1 Volts, the car will periodically top off the 12v battery as long as the car is plugged in and the HV battery is fully charged.
 

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Discussion Starter #14
Normally the DC-DC converter only supplies power when Volt is ON (2012 model). However, there are some scenarios where 12V power is supplied when EVSE is plugged and vehicle is being charged, to move pumps, fans, etc... for conditioning the battery.

You can rule out the the DC-DC converter by measuring battery voltage when car is OFF (not plugged in). Wait for voltage to stabilize before measuring voltage. After a few minutes turn vehicle ON, but keep all accessories off (AC, headlamps, radio, etc...), the voltage should be at least 1V greater than reading when car was OFF.

Also take note that the Charging System has 6 modes of operation, each with its own voltage. So just because the charging system isn't behaving like a regular car, doesn't mean its broken.
1 Sulfation mode
2 Normal mode
3 Fuel economy mode
4 Headlamp mode
5 Voltage reduction mode
6 Plant assembly mode

You don't mention any warnings, indicators or lights on the dash, the car will tell you if there's a problem with the DC-DC converter.

Finally, take note that a battery needs to be at rest for at least 24 hours to take a voltage reading to determine accurate state of charge. This is necessary for the acid in the cells to equalize. You also need to take into account ambient temperature, Service Manual includes a table for different SOC readings at different temperatures.
My DC-DC converter is working correctly. The 12V is being charged while the car is ON. However it takes almost an hour after turning on for the DC-DC CHARGER to transition from #2 Normal Mode to #3 fuel economy mode. This is because the 12v battery is always partially discharged over night so in the morning the DC-DC converter needs to replenish the 12v battery with a large amount of energy which takes considerable amount of time. If I put my trickle charger on the 12v battery over night, then it takes less then 10 minutes of driving for the car to enter #3 fuel economy mode.
 

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Did you check for a blown 40amp fuse (#44) located in the underhood fuse block?

That is the fuse that collects the 12V charging output from the Lear On-Board Charging Module (on the X2 2-wire connector) and fuses it as it passes back to the 12V AGM.

So from the underhood fuseblock it passes up to and through (unfused) the auxillary underhood fuseblock (the underhood boost point junction) then all the way to the back of the car to the 150A mega fuse ontop of the 12V battery.

If that fuse (U44UA) was blown you would have A "No Charging" condition while plugged in and actively charging, yet OK charging from the APM (DC DC Converter) is fine when the car is ON.

HTH
WOT
I checked all the high amp fuses in the engine compartment fuse box. However I'll check #44 again to make sure I didn't miss it. If the fuse was blown, I think the Car would not charge the HV battery when plugged in (orange dash light) and would set a DTM (U1838)
Because the Lear on board charger needs to see 12v battery voltage before HV charger starts
 

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My DC-DC converter is working correctly. The 12V is being charged while the car is ON. However it takes almost an hour after turning on for the DC-DC CHARGER to transition from #2 Normal Mode to #3 fuel economy mode. This is because the 12v battery is always partially discharged over night so in the morning the DC-DC converter needs to replenish the 12v battery with a large amount of energy which takes considerable amount of time. If I put my trickle charger on the 12v battery over night, then it takes less then 10 minutes of driving for the car to enter #3 fuel economy mode.
Does this battery drain only occur while the car is being charged or does it also happen when car is OFF and not plugged in? Since the car needs 12V when charging to control High Voltage Battery temperature this can narrow things for you.

If it also happens while OFF and not charging, you might need to perform a battery electrical drain/parasitic load test. Start with disconnecting aftermarket accessories.
 

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Discussion Starter #17
Does this battery drain only occur while the car is being charged or does it also happen when car is OFF and not plugged in? Since the car needs 12V when charging to control High Voltage Battery temperature this can narrow things for you.

If it also happens while OFF and not charging, you might need to perform a battery electrical drain/parasitic load test. Start with disconnecting aftermarket accessories.
The Drain only happens when the car is OFF, plugged in, and activity charging (solid green dash light).


I can go weeks with the car plugged in the garage, or weeks with the car sitting in a parking lot not plugged in and the 12V is not drained. It will power on just fine. The drain only happens the 3.5 hours (Level 2) or 9-10 hours (level 1) when plugged in and charging.
 

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Discussion Starter #18
Last night I did not plug in my trickle charger to the Volt's 12v battery because I was using it on another vehicle with a dead battery....LOL

This morning the Volt powered on fine as it normally does. However while driving the 12v charging mode stayed in the normal mode for 45 minutes at 13.9 to 14.0 volts. This whole time it was putting energy back in the 12v battery. After 45 minutes of driving the charging mode transitioned to fuel economy mode at 12.5v. When I attach my trickle charger to the 12v battery over night, the next morning it takes less than 10 minutes (usually less than 5) to enter fuel economy mode at 12.5. I believe if I fix my car (or keep plugging in my trickle charger) I will get better AER range than if I don't. This is why I am looking for a solution. I am considering getting second trickle charger and permanently installing it in my Volt and just plugging it in every night (in addition to the EVSE) as an alternative to paying $950 for a new on board charger
 

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@Eric99
Still following you on this. My 2014 did leave me with a completely dead 12V battery once after 12 days sitting in my garage unplugged, so I have also done some similar testing. 13.0V from the OBCM doesn't seem like much to recharge the AGM during traction battery charge. I've also seen considerable time on mine, going from the "2 normal" charge mode to the "3-economy" mode, by watching a meter plugged into the top of dash 12V outlet, while driving But my normal commute is only 15 minutes, so hard to tell. And like you, I've also used a float charge maintainer on the AGM, to see if I get longer all electric range, but with the short commute (8 miles), and other variations, inconclusive. But I've actually installed a small jack in the back hatch fuse box area to let me easily plug in either a small solar panel, or a float charger.

My thinking had moved to the passive keyfob signaling, if the keyfob is too close, may (?) it cause the AGM to discharge due to the car's receiver constantly running(?) In my dead battery case, I think the keyfob was left less than 15 ft from the car (for 10 days). Since then (and given key fob repeater spoofing), I always place my fobs in an old cookie tin. Still have the original AGM battery, so far so good.
 

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The Lear on board charger communicates with the rest of the car with using a CANBUS network. The on board charger could broadcast its unique serial number and the car could reject if a different serial number appeared on the network.
Thanks for the cautionary detail, Eric99! To be clear, it "could" broadcast the SN, but does anyone know that it does?
 
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