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Those are my instructions. I did end up flashing the BECM to make sure it was in sync with the updated HPCM2 code that I had flashed. Keep in mind that the BECM flash takes at least 15 minutes. Make sure your laptop has AC power, and just walk away for 30 minutes. Otherwise you’re going to think the flash failed and be tempted to do something bad before the process actually finishes.

*Disclaimer: Flashing a module always carries the risk of bricking it. Proceed at your own risk!
 

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I have seen this on a few cars, comes in for the message and the sensor showed a failure as history only. Replace the sensor and program the modules just to have the car come back with the same issue within 6 months. Called GM tech assit and they have no new ideas other then to replace the sensor and the connector for that sensor. Did the repair and a month later, same issue. This time I rewired the complete circuit from the Hybrid Powertrain Control Module 2 (hpcm2) to the sensor. New terminals in the hpcm2 connector, new wires from the hpcm2 to the new connector and sensor. All terminals were soldiered to the wires for the best connection possible. This bypassed one connector located under the hood so the new circuit is much better. After this
repair, I have not seen the car back for this issue, repaired over a year ago (knock on wood). The problem with this circuit is that its a very low amp circuit and its looking for a small voltage drop to set the code. So if there is just a small amount of resistance in the circuit, it can cause this issue. I have done this repair on 3 cars now, not one has come back, now any car with this issue that I get has this repair done.
If I understand this correctly, you are stating that the circuit for the coolant level or WOT sensor plug does not require resistance in order to send the proper signal to the hpcm2 and desires instead to see ideally, a dead short on that circuit throughout, correct? If that is the case, then the WOT defeat plug, or sensor rather, is really just a jumper plug that you could otherwise wire the leads together to short only without the $30-$40 price tag. I assumed that the WOT defeat plug was either a short jumper or at least included a resistor wired in series that the hpcm2 is/was expecting to see. I've defeated a few airbag codes by using resistors instead of deal with the expense of replacing the airbags on a wrecked Volt that I repaired a couple years ago.. Let me know if we are on the same page, much appreciated.
 

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Hi All,

It's been a while since March this year but I have a small update.

The SHVCS message came back on yesterday so I did some reprogramming. First I did the HPCM, which was already up to date, no change in the version of the firmware. That much was made clear by it showing warnings before letting a user reprogram the same version. I also noticed that the update notes for the HPCM mentioned a Gen1 isolation issue.

I then checked the BECM module in SPS and saw its update notes also mentioned this, so I updated the BECM as well. No warning appeared about flashing with the same version, which stands to reason because I didn't update the BECM back in March. I charged for about half an hour just to get enough km for a small test trip, and everything seemed fine. It has since been charging overnight and will be back in regular use as needed.

One thing I noticed however, was that when I was done the reprograms, the main dash said 'service theft deterrent system' before I took the car out of service mode. Once out of service mode, the main dash did not show any messages. I saw the 'service theft deterrent system' message after each re-programming, because I took it out of service mode and powered up normally in between them.

Has anyone seen this message before? Some quick searches have shown that a degrading 12V battery could cause this, so I'm thinking about replacing that out of caution. I bought the car used and have had it for two years, so it wouldn't surprise me if it's starting to degrade.

Thanks.
 

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One thing I noticed however, was that when I was done the reprograms, the main dash said 'service theft deterrent system' before I took the car out of service mode. Once out of service mode, the main dash did not show any messages. I saw the 'service theft deterrent system' message after each re-programming, because I took it out of service mode and powered up normally in between them.

Has anyone seen this message before? Some quick searches have shown that a degrading 12V battery could cause this, so I'm thinking about replacing that out of caution. I bought the car used and have had it for two years, so it wouldn't surprise me if it's starting to degrade.

Thanks.
I had the Service Theft Deterrent System alert and it was caused by a weak ground connection. You can find details here to compare to your symptoms:

https://gm-volt.com/forum/showthread.php?257233-Service-Theft-Deterrent-System
 

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Thank you quantumorbit for the links and advice, sorry for the late reply.

I tried to find both of the parts from that other thread, the x107 and the g103.

I'm pretty sure I found the x107, it's near the passenger side. If I stand near the front bumper and look at the passenger side of the windshield, and then down, there are two rectangular connection blocks beside each other in a plastic holder part. I assume the x107 must be one of these. I wiggled both, and they did not feel loose. Would I want to disconnect the 12V battery before disconnecting these? I don't expect to find a problem with these, but it would be good to see that they are not corroded on the inside.

For the g103, I don't think I found that one... would I have to disconnect the coolant tank that is front and center? From the technical drawing in the thread you linked, it looks like it would be close to this tank, or maybe underneath. I looked at other bolts to the frame without taking anything off, and didn't see any bad corrosion. There was a little rust, but nothing like the picture showing green corrosion on the connector underneath the bolt head.

Out of caution I will replace the 12V battery soon... It makes sense that a new one would keep electrical problems away.

Thanks.
 

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Hi All,

SHVCS has happened twice again since my last post. The car is currently in that state. I suspect winter temps getting below -10C had something to do with it, but I'm not sure.

The first time, these were the codes that showed:

1 - P0AA6 - Hybrid Battery Voltage System Isolation Fault
2 - P0CD2 - Charge Port Door Unlock Control Performance
3 - P1FFF - DTC P1FFF is an umbrella code

The second time, it had these:

1 - P0AA6 - Hybrid Battery Voltage System Isolation Fault
2 - P1E00 - Request illuminate MIL (check engine light)
3 - P1FFF - DTC P1FFF is an umbrella code

I'm putting together a troubleshooting list, so please advise me however you can. Also, if you could point me to any other threads where I should also post this, that would be great as well.

Troubleshooting list so far:
1 - Read and record the diagnostic measurements for isolation resistance, and other readings about the high voltage system. Can I do this with my 2-year subscription to SPS? I'm assuming it's possible due to the readings I've seen posted. I'll see what options are presented in the UI...

2 - Check for moisture in the trunk and battery pack. I saw this video about a gasoline-electric hybrid SUV getting moisture in the battery pack: https://www.youtube.com/watch?v=lH-CjdWMmWQ

I charge outside, with the charger in my trunk, very often. I may have to stop doing this if I can see water damage. I've heard mention of a drain plug on the battery which can be removed and put back in, and if I stick a rolled up paper towel in here, I could check for moisture or coolant. Has anyone located this drain plug? I can only see plates and shields on the bottom of the car.

If I see moisture like this, I'd have to try to stop it getting into the pack... which may be hard, but I'd still know the heart of the problem.

3 - Calibrations. Is there a calibration setting that I can manipulate when the ECMs are programmed? If I find that they are not set to the newest, I would reprogram the HPCM2 and BECM with the newest and then see how long it takes for the SHVCS message to come back.

4 - Upgrading the firmware on other modules. quantumorbit stated earlier that he updated a list of modules: Battery Charger Control Module, Body Control Module, Coolant Heater Control Module, Engine Control Module and Electric Power Steering Control Module.

I only reprogrammed the HPCM2 and BECM, so that is one delta between his process and mine. I would upgrade all of these to the latest version, then see how long it takes for the SHVCS message to come back.

5 - Start and stop the car with the coolant sensor in different positions to see if that wiring is provoking this. I don't expect this to have any effect, because the P0AA6 code indicates a isolation fault in the 300V battery... not a low coolant level.

6 - Replace the 12V battery. I have not yet replaced this... shame on me. I have seen a 'service theft deterrent system' after reprogramming the 2nd last time, but not on the last time. The only thing though - the vehicle can turn the engine over fine, I don't hear any noise like an ICE car starting when it's very cold. If nothing else seems to help though, this is worth a try despite the cost.

If the above steps yield no useful information, I guess I'd have to assume it's a problem with the wiring or the 300V battery. At that point I'd have to ask, does anyone know who is the best dealership in Ontario for Volts? I'm out of warantee b/c I'm over 160,000km in Canada. It's worth a drive if they are quite knowledgeable and I wouldn't be just throwing money away dealing with them.

Any advice about this approach would be awesome. Thanks again everyone.
 

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I'm checkin the Service Manual for 2012 Volt, HPCM X1 connector, PIN 32 is labeled AC Refrigerant High Temperature Sensor Signal, circuit 732, Color: WH/L-BU and PIN 33 is labeled Low Reference, circuit 452, Color: BK/VT. According to diagram you shared, PIN 32 is circuit 68, Color: L-BU/YE and PIN 33 is circuit 476, Color: BK/L-GN. It might be possible it corresponds to a different year model or Ampera has a different schematics. Nevertheless, I'll try to verify correct PINs during the weekend.

Again thanks for your help.
kwantorbit. Did you find these pins on HPCM2?
 

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My early 2012 developed the Service High Voltage Charging System error message months after having installed the WOT sensor replacement.
This thread originally began with the OP wondering about failures where SHVCS was triggered even with WoT's plug. Well, that just happened to me. I had the SHVCS four times before moving to WoT's plug. It's been solid for some time, but SHVCS triggered today. BUT, what makes this curious....is that when I checked under the hood....my batter coolant bottle was TOTALLY empty! Well, that's not good. And is very interesting. Now, everyone will be saying that Wot's plug is fine and SHVCS triggered because other sensors detected the low coolant. But, no. Long time veterans on this topic will know that WoT in multiple posts was absolutely clear that the ONLY way to trigger SHVCS was THIS sensor. But, this sensor on my Volt is currently just WoT's plug. So....WoT's plug has unfortunately failed for me and it's coincidence the fluid actually IS empty. Who knows how long it's been like that. As WoT stated, and actually tested himself, Volts can operated with an empty battery collant bottle.
So, add my experience as a data point that WoT's plug (actually WoT's 2nd son's plug, lol) can fail. I'll mention I was an early tester of his plug before he started sales, so his 'production' plugs may have been refined - maybe?
 

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And write us what DCT you have revealed? WOT wrote about the fact that there can be many other errors. It is true that he also wrote that SHVCS is revealed only as a result of low level or problem with the installation. So the question is what is the module saying now? I have two errors P1FFF and P1E00 with a 2.47km resistor connected. That is, I removed a magnetic contact from the sensor that contained a value of 17.4 to zero. And the error occurred again. The fact that after 7 days but occurred. I was surprised by the frozen frame that showed the 0.00kochm insulation test. This is a short circuit. After connecting GDS2 and doing the test I have the result = 650kochm, so the question is where is hypocrisy ?. Someone describe how to check the insulation with a meter. Maybe it is a problem with some 380V device. The only question is why the errors concern the sensor and there are no others?
 

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And write us what DCT you have revealed? WOT wrote about the fact that there can be many other errors. It is true that he also wrote that SHVCS is revealed only as a result of low level or problem with the installation. So the question is what is the module saying now? I have two errors P1FFF and P1E00 with a 2.47km resistor connected. That is, I removed a magnetic contact from the sensor that contained a value of 17.4 to zero. And the error occurred again. The fact that after 7 days but occurred. I was surprised by the frozen frame that showed the 0.00kochm insulation test. This is a short circuit. After connecting GDS2 and doing the test I have the result = 650kochm, so the question is where is hypocrisy ?. Someone describe how to check the insulation with a meter. Maybe it is a problem with some 380V device. The only question is why the errors concern the sensor and there are no others?
did you solve your problem, I have the same problem right now
 

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