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Discussion Starter #1
Kudos to WOT for developing his battery coolant level reservoir sensor replacement/defeat plug. This device essentially mimics the electrical characteristics of a properly functioning OEM coolant reservoir sensor. The stock/OEM sensor is a cheap and flakydevice that can and does fail, causing the setting of fault codes that require dealer level tools to clear the codes.

My early 2012 developed the Service High Voltage Charging System error message months after having installed the WOT sensor replacement. This occurred after a successful recharge while still connected. I scanned for the DTC fault codes with a tablet running the Torque app. Initially the codes were B2AAA, P0AA6, P003E, P1FFF, P1FFF. I tried to clear the codes with the Torque app but as WOT has previously posted only dealer level tools can clear all these codes. The clearing process is in fact a reflashing of the software for the HPCM2 module. After my attempt at code clearing another scan reported P0AA6, P1E00, P1FFF.

I could not charge the battery with either my L2 charger or the stock L1. I uninstalled the WOT defeat plug and reinstalled the original stock sensor prior to bringing the Volt to my original new selling dealer service department. All recalls and servicing have been performed by this dealership. The dealer's diagnosis/repair efforts stopped at square one when they discovered that their Fluke 1587 multimeter was missing and was a required tool in the GM diagnostic procedure. Surprising to me was that the next closest Chevrolet Volt dealer also did not have the required instrument. I guess this is a reflection of how few Volts they service. I had to travel to a dealer a hour away who had the required tool.

I was thinking that there must be some real failure, separate from the reservoir coolant sensor issue, that was casing the faults. Possibly a harness issue as a result of poor workmanship when the battery compartment structural enhancement recall was done a couple of years ago. I had asked the dealer service writer to have the tech perform a reflash of the HPCM2 and Battery Energy Control Module to clear the latching error codes as a first step to see if the faults would then reappear. They refused saying that they needed to follow the documented GM diagnostic protocol steps.

They called a day later to report the Volt was now repaired with nothing other than module reprogramming. The notes on the invoice are:
"Scanned for P0AA6 and P1FFF. Isolation test resistance 250K. Bulletin PIC59206 requires to check coolant level, check moisture in battery as well inspect plugs. No issues found. 2880268 reprogram HPCM2 and BECM"
"The HPCM2 is up to date but not BECM. Programmed BECM and tested resistance. Now at correct specs 3000K. All OK at this time. Programmed CD0D3."

I am glad the Service High Voltage Charging System error message is now gone and I will be able to recharge the battery. But, all of the above is a bit baffling to me. With the WOT coolant sensor defeat plug in place for months without issue and the coolant level at the revised proper level, what triggered the error codes? How could reflashing/reprograming the HPCM2 and BECM cause the isolation resistance measured with the Fluke 1587 multimeter to change form an apparently to low 250K to a proper 3000K? This sound illogical to me. And what is the CD0D3 that was reprogrammed, and what does it have to do with the fault? I cannot find anything about the CD0D3.

Should I know reinstall the WOT sensor coolant defeat plug or leave the apparently correctly functioning coolant reservoir sensor in place?

WOT, if you see this post I would appreciate your take on this and guidance.
 

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I am extremely curious if you were billed or not. Was this covered under warranty, and if so what warranty code was used if any. Thanks, as I have a friend that just got the service high voltage message in a 2013.
 

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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.
 

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Discussion Starter #4
I was not charged for the reflash/reprogramming work. I don't see anything on the invoice other than N/C. which I think means no charge. I do have the GMPP extended warranty in place but it is just about to expire. I don't see that they charged this work to the extended warranty although the dealer is well aware that I have the coverage. I am wrestling with the wisdom or folly of purchasing a new extended warranty. I don't think I have ever used the GMPP warranty and because I have the Basic plan I am not sure if it really would cover the Volt specific components after the 8 year Voltec warranty runs out. Also, GMPP is no more, now offered by Ally under a different name, so effectively 3rd party insurance. I am not sure if the new GMEPP extended warranty would cover Volt specific components. I am worried how costly it will be to troubleshoot and repair Voltec components after that warranty expires. What to do?
 

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Discussion Starter #5
Regarding mpmoore79 post, I think that WOT, who developed the coolant sensor defeat plug, says that the problem with repeated faults lies with the sensor itself, which is a device used for windshield washer fluid reservoir. Since you are a Volt tech, do you know what a CD0D3 is? The dealer tech noted that he reprogrammed it but I have no idea what role it plays.
 

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Although I have no Chevy Volt, the issue with low currents and contact resistance did affect my 1995 Buick Regal once, impacting the electronic ignition system and preventing the car from starting. After I was told the cause by the service department tech (I keep excellent relationships with them always for every GM car), I kept the contacts clean and protected by using Radio Shack's Contact Cleaner and Lubricant, which is based on a very thin mineral oil. After twenty one years of ownership, the problem never returned. I sold the Regal in December 2015 and the new owner is enjoying it.

It is rare that this happened but I try to prevent this problem in my present cars (my 2009 Chevy Equinox) by inspecting all the known cables and connectors in the engine bay. Up to now, none have problems, and all seem well attached.
 

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The CD0D3 is a warranty code that the lap top computer gives out after the program is complete so GM can track what module was programmed. This is a internal code that is required by GM so the dealership can get paid, its not a code that was set in the car.

If it was my car having the issue and I was to install the defeat sensor, I would wire it next to the HPCM2. You would have to splice in to the harness but its not that hard. The HPCM2 is just in front of the front passengers seat under the carpet, there is a cut out in the carpet to get to the HPCM2 so you do not need to remove the carpet to get to the module.
 

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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.
I'm jealous of you folks in Phoenix who would be able to get this Volt tech to perform work on your car!:D


So if there is just a small amount of resistance in the circuit, it can cause this issue.
I believe saying more resistance than normal is a better description but I get your meaning and I think we are lucky to be able to share your knowledge on these forums. Thanks!:)
 

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I'll believe mpmoore1979's fix works (kudos!). A question remains though is first, why it's necessary, and second, why it works.

My hypothesis: grounding and ground loops.

For about 100 years so far, manufacturers of cars (and airplanes) have cheaped-out by using the vehicle frame to cut the expense, weight, and complication of wiring electrical systems by nearly half. Assuming a negative ground system, a single positive wire supplies a current path from the battery to the device and the path back to the negative battery post is mostly through the body/frame. In ancient times BE (before electronics), this worked fine. In more recent times BD (before digital), less so. Today, AD (after digital), it's a mess.

Why? My old BD airplane is a good example. The ground/frame was a birdcage of welded steel tubing. Sitting on the instrument panel was a good ol magnetic compass. When you turned on the master switch, the compass would swing. Why? Current flowing through the frame would create a small magnetic field around each tube which affected the compass. Okay, that can be adjusted out, right? Sortof. But with each additional load, such as a radio, switched on, the current flow changed which in turn changed the compass reading. The point? With a negative ground system, one has a return path to the battery, but has no clue in how it accomplishes that task, other than it will, like a lightning bolt, take the path of least resistance including paths that may go through other-than-intended devices.

Experiment: With the car running, use a DVM to measure the voltage directly across the battery terminals, say 14.2V. Then start measuring across red & black wires and red-to-ground at other locations. Don't be surprised to get readings other than 14.2V. In the majority of cases, it's because the load in that circuit is pulling the voltage down. Now get long extensions for your DVM leads. Connect one to the (-) battery terminal. Put the other at locations around the car where there are grounding points to the frame. Good chance you will find some showing a voltage reading between that point and the battery terminal when they should be the same. The term for this is ground loop.

The unit Volts is always a reference between two points. Volts (the car) have batteries in the back and most of the electronics in the front. Since there are not individual ground wires for each device, and many of the devices are "grounded" at different places, the situation is ripe for ground loops, with currents flowing between places that should have been at the same voltage potential (namely 0).

BE, a volt and half an amp is unlikely to matter. BD, more so. AD and millivolts and milliamps going where they shouldn't can take the car down.

Compounding issues is that GM and others seem to have forgotten how to do basic electricity. The Volt's ground connections are crappy. The body is thoroughly painted before ground connections are made and they depend mostly on little star washers to cut through the paint to metal. My car had a host of increasingly weird problems until I pulled apart every ground connection (disconnect the battery ground while doing this) I could find, sanded off some paint and reconnected with a little dab of dielectric grease to protect against moisture and rust. Ever since = perfect.
 

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If it was my car having the issue and I was to install the defeat sensor, I would wire it next to the HPCM2. You would have to splice in to the harness but its not that hard. The HPCM2 is just in front of the front passengers seat under the carpet, there is a cut out in the carpet to get to the HPCM2 so you do not need to remove the carpet to get to the module.
@mpmoore1979 I live in Honduras and have zero dealer support here. My Volt has the "Service High Voltage Charging System" with WOTs defeat plug installed. I already flashed the HPCM2 once with the aid of a VCX Nano, was able to delete the latched codes and charge the car, following these instructions: http://gm-volt.com/forum/showthread.php?13194-quot-Service-High-Voltage-Charging-System-quot-Message&p=4153377#post4153377

Nevertheless, the "Service High Voltage Charging System" DTCs are back. I would like to try installing the defeat sensor next to the NPCM2 to rule out harness issues, but I'm having trouble identifying the correct PINs. I have the Service Manual and believe is PIN 25 of K114B Connector 2X1 (Rechargeable Energy Storage System Coolant HVAC Mode Sensor Signal). This is the only descriptions that seems to match this sensor, but it could be that my manual was printed before the Coolant level sensor recall was issued and it simply doesn't include reference to the PIN where this sensor goes to.

I will be very grateful if you can assist me in identifying the correct PINs to install the defeat plug. I haven't been able to enjoy my car for 6 months now.

Thanks
 

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@mpmoore1979 I live in Honduras and have zero dealer support here. My Volt has the "Service High Voltage Charging System" with WOTs defeat plug installed. I already flashed the HPCM2 once with the aid of a VCX Nano, was able to delete the latched codes and charge the car, following these instructions: http://gm-volt.com/forum/showthread.php?13194-quot-Service-High-Voltage-Charging-System-quot-Message&p=4153377#post4153377

Nevertheless, the "Service High Voltage Charging System" DTCs are back. I would like to try installing the defeat sensor next to the NPCM2 to rule out harness issues, but I'm having trouble identifying the correct PINs. I have the Service Manual and believe is PIN 25 of K114B Connector 2X1 (Rechargeable Energy Storage System Coolant HVAC Mode Sensor Signal). This is the only descriptions that seems to match this sensor, but it could be that my manual was printed before the Coolant level sensor recall was issued and it simply doesn't include reference to the PIN where this sensor goes to.

I will be very grateful if you can assist me in identifying the correct PINs to install the defeat plug. I haven't been able to enjoy my car for 6 months now.

Thanks
Are the codes consistent with "low coolant level" alerts? Or are they for some other problem. MANY different things can set "Service High Voltage Charging System".
 

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Are the codes consistent with "low coolant level" alerts? Or are they for some other problem. MANY different things can set "Service High Voltage Charging System".
Actually, only the battery coolant being low, the coolant level sensor failing, or a wiring issue to the sensor can cause that message to appear. That message was created to entice someone to bring the car to the dealer to verify that there isn't an issue with the battery coolant. It has nothing to do with an actual issue with the charging system.

It was created after that early test where a post-crash-test Volt was left sitting upside down for two weeks and caught on fire from leaking coolant. GM went overboard because the Volt was new and we ended up with a message & procedure designed by lawyers. They also made the resulting codes almost impossible for a normal person to clear, again to force a dealer visit.
 

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Codes are: P0AA6, P1FFF and P1E00. In my case the coolant hasn't dropped, I have WOTs defeat plug, so I decided not to perform all the diagnostics in Service Bulletin # PI0961C and assumed the most obvious, a problem with the harness.

Anyways, I would like to install the bypass next to the HPCM2 (K114B) to avoid the extra variables of the harness. Anyone knows the PINs?

Thanks
 

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They called a day later to report the Volt was now repaired with nothing other than module reprogramming. The notes on the invoice are:
"Scanned for P0AA6 and P1FFF. Isolation test resistance 250K. Bulletin PIC59206 requires to check coolant level, check moisture in battery as well inspect plugs. No issues found. 2880268 reprogram HPCM2 and BECM"
"The HPCM2 is up to date but not BECM. Programmed BECM and tested resistance. Now at correct specs 3000K. All OK at this time. Programmed CD0D3."

I am glad the Service High Voltage Charging System error message is now gone and I will be able to recharge the battery. But, all of the above is a bit baffling to me. With the WOT coolant sensor defeat plug in place for months without issue and the coolant level at the revised proper level, what triggered the error codes? How could reflashing/reprograming the HPCM2 and BECM cause the isolation resistance measured with the Fluke 1587 multimeter to change form an apparently to low 250K to a proper 3000K? This sound illogical to me.
The isolation test resistance using GDS2 diagnostics shows 225 kOhm. Could it be that my problem is also BECM not up to date?
HPCM2 Data Screenshot:

HPCM2.jpg

I would still like to install the defeat plug next to the HPCM2 to avoid harness issues, but I can't seem to find schematics to show PINs in the connector to hook up to. Tomorrow I'll try to follow the lines from the coolant sensor to the HPCM2 and figure this out on my own since I've been waiting for weeks here for some feedback with no luck.

This is the Battery Charger Module Data:

Screen Shot 2017-12-16 at 5.45.03 PM.jpg
 

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Fixed by hosting image elsewhere.

Do you know if the "Isolation Test Resistance" shown in my report is equivalent to your "Hybrid/EV Battery Pack Resistance"?
 

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Fixed by hosting image elsewhere.

Do you know if the "Isolation Test Resistance" shown in my report is equivalent to your "Hybrid/EV Battery Pack Resistance"?
1. Vehicle OFF, disable the high voltage at the A4 hybrid/EV battery pack. Refer to High Voltage Disabling.
2. Connect the 12 V battery.
3. Vehicle in Service Mode, verify that DTC P0A7E, P0AA1, P0AD9, P0ADD, P0AE2, P0AE4, P0C32, P0D0A, P0D11, P1EBC-P1EBF, P1EC0 or P1EC3-P1EC5 is not set.
If any DTC is set, refer to Diagnostic Trouble Code (DTC) List - Vehicle.
4. Vehicle OFF, disconnect the 12 V battery
Note: The following continuity tests must be performed using an Insulation Multimeter. Select the Isolation test setting, then select the 500 V range.
5. With the Insulation Multimeter, set on the Isolation test setting, test for greater than 400k Ω between the A28 hybrid battery contactor assembly harness connector terminals listed below and chassis earth:
• Battery charger negative harness side terminal B X5
• Battery charger positive harness side terminal A X5
If less than the specified range, disconnect the X4 connector at the T18 battery charger. Test for greater than 400kΩ between the circuit terminals and chassis earth.
If the test result is greater than the specified value, replace the T18 battery charger. If the test result is less than the specified range, replace the 300 V DC cables and test or replace the charger fuse.
6. Remove the fuse cover and battery protector (Insulator). Refer to Battery Charger and 14 V Power Module Maxi 20 A Fuse Replacement.
7. With the Insulation Multimeter, set on Ohm setting, test for less than 1 Ω across the battery charger fuse.
If greater than the specified range, replace the battery charger fuse.
8. If all the circuit tests normal, replace the A4 hybrid/EV battery pack.


The isolation test resistance using GDS2 diagnostics shows 225 kOhm. Could it be that my problem is also BECM not up to date?
HPCM2 Data Screenshot:

View attachment 144657
FWIW: Not sure If worthy of a software flash to resolve but your Isolation Test Resistance HPCM2 value is reading substantially different on my Gen1 pictured below. This would explain why your Volt has failed the Hybrid/EV Battery Pack Isolation Test Status also.


https://i.imgur.com/Iuqehct.jpg

A single high-voltage contactor stuck closed can set this DTC.
• An open charger fuse may cause a P1AE6 or P1F0E.
• Condensation or water intrusion into the hybrid/EV battery pack may cause P0AA6, P1AE6 or P1F0E to set.
• Low or no coolant in the hybrid/EV battery cooling system may cause P0AA6, P1AE6 or P1F0E to set.
 

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I’ve been driving on gas for over 6 months now. Still haven’t fixed this issue. Tried to follow the cables from the sensor but they merge with a bunch of cables making it a daunting job.
Haven’t had time for other options like looking at cable color codes or checking continuity. Also checked the shop repair manual with no luck.
Will post PIN info whenever I get it done since it seems nobody has done it before or shared it.
 
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