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2012 Service High Voltage Charging System with WOT's Sensor Defeat Plug in place ????

29830 Views 55 Replies 23 Participants Last post by  Rollmann
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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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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· Registered
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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.

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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