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.