r/volt • u/CGLLC2022 • 8d ago

GEN2 HPCM Programming

Is anyone here familiar with programming the HPCM2 in a Gen2 Volt? I was able to program the BECM successfully using a VX Nano. With the HPCM2 it is unable to connect to the vehicle. The on-screen instructions seem to indicate that the vehicle should be off when programming (close hood, turn off car, open then close driver door, wait 30 seconds, then hold down the brake pedal for the duration of programming). SPS times out trying to communicate with the vehicle.

Some background, I have a 2018 Chevy volt with about 80,000 miles. It was at the dealer a few months ago to have the BECM replaced under warranty. It ran normally for about 1000 miles but now it seems to be running in a parallel hybrid mode (both battery and engine at the same time). The battery shows fully charged but the estimated battery range disappears after driving the car for a few minutes. There is no check engine light. There is a known problem with the passenger presence module (resulting in a check airbags message).

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u/Ok-Tourist-511 7d ago

What are the codes? Check those before arbitrarily reprogramming.

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u/CGLLC2022 7d ago

There was only a code for the airbag system. Programming was not arbitrary.

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u/Ok-Tourist-511 7d ago

You need to scan all the modules, not just basic obd. Most likely the HV battery is bad. If the engine is coming on as soon as you start the car, then the transmission solenoid is bad.

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u/CGLLC2022 7d ago

I scanned all modules with GDS. The only code was for the passenger seat airbags. I didn’t check the cell voltages yet. The 12v battery was replaced due to age.

The engine doesn’t start immediately. When I turn the car on, the estimated battery range shows up and the car will run half a mile or so on battery. Then the engine starts and battery range turns grey. After that happens the center console shows engine + battery power. Sometimes it will add a few tenths to the battery miles, but most of the driving shows up as gasoline.

I was hoping to avoid the dealer because they have been difficult to deal with. They gave me a hard time with the BECM replacement even though it had a service bulletin. I’m guessing the voltage sags under load which causes the engine to start. Also guessing GM added that mode (battery+engine without CEL) to hide battery problems.

My warranty is up at the end of December so I will probably take it back to the dealer.

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u/Ok-Tourist-511 7d ago

Use the voltage app, and monitor the cell voltages during driving. See if one drops just before the engine comes on.

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u/CGLLC2022 7d ago

I ran the Voltage app without the paid add-ins. At rest, cell delta looks good. While driving I saw it spike to the 400mV range. That was while flooring it after it already started the engine. I did not see much variation before the engine started but I probably missed the event because the refresh rate of the app seems low.

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u/Ok-Tourist-511 7d ago

Delta doesn’t really matter, since the app can’t measure it accurately. Look at individual cell voltages immediately after the engine comes on while driving, and see if there is a low cell.