Hi,
That's a lot of codes. The one that really matters is the B21C6. It is the only active code present. When that code is present, the hydraulic pump has lost ground. That could explain the voltage codes and the PTCM code. I will also tell you that if the B2278 was "Active" and not stored, the module would need to be replaced.
Since both are present, chances are it is a ground issue, but the PTCM may have failed as well.
I attached diagnostics below. Take a look at them and let me know if you are comfortable performing them. Also, note that the ground location (G303) is on the left rear quarter panel. I attached a pic below. (see the last pic) The arrow in the pic points toward the front of the vehicle. Also, that ground is also for the trunk release.
Here is a link you may find helpful:
https://www.2carpros.com/articles/how-to-check-wiring
Let me know.
Take care,
Joe
See pics below.
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Saturday, August 12th, 2023 AT 9:24 PM