Code P0641, could it be a bad alternator?

Do you have any other codes? If the engine runs let's check the alternator output, this guide can help:

https://www.2carpros.com/articles/how-to-check-a-car-alternator

With the system on test the 5-volt references to each sensor and look for the one that is low and replace that sensor. This guide can help, and I have included the engine PCM wiring diagrams so you can see how the system works and which sensor wires to test.

https://www.2carpros.com/articles/how-to-check-wiring

code P0641 "Sensor Reference Voltage 'A' Circuit/Open."

Check out the images (below). Please let us know how it goes.