Often this is a source issue more than a draw issue (IE. computer). But disconnect each of those sensors one at a time and check for a voltage drop. I don't have the schematic, but is the too high-11.9v coming from diagnosis or the scanner? is it a good scanner? Often that code can mean one of the 3 sensors doesn't have a signal, and only a sensor needs replaced. You can check each of them for an open circuit.

If you have a drain on the battery, it might not be related to that circuit, unless another system has shorted into that harness and is providing the 12v source. Im not sure where to tell you to check this, either in the ECU, or fusebox perhaps?

If your car is a manual, low optioned car, I have a spare ECU I could send you to try. But any potential ECU coding issues would need sent to dealership anyhow.