Update: I found this website (Nissan accelerator pedal position (APP) sensor - Erwin Salarda) that breaks down the code and found that, outside the USA, the Altima is also known as the Teana. It shows several different components that a P2138 error could be thrown by but I haven't found any corroborating information about anything listed. Instead, the only other information I've found says that it could be "an issue with the computer" (with no clarification on what I would need to do in that case) or my TPS or throttle body. Since the guy at O'Reilly's didn't really give me a long enough look at the code, I'm not 100% sure that it's P2138 specifically but I do remember it saying Accelerator Pedal Position Sensor something something for all 6 codes. If anyone here has had to diagnose something related to the APP sensor and has some insight as to where else I may need to look if my wiring, connector, battery, and sensor appear to be fine, I would greatly appreciate it. I do DoorDash for work and can't really afford to be without my car for extended periods and don't really want to throw money at it by unnecessarily replacing parts.