OBD codes 0731 and 0876

Hello,

The codes
P0731 Gear Ratio Error in 1st
P0876 Pressure switch Rationality

These can get triggered due to a number of reasons.
It could be due to low fluid level, stuck main regulator valve, failed clutch, having low line pressure, faulty wiring for input sensor, cracked seal for the oil sump. It can also happen due to fault in the PCM.

I have attached the trouble shooting steps for these codes below.
Follow those steps as it can help you determine the issue.

Let me know what you find or if you have any questions.
Thank you.

https://www.2carpros.com/articles/automatic-transmission-problems