P0121 - Throttle Position Sensor
1 Performance - Probably a bad throttle body, and needs replacement.
B0081 - Passenger Presence System Error - This has to do with the airbag
system for the front passenger seat, it can tell when someone is sitting in the seat or not and turns on/off the airbag accordingly. Normally there is a problem with the module, or wiring connectors under the seat. This can take a bit of diagnosis to determine the cause.
B2645 - Ambient Light Sensor Circuit - This is for the sensor on the dash that detects whether it is day or night. Usually the sensor need replaced.
C0267 - Low Brake Fluid Detected - This is for the sensor in the master cylinder to detect if the brake fluid is low or not. Sometimes you can replace the sensor, or other times you need a new master cylinder assembly.
C0899, C0900 - These are the low voltage codes I explained previously. Either due to a faulty battery or something wrong with the charging system.