a) there are three groups of codes, KOEO, KOER and CM. You
MUST repair them in that specific sequence, AND withing each code group you
MUST start with the lowest number code first and work in ascending numeric order. Diagnose the reason for the code, clear codes (will be clearing all of them), drive, test for codes to verify code free condition. Repeat this sequence until code free operation is achieved.
If your information is correct, then 157 is the first one to tackle Besides, seeing the O2 codes in there is a reinforcing hint.
b) Generally speaking, following the diagnostic flow charts in the FSM is the simplest and most effective way to diagnose the cause for a code.