P0491 16875 Secondary Air Injection System Insufficient Flow Bank 1
P0492 16876 Secondary Air Injection System Insufficient Flow Bank 2
Would indicate possible problems with Secondary Air Injection (AIR) pump relay -J299-
and/or
Secondary Air Injection (AIR) solenoid valve -N112-
and/or
Secondary Air system seal
PM me your email address and can send you a pdf on testing these aspects.