4.2L CDRA

Right Side 

1. 3  - Oxygen sensor after three way catalytic converter -G130-
2. 4  - Heated oxygen sensor -G39-

Courtesy of AUDI OF AMERICA, LLC

Left Side 

1. Heated oxygen sensor 2 -G108-
2. Oxygen sensor 2 after catalytic converter -G131-

Courtesy of AUDI OF AMERICA, LLC