Location of O2 sensor

If you can locate the catalytic converter the front O2 sensor , referred to as sensor 1 or S1 , is located in the inlet pipe for the catalytic converter , 6" to 12" upstream. The rear sensor , referred to as sensor 2 or S2 , is located in the outlet pipe , 6" to 12" downstream. The exact distance from the catalytic converter varies by engine type , i.e , 2.O liter ,1.8 Turbo or 2.8 VR-6