hi have just bought an sti 8 jan 2003 jap import. there are 2 sensors on the cat down pipe from the turbo one is next to the turbo and the other is at the end that fits on to the rest of the exhaust. please can you tell me which one is the oxygen sensor. i am fitting an aftermarket de-cat pipe to which i have to connect the oxygen sensor. many thanks. ps i have already fitted blitz spec r exhaust.

They're both oxygen sensors.

 

The first oxygen sensor sends information to the ECU for a/f ratio control.

 

The second oxygen sensor is a catalytic converter efficiency monitor. The second oxygen sensor is not really necessary to run, but it will throw a check engine light.