I want to replace o2 sensor. What are the 2 sensors in the exhaust and which one is the o2. One is in the exhaust manifold on the passenger side and one is in the DP itself. Im thinking the one in the DP is the O2 sensor but whats the other one for and should i replace that one too? I have a 94wrx with stock DP at the moment. The reason for replacing the o2 is that recently my car seems to be shuddering at WOT at around 4-5k rpm and I failed emissions tests.

Thanks,
Garrett

 

on your car its on the manifold, one on the down pipe is a cat on fire sensor