@Stegy Frany
Suzuki TSB (Technical Service Bulletin) #TS 04 11307 Which Pertains Only To 2007 SX4 Models Is Interesting.
The bulletin, 1 page with photo, written for Suzuki Technicians, points out that not taking precautions during oil changes, particularly oil filter removal, can contaminate the downstream oxygen sensor internally and possibly set a DTC P0137 AND/OR (Suzuki’s words, not mine) a DTC P0420 Catalyst System Efficiency Below Threshold (Bank-1). Oops.
Suzuki moved the problematic O2 sensor location for the 2008 model-year SX4.
I’m not saying this is the problem, but it is interesting and something to consider. I would think a trashed sensor would not cause an intermittent P0420, but I know better than to dismiss anything automotive at the first chance. I’ve seen some strange stuff apply to vehicles, or any machines, for that matter.
CSA