I've had the cat efficiency code for some time now which I didn't really bother.
I put the stock cat back on and the light is still there.
Reset the ecu, and it was gone. Next day, it came back on again.
O2 sensor?
should I check to make sure its the cat code? (0420 i believe).
which O2 sensor if I need one?
mitsu stealers want $400 for oem o2 sensor