Mitsubishi Repair: 04 Lancer ES, 2.0 auto, threshold bank, oxygen sensor

Question
Check engine light is on. Code is P0421 – Warm Up Catalyst Efficiency Below Threshold (Bank 1). Can you tell me is this is
caused by a low reading from the oxygen sensor or a bad catalytic converter. Any advise is very much appreciated.

Answer
Russ,
I'm not too familiar with this car, but I am aware of a recall that Mitsubishi issued for both the cat converter and the PCM.  I believe it was for 2002-2005 Lancers, so you may want to take your car into the dealership and see if it is part of recall.  Free repairs/replacements are always good.
Good luck!