briel

Hi, this is a great forum. Happy to have found you all. I searched and read a number of topics here, but couldn't find an answer to an odd question. I own a 2009 Impreza 2.5i sedan. I'm seeing only a 0420 code that appeared at about 65,000 miles. I monitored this with my OBD II meter while driving, after resetting the car's computer. I found that the 0420 appears immediately when the o2 HEGO monitor completes, but the cat efficiency monitor is still incomplete. Could this indicate that the issue is an o2 sensor, rather than a bad cat? Wouldn't the Cat efficiency monitor need to complete in order for the 0420 to indicate a bad cat converter (or just in general that the efficiency of the converter has even been tested?). Also, the engine seems to have a loss of power lately, and I read that a bad upstream o2 sensor could cause this behavior (amongst several other things.) I also read that it's not uncommon for the o2 sensors to fail after 50k. I'm inclined to replace both o2 sensors, but wondered if anyone had experience with seeing the 0420 after HEGO monitor completes but before the Cat efficiency monitor is complete. Thanks.