Video linked below shows replacement of pre and post catalytic converter O2 oxygen sensor.
Link:
http://www.youtube.com/watch?v=Y0wjJ6YFPSc" onclick="window.open(this.href);return false;
Had been getting a random P0420 error for the last 2000 miles. It seemed to come on when starting on cold days, but would occasionally come on at other times. Details from the previous owner, they had the post catalytic sensor replaced about 25k miles ago. After the sensor harness was damaged by driving over roadkill. Knowing that the rear sensor was newer and the condition seemed to be related to cold, decided to first replace the pre cat sensor. After about 300 miles this made the code come on nearly every start up. Given the history of the vehicle, the best guessed turned out to be wrong. Replaced the post catalytic sensor, the previous replacement was not OEM, things are now good.
Used the following parts for 2005 1.8L FWD. AWD, 2.4L, and other years might use different versions. Shopped around, NAPA, Autozone, Advanced, Oriely's were all within a few dollars of each other. Of all places, Amazon had the best deal by a long shot, (May 2014) on the sensors and socket.
Pre Catalytic Convertor Denso P/N 234-9052 ($88.26)
Post Catalytic Convertor Denso P/N 234-4233 ($47.30)
Socket set used: Alltrade 948005 Master Sensor Socket Kit - 7 Piece ($24.58) Okay quality, for shade tree mechanic. For both O2 sensors you will use the 7/8" crows foot socket.
Things learned from the P0420 error code:
-Code is vague, only gets you in the vicinity of the problem Check out the following video for tips on diagnosing the problem:
https://www.youtube.com/watch?v=9VZ5K8n5jj0" onclick="window.open(this.href);return false;
-Guessing which 02 sensor is causing the problem is a best guess. Unless you have the proper scan tool.
-Post cat sensor can easily be damaged due to open air wiring that roadkill, debris, and weather can impact.
-Do any engine flushing cleaning before replacing the O2 sensors, prevent damaging the new sensors