Swapped 4 O2 sensors on a 2011 Civic and the code came back in 20 minutes
Last Friday I did all 4 O2 sensors on a 2011 Civic with 163k on the clock, bank 1 and bank 2, and the P0420 showed up again before the customer finished his lunch. I figured the upstreams would fix the fuel trim, so I did those too, another $180 in parts plus my labor, and the freeze frame looked the same as the day it rolled in. Turns out the cat was gutted from a bad coil years back and no sensor on earth was going to change that. What got me was that my scanner showed the downstream switching like a good sensor should, so I chased the wrong part of the circuit for two hours. I pulled the front pipe and looked inside with a cheap borescope, and the honeycomb was a melted mess. Now I look at the cat before I sell a single sensor. How do you guys handle a customer who already paid for the wrong fix?