I have a 2003 Accord V6. Got an O2 downstream sensor malfunction and replaced it. Now I'm getting a P0420 code - catalyst efficiency below threshold (Bank 1). I was told that the ECM needed to be reflashed to read the new O2 sensor. Is someone pulling my leg?
Thanks

 

The ECM does not need to be reflashed to read the new O2 sensor. P0420 is usually the catalytic converter or an exhaust leak. If the car didn't have this code prior to the oxygen sensor code, then I would first check for an exhaust leak.

Although this is probably not your case, if the Accord was a hybrid; IIRC, there was a Honda technical service bulletin (tsb) regarding updating the ECM software for P0420.