i just replaced the #3 coil and after driving for awile i got a po420 code .

Question

What can be the issue with a po420 bank 1 code

Answer 1

Hi there,

If it was misfiring for a long time it could have put a lot of raw fuel into the converter on bank 1. I would clear the code and continue to drive the car. If the code returns, then it's likely the extra un burned fuel in the converter has done damage and the converter will need to be replaced.