P0420 Subaru - What should next step be?

Question

I have already replaced the catalytic converter and it did not fix the problem. I have replaced the o2 sensor but the light comes back on after ~4000 miles. Should I just keep replacing the O2 sensor or is there another step I should try? thanks

Answer 1

Hi there,

First, if you didn't use a factory catalytic converter, it could very likely be the problem. The aftermarket don't meet the tight restrictions Subaru builds into the computer.

Also, keep in mind the car has 2 O2 sensors, you don't say which you have changed here, but typically the rear O2 is the one that could still cause the code to come up.

Finally, if the car hasn't had a tune up in a while, it might simply be running to rich and throwing the converter code.