P0420 SUBARU -

Question

After having had that code a first time, the front O2 sensor has been changed.
shortly after, the same error code made the CEL go off.

no other error code.

SAAB 92x 2006 (same as subaru impreza 6 cyl), 140 000 km

Answer 1

HI there,

Typically the rear O2 sensor would be the cause if the sensor itself is the problem. In most cases though the catalytic converter is the cause of the issue and will need to be replaced.