Q: to pass smog check P0420 catalyst system efficiency below threshold bank 1, what is the total cost of repair

Hi there. Typically the P0420 OBD II trouble code is caused by a faulty catalytic converter, however it can also be due to a worn out front bank O2 sensor, faulty rear O2 sensor or damage to wiring harnesses to sensors. If you smell a rotten egg smell while driving, it’s likely the catalytic converter that will require replacement. Without knowing exactly what is causing the failed smog test, it’s very difficult to give you an estimate on repairs. The best way for us to attempt the repairs is to first complete an onsite check engine light inspection so our mechanic can download all stored error codes (beyond the P0420 code) that could help pinpoint the primary source of this issue.