DTC P0420 - Bank No. 1 Catalytic Converter Efficiency Below Limit: Condition
WARNING: This page is about a different car, the 1997 Mazda Millenia. However, it is still accessible from the selected car via links, so may be relevant.
DTC is set when right front oxygen sensor value difference becomes closer to value of right rear oxygen sensor. Possible causes are:
- 3-way catalytic converter deterioration.
- Exhaust system operation.