P0420 - Catalytic converter system, Bank 1, efficiency too low (Solution)

Error code P0420 - Catalytic system Bank 1, insufficient efficiency means that one or more of the following conditions apply:
- Fault Lambda sensor and/or catalytic converter due to fueling with unsuitable fuel.
- Wiring for lambda sensor is faulty.
- Coolant temperature sensor is providing incorrect values.
- Damaged/leaking exhaust system.
- Incorrect ignition timing (if not controlled by the engine control unit).
- Misfires.
- Oil contamination of the exhaust system (catalytic converter and sensors).