P0700 Dodge - magnum

Question

P0700 and p0420 is this caused by a bad catalytic converter? Dealership wants to replace it but friend says its O2 sensor

Answer 1

P0420 Catalytic effieciency 1/1 efficiency

This can be from a 02 sensor. especially if the replace a aging rear 02 sensor you will code P0420. In order for a catalytic convertor to work the it has to go from lean condition to rich condition. What does this is the front 02 sensor. An engine that is in fuel control with a healthy front 02 sensor will result in a functioning catalytic convertor. If the upstream (front 02) 02 sensor is aging it will go lean as a result a P0420 will result. So it is always a good idea to diagnose the front 02 sensor before replacing the catalytic convertor. What is also listed is P0700 this is a transmission request mil light on. it should be accompanied by another transmission code. The purpose of the CK ENG LT is to protect the catalytic, and the catalytic to protect the enviroment.With a transmission code present this can also affect  the function of the catalytic convertor and cause P0420