Ok Now i had all my codes fixed the P0135 ( I believe it was due to Non-Factory O2 sensor Factory one solved issue) Now I recieved the P0138 code and was curious since this is supposedly the same O2 sensor that gives out the P0420 ( Catalyst Effeciency Error Code) Does this Sensor in any way effect the Air/Fuel Ratio or the ability for the Computer to run in the Mode where it uses the other sensors to achieve maximun effeciency?
I know there is a O2 sensor that is Upstream of teh Cat and this Sensor so I was hoping all this one did was analyze the Ozygen difference between teh 2 O2 sensors and Prompt for MIL when Cat is not absorbing O2 or has fallen into the not-effecient reading.
I do remember reading when the Upstrean O2 Sensor was Faulty the Vehicle basically stayed in (Closed Loop I think it was closed) Where the vehicle ran off a preset installed Parameters and did not use the O2, or any other sensor to optimize effeciency

 

there is not a single sensor for the 420 its a math equation that will determine if the cat is working good enough.

 

right the mathe between the Upstream Sensor and teh Downstream sensor ( basically the difference due to less oxygen downstream if CAT is absorbing it properly, I just want to make sure that this is not causing the engine to run Rich or in a preset mode due to the 138 and 420 codes, I can probably bet that my lack of decent fuel mileage is what sent the CAT to early recycler, I guess I know why the van was Traded in and I got a decent price on it even though no Issues at all for about 2 1/2 months after we bought it. First Vehicle I have ever bought where I didn't pay cash for the entire thing although I did Drop 70% I could of gotten a BAD Durango and had some cash left over I knew I screwed the pooch when about a week afterwards I was having a feeling of DREAD without any reasons at that time.

 

drop new converter in it first