What is wrong to get codes P0171 & P0420 on 2003 Toyota Corolla & How much should it cost to repair?

Question

What would cause codes p0171 & p0420 in a 2003 Toyota Corolla

Answer 1

Hi there,

The P0171 is for a lean fuel mixture and the P0420 is for the converter working below threshold. What I see most of the time is the converter plug up and cause the lean fuel mixture.