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Q:

cel with p0421 and 431...how can i troubleshoot and determine the root cause on 2003 Audi A4 Quattro

Rookie cbe0621eac06868b3efe0d8d1d3611e23c60d3114864ea2ec19a68cfbd3eebab
Car passed emmision test last week...Would like to determine the root cause before repairing...don't want to just replace the cats and the o2 sensors...Where can i get an accurate diagnosis?
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