2001 Nissan Sentra Q&A

2001 Nissan Sentra Question: how can you tell if the rear catalytic converter needs replacing?

mechanic used computer to scan check engine light problem - said I needed rear catalytic con, which cost me $400 for part and isntallation. Truth is, I needed a new engine as I had cracked head or blown head gasket - due to bad gas. I did not need rear cat con, why did code read that way? -
Answer 1
Your defective head gasket poured out way too much pollution and over worked the CAT. This is common. You most likely had a P0420 code. Check out this article I wrote about this code, it may help shed some light. http://repairpal.com/OBD-II-Code-P0420 -