Q: P0421 comes up on scan. What is the likely culprit

Hello. When you get the P0421 code, it usually means that you have a failing catalytic converter. It is very common for converters to fail on this vehicle over time. Most of the time I use a scan tool to check the output of the oxygen sensors first, as a bad sensor can cause this code. If the sensors are reading right, then the converter will need to be replaced. If you want to have the code diagnosed, a certified technician from YourMechanic can come to your car’s location to pinpoint the proper repair.