Geo Prizm P0420 Fault: How to Diagnose O2 Sensors, Catalytic Converter or Coolant Temp Sensor

Model: Geo Prizm Fault Code: P0420 Posted: 2005-06-10 20:16

I own a 1996 Geo Prizm and recently the check engine light came on with fault code P0420. I'm looking for reliable testing methods to determine whether the issue is caused by faulty oxygen sensors, a failing catalytic converter, or an incorrect engine coolant temperature sensor. Can anyone recommend specific diagnostic steps or tools to help identify the root cause?