Catalytic Converter Inspection

If excessive exhaust system back-pressure is suspected, remove the TWC from the vehicle.
Using a flashlight (A) and plug (B) (KU, KU-H, FO, MA, PH models) make a visual check for plugging, melting or cracking of the catalyst.
Replace the TWC if any of the visible area is damaged or plugged.

KU, KU (RV-i-H, RV-Si-H models), FO, MA, PH models: 

KN, KM models: