Three Way Catalytic Converter (TWC): Inspection

If excessive exhaust system back-pressure is suspected, remove the TWC from the car and using a flashlight, 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.

Fig 1: Checking For Plugging, Melting Or Cracking Of Catalyst Using Flashlight

Courtesy of AMERICAN HONDA MOTOR CO., INC.

[P0420] The scan tool indicates Diagnostic Trouble Code (DTC) P0420: Catalyst system efficiency below threshold.