OBD2 code reader plugged into port under dash, disconnect batt for a while. Note-clearing codes without repair will result in fault reoccuring so light will continue to come back on
Trouble code P0421 means: Catalyst Efficiency Below Normal (Bank 1)
The 2002 Mazda MX-5-Miata has an inline 4 engine.
The 2009 Mazda MX-5-Miata has an inline 4 engine.
The 2004 Mazda MX-5-Miata has an inline 4 engine.
The 2003 Mazda MX-5-Miata has an inline 4 engine.
The 2007 Mazda MX-5-Miata has an inline 4 engine.
The 2013 Mazda MX-5-Miata has an inline 4 engine.
The 2014 Mazda MX-5-Miata has an inline 4 engine.
The 2008 Mazda MX-5-Miata has an inline 4 engine.
The 2001 Mazda MX-5-Miata has an inline 4 engine.
The 2011 Mazda MX-5-Miata has an inline 4 engine.
The 2012 Mazda MX-5-Miata has an inline 4 engine.