CEL P0421 Warm-up catalyst system (RH) efficiency below threshold ON 2 Catalyst

[zigger]

Hey guys...I got this code tonight for the very 1st time ever..P0421 Warm-up catalyst system (RH) efficiency below threshold ON 2 Catalyst

I cleared it with my dash hawk..anyone else get this? Is this a seriouse cel ?
Thanks

[Rutedown]

Do you have a hi-flow catalytic converter or are you running without one? Your O2 sensor is getting a reading that is either to high or low where it's triggering the light. It's not serious if what I mentioned is true. If you have a stock exhaust then you could have a bad cat.